Respiratory syncytial virus (RSV)

What

RSV (respiratory syncytial virus) is a virus that causes upper and lower respiratory tract infection. RSV infection can cause severe disease, particularly in very young and older people.

Who

RSV vaccination is recommended for:

• pregnant women to protect their newborn infant
• all people aged ≥75 years and Aboriginal and Torres Strait Islander people aged ≥60 years
• people with medical risk factors for severe RSV disease aged ≥60 years.

RSV monoclonal antibodies are recommended for:

• young infants whose mothers did not receive RSV vaccine in pregnancy, or who were not vaccinated at least 2 weeks before giving birth
• young infants who are at increased risk of severe RSV disease, regardless of their mother’s vaccination status
• children aged <24 months who have medical risk factors for severe RSV disease in their 2nd or subsequent RSV season.

Non-Indigenous adults aged 60–74 years who do not have a medical risk factor for severe RSV disease may also consider vaccination. There are benefits of vaccination in this age group, but the benefits may be less than for those aged ≥75 years, because of a comparatively lower risk of severe RSV disease.

Adults aged 50–59 years who have a medical risk factor for severe RSV disease may also consider vaccination.

Risk factors for severe RSV disease differ between infants (see Table. Conditions associated with increased risk of severe RSV disease in infants and young children) and adults (see Table. Conditions associated with increased risk of severe RSV disease in adults).

How

A single dose of RSV vaccine is recommended to protect older people. RSV vaccine may be given at any time of the year, but, where possible, should be offered before the start of the RSV season. The 2 RSV vaccines registered for use in adults aged ≥60 years are Abrysvo and Arexvy. There is no brand preference for this age group. The need for further doses has not yet been established.

A single dose of Abrysvo is recommended for use in pregnant women to protect their infants. Administration is recommended in each pregnancy from 28 weeks gestation. Infants are unlikely to be adequately protected if they are born less than 2 weeks after their mother received the vaccine, so administration by the end of 36 weeks gestation is encouraged.¹ 

A single dose of nirsevimab – a long-acting RSV-specific monoclonal antibody – is recommended before their 1st RSV season in certain young infants:

• whose mothers who were not vaccinated at least 2 weeks before giving birth
• where protection from maternal vaccination may be reduced because of maternal or infant conditions
• who have medical risk factors for severe RSV who may need additional protection 

Whilst nirsevimab can be given year-round, the benefits of administration immediately after birth versus just prior to the first RSV season should be considered based on individual risk and jurisdictional RSV seasonality.

Additionally, nirsevimab is recommended from shortly before the start of the RSV season for infants who have medical risk factors for severe RSV entering their second RSV season. A short-acting monoclonal antibody (palivizumab), which is given monthly for 5 months, may be used as an alternative if nirsevimab is not available.

Why

RSV infects most children by 2 years of age. RSV infection is associated with substantial disease burden (in both inpatient and outpatient settings) and is a leading cause of lower respiratory tract disease hospitalisation in infants aged <12 months.^2-6 Most infants hospitalised with RSV disease are otherwise healthy.⁴ However, those with medical risk factors have an increased risk of severe disease.

RSV is also an important cause of respiratory disease and hospitalisation in older people, Aboriginal and Torres Strait Islander adults, and people with conditions that increase their risk of severe RSV disease.

RSV vaccines available in Australia

The RSV vaccines Abrysvo and Arexvy are different formulations and are registered for use in a specific age or population group.

Only Abrysvo is to be used in pregnant women.

Arexvy is indicated for use in adults aged 50-59 years with medical conditions that increase their risk of severe RSV disease and all older adults aged ≥60 years. Arexvy should not be administered to pregnant women.

Neither RSV vaccine should be given to infants or children, and there are no vaccines currently licensed in this age group. The RSV monoclonal antibodies nirsevimab and palivizumab are available to provide passive immunisation in infants and children aged <2 years. They should not be used in children ≥2 years of age or adults.

The Therapeutic Goods Administration website provides product information for each RSV vaccine.

See also Vaccine information and Variations from product information for more details.

RSV-specific monoclonal antibodies available in Australia

Two monoclonal antibodies are currently available in Australia, Beyfortus (nirsevimab) and Synagis (palivizumab).

Nirsevimab is preferred over palivizumab because it is long acting (it requires only a single dose to cover an RSV season) and is registered for use from birth in all infants.

If nirsevimab is not available, palivizumab may be considered in infants with risk conditions for severe RSV disease. See Table. Conditions associated with increased risk of severe RSV disease in infants and young children.

Dose and route

Abrysvo and Arexvy

The dose of Abrysvo and Arexvy is 0.5 mL, given by intramuscular injection.

Nirsevimab

The dose of nirsevimab for infants weighing <5 kg, born during or entering their 1st RSV season, is 50 mg (0.5 mL), given by intramuscular injection.

The dose of nirsevimab for infants weighing ≥5 kg, born during or entering their 1st RSV season, is 100 mg (1 mL), given by intramuscular injection.

The dose of nirsevimab for older children entering their 2nd or subsequent RSV season is 200 mg, given as 2 intramuscular injections (2 × 1 mL of the 100 mg/mL formulation) at 2 different sites (preferably separate limbs, or else separated by 2.5 cm) during the same visit.

For children undergoing cardiopulmonary bypass, an additional dose of nirsevimab should be given as soon as the child is stable after surgery.

If the surgery is ≤90 days after receiving nirsevimab:

• The additional dose of nirsevimab for infants born during or entering their first RSV season is based on body weight at the time of the additional dose (see above).
• The additional dose of nirsevimab for older children entering their 2nd or subsequent RSV season is 200 mg (see above).

If the surgery is >90 days after receiving nirsevimab:

• The additional dose of nirsevimab for infants born during or entering their first RSV season is 50mg, regardless of body weight.
• The additional dose of nirsevimab for infants born during or entering their 2nd or subsequent RSV season is 100mg, regardless of body weight.

For children aged ≥12 months, nirsevimab can be given in the deltoid muscle, as for vaccines.

Palivizumab

The dose of palivizumab is 15 mg/kg, each month, given by intramuscular injection up to 5 times during the RSV season. Consult detailed protocols from state and territory health departments or local institution guidelines for more details about using palivizumab.^14,15

Vaccine administration errors

For information on vaccine errors see Table. Clinical Guidance on RSV Immunisation Product Administration Errors.

Co-administration with other vaccines

Older adults

Older adults can receive RSV vaccines at the same time as, or separate to, other vaccines, such as COVID-19, influenza, zoster and pneumococcal vaccines. There are practical advantages of co-administration, including benefits in maximising coverage and ensuring vaccines are received on time.

Co-administration studies on RSV and influenza vaccines have shown slightly lower antibody responses to certain strains contained in the RSV vaccine and influenza vaccines compared with when these vaccines are administered separately.^16,17 The clinical significance of these decreased antibody responses is uncertain.

The likelihood of local and systemic adverse events may also increase with co-administration.^16,18 When RSV vaccine was given at the same time as adjuvanted quadrivalent influenza vaccine in clinical trials:^17,19

• local adverse events were seen in up to 53% of the co-administered group, compared with 40% when RSV vaccine was given alone
• systemic adverse events were seen in up to 45% of the co-administered group, compared with 34% when RSV vaccine was given alone

Pregnant women

Pregnant women can receive Abrysvo at the same time as, or separate to, dTpa, influenza and COVID-19 vaccines as well as Rh (D) Immunoglobulin (Anti-D). Data on co-administration in pregnant women are still emerging, but there are no theoretical concerns.

Studies on co-administration in non-pregnant women showed no safety concerns. There was a small reduction in anti-pertussis antibodies (to filamentous haemagglutinin and pertactin) when Abrysvo and dTpa vaccines were given at the same time.^17,20 However, the clinical significance of this is uncertain and no additional dTpa doses are recommended. There were no differences in the immune response to the RSV vaccine.

Infants and children

Infants and children can receive either nirsevimab or palivizumab at the same time, or separate to, routine infant and childhood vaccines and other products (such as oral or intramuscular vitamin K and hepatitis B immunoglobulin).

Co-administration data in infants and children are limited, but studies where nirsevimab was given on the same day as, or within 2 weeks of, routine childhood vaccines showed no difference in safety outcomes compared with when given separately.²¹ Because monoclonal antibodies target specific antigens, there is unlikely to be any interference with other disease antigens from vaccines or other immunisation products.²²

Interchangeability of RSV immunisation products

Abrysvo and Arexvy require only a single dose. No interchangeability is required.

A dose of nirsevimab may replace any remaining doses of palivizumab during that RSV season.

Contraindications

The only absolute contraindications to RSV vaccines are:

• anaphylaxis after a previous dose of the same RSV vaccine
• anaphylaxis after any component of an RSV vaccine

The only absolute contraindications to RSV monoclonal antibodies are:

• anaphylaxis after a previous dose of the same monoclonal antibody
• anaphylaxis after any component of a monoclonal antibody

Precautions

Women who are pregnant or breastfeeding

Abrysvo is recommended for pregnant women. See Recommendations – Women who are pregnant or breastfeeding.

Pregnant women are not recommended to receive Abrysvo earlier than 28 weeks gestation. This is a precaution while waiting for further data on adverse events of special interest, particularly the risk of preterm birth (see Other adverse events). The advice regarding gestational age at vaccination may be updated as further data become available.

If a woman has inadvertently been given Abrysvo between 24 and <28 weeks, they can be informed that safety data have indicated no statistically significant increase in adverse events compared with women who received the vaccine later in pregnancy.²³

If a woman inadvertently receives a dose of Abrysvo prior to 28 weeks gestation see Table. Clinical Guidance on RSV Immunisation Product Administration Errors.

Arexvy is not registered for use in pregnant women and should not be given to pregnant women. The data on inadvertent administration in pregnancy demonstrating potential safety concerns are limited but most reports do not describe significant adverse events.²⁴ If a pregnant woman has inadvertently been given Arexvy, do not give Abrysvo. Arexvy is expected to provide protection against RSV infection to their infant.²⁵ A dose of an RSV monoclonal antibody may be considered for their infant.

See Table. Vaccines that are routinely recommended in pregnancy: inactivated vaccines in Vaccination for women who are planning pregnancy, pregnant or breastfeeding for more details.

People with a history of Guillain–Barré syndrome

There are limited data on the risk of GBS recurrence following RSV vaccination, however, available evidence suggests recurrence of GBS is uncommon in most people with previous GBS. A United States retrospective cohort study that followed 550 individuals with a history of GBS found only six (1.1%) had a recurrent diagnosis of GBS from any cause. ²⁶

People with a history of GBS unrelated to vaccination can receive an RSV vaccine, after discussion with their provider about the risks and benefits of receiving an RSV vaccine, taking into consideration their age-related risks, medical risk factors including immunocompromise status, and personal preferences.  

People with a history of GBS within 6 weeks of vaccination may have a higher risk of GBS recurrence than if the previous GBS episode was unrelated to vaccination. They should discuss with their provider the risks and benefits of receiving an RSV vaccine.

Abrysvo

Adverse events associated with vaccination of older adults

Among clinical trial participants aged ≥60 years who received Abrysvo:²⁷

• 12% had injection site reactions, compared with 7% who received placebo. Symptoms included pain, redness and swelling at the injection site
• 28% had systemic adverse events, compared with 26% who received placebo. The most common systemic adverse events were fatigue, headache and myalgia

There was no difference in the rates of serious adverse events in participants who received Abrysvo compared with placebo.²⁷

Adverse events associated with vaccination of pregnant women

In pregnant women aged 18-49 years who received Abrysvo between 24 and 36 weeks gestation:^28,29

• 32–43% had injection site reactions, compared with 10–14% who received placebo. The most common symptom was injection site pain
• 62–63% had systemic adverse events, compared with 60–62% who received placebo. The most common symptom was fatigue

There was no difference in the rates of serious adverse events in pregnant women who received Abrysvo compared with placebo. There was also no difference in the rates of serious adverse events in the infants born to pregnant women who received Abrysvo compared with infants born to women who received placebo.^28,29

Rates of preterm birth after vaccination are being monitored (See Other adverse events of special interest (AESIs).

Arexvy

Among clinical trial participants aged ≥50 years who received Arexvy, pain was the most common injection site reaction, reported by 61% of participants aged ≥60 years (compared with 9% who received placebo)³⁰ and 75% of participants aged 50–59 years (compared with 14% who received placebo).³¹ Other injection site symptoms included redness and swelling.^30,31

The most common systemic reaction was fatigue, reported by 34% of participants of participants aged ≥60 years (compared with 16% who received placebo)³⁰and 36% of participants aged 50-59 years (compared with 19% who received placebo).³¹ Other systemic adverse events were myalgia and headache.^30,31

There was no difference in the rates of serious adverse events in participants who received Arexvy compared with placebo.^30,31

Nirsevimab

No difference in the rates of any adverse events or serious adverse events was seen in clinical trial participants aged from birth to <24 months who received nirsevimab compared with placebo or palivizumab.^21,32

Palivizumab

In clinical trial participants aged ≤2 years with haemodynamically significant congenital heart disease, no difference in the rates of any adverse events was seen in those who received palivizumab compared with placebo. The rate of any serious adverse events was significantly lower in those who received palivizumab compared with placebo (p < 0.005).³³

Adverse events of special interest (AESIs)

A very small number of AESIs (adverse events of special interest) were reported among trial participants aged ≥60 years who received Abrysvo or Arexvy. These included autoimmune inflammatory neurologic conditions such as GBS (Guillain–Barré syndrome), and atrial fibrillation.³⁴

It was difficult to determine whether the RSV vaccine caused the AESIs because:

• the number of AESIs reported in the studies were small
• some of the studies had no placebo comparator
• some of the studies involved co-administration of RSV vaccine with other vaccines

This means that establishing causality directly to the RSV vaccine was not possible.

Guillain–Barré syndrome (GBS)

Clinical trials are not statistically powered to detect rare serious adverse events, so clarification of whether these events occur at higher rates in vaccinated people than the general population requires large post-marketing surveillance studies. Early analysis of post-market surveillance data from the United States and United Kingdom in adults aged ≥60 years suggests that GBS may occur at higher rates than expected after vaccination.^35-38 Observed rates of excess cases differ for Abrysvo and Arexvy. For Abrysvo a rate of 9–18 excess GBS cases per million doses within 1–42 days after vaccination has been seen, whereas for Arexvy, a rate of 5–7 excess GBS cases per million doses within 1–42 days after vaccination has been seen. These are both higher compared with an expected rate of 2 GBS cases per million doses. The TGA has issued advice regarding the low risk of GBS following vaccination and the product information for both vaccines has been updated to list GBS as a rare AEFI. GBS remains very rare, and these findings require ongoing analyses and monitoring.

Other adverse events of special interest (AESIs)

A clinical trial of a discontinued candidate GSK RSV maternal vaccine showed an imbalance in the number of preterm births and neonatal deaths in the vaccinated group of pregnant women compared with control pregnant women groups in low- and middle-income countries.²⁵ Because of this, preterm births among pregnant women who received any RSV vaccine are being actively monitored. There was no conclusive evidence of a significant difference in preterm births in the Abrysvo trials and no imbalance was observed in a phase 3 trial of another discontinued maternal RSV vaccine candidate. But, as a precaution, the recommended lower gestational age of vaccination for Abrysvo is 28 weeks. Early studies of the risk of preterm birth in women vaccinated with Abrysvo between 32 and 36 weeks has not shown an increase in preterm birth compared to unvaccinated women.³⁹

RSV is a single-stranded RNA orthopneumovirus. RSV strains can be classified into 2 major groups: RSV A and RSV B. Strains from both groups can co-circulate each season.⁴⁰

Pathogenesis

RSV has an incubation period of 2–8 days.

RSV infects cells lining the respiratory tract, including the small airways within the lung. Infected respiratory cells eventually die, causing an increase in mucus and small airway obstruction. This presents as lower respiratory tract infection.

Severity of infection may be affected by very young or very old age, the presence of certain medical conditions (see Table. Conditions associated with increased risk of severe RSV disease in adults, and Table. Conditions associated with increased risk of severe RSV disease in infants and young children), host immune response, and viral factors.

Previous natural infection does not confer longstanding immunity and reinfection is common. Maternally derived antibody from vaccination or previous infection appears to reduce the risk of infection in young infants during the first few months of life.⁴¹

Transmission

RSV is spread in respiratory secretions by:

• contact with infected surfaces, and then transferred into the eyes or respiratory tract
• inhaling virus particles via aerosols

Viral shedding typically occurs for 7–10 days, but can continue for up to 30 days.

Primary infection with RSV, often seen in infants and young children aged 0–2 years, is generally more severe than subsequent infections at older ages.

Symptoms of RSV

RSV may present initially as an acute upper respiratory infection with:

• nasal congestion and discharge
• cough
• scratchy or sore throat
• fever
• otitis media

It may then progress to lower respiratory tract infection, which can present differently depending on age. Approximately 30–71% of infants and young children present with lower respiratory tract infection as part of the primary infection.⁴⁰

Symptoms of lower respiratory tract infection in infants and children

Infected infants often present with bronchiolitis or pneumonia characterised by:

• respiratory difficulties, with fast, laboured breathing
• wheezing
• reduced oxygen levels on saturation monitoring
• poor feeding

Older children can present with recurrence of infection, although it is less likely to progress to lower respiratory tract infection than for infants. Lower respiratory tract infection in this age group often causes wheezing and is generally milder than that seen with primary infection. RSV illness typically lasts 3–10 days in children.

Symptoms of RSV in adults

In adults, RSV typically causes an upper respiratory tract infection similar to influenza and other respiratory viruses. Typical upper respiratory tract infection symptoms are present, but RSV causes more frequent respiratory wheezing, earache and sinus pain than other viruses.⁴²

Lower respiratory tract infection can occur in adults and is associated with signs and symptoms of breathing difficulty. Bacterial co-infection is seen in approximately 30% of hospitalised patients.⁴²

Complications of RSV

In infants, apnoea or worsening oxygenation can complicate acute RSV infection. Secondary bacterial infection is relatively uncommon.

Recurrent wheezing has been commonly reported in later childhood after a diagnosis of RSV bronchiolitis in infancy. Whether severe RSV infection is causative or simply an early marker unmasking this condition remains unclear.

At all ages, worsening lower respiratory tract infection with RSV can require intensive care unit admission for respiratory support, including non-invasive or invasive mechanical ventilation.

Deaths are uncommon in immunocompetent people but can occur at the extremes of age, such as young infants or older people with frailty. However, the mortality rate associated with RSV disease can be up to 33% in people who are severely immunocompromised, such as haematopoietic stem cell transplant recipients.⁴³

People at risk of severe RSV disease

Risk factors for severe RSV disease in infants are outlined in Table. Conditions associated with increased risk of severe RSV disease in infants and young children. Some healthy children will also develop severe disease and need hospitalisation. It is difficult to predict which children may require hospitalisation.

Risk factors for severe RSV disease in adults are outlined in Table. Conditions associated with increased risk of severe RSV disease in adults.

RSV is a leading cause of lower respiratory tract infection, particularly in infants and older people. Almost all children experience RSV infection within the first 2 years of life.⁴⁰ People at increased risk of RSV infection include preterm infants, people with certain medical conditions, and Aboriginal and Torres Strait Islander people.

RSV activity varies and is primarily climate-driven. Seasonal outbreaks in most temperate regions in Australia occur during autumn and winter, usually between April and September. The season peaks during June and July,⁷ often preceding the influenza season.⁴⁴ In tropical regions, RSV seasonality can be less pronounced and may coincide with rainy seasons.^9,44-46 RSV subtypes A and B co-circulate, but one may be dominant and this may change from year to year.⁴⁷

RSV disease burden in Australia

Children aged <5 years predominantly account for RSV-associated hospitalisations, with the highest rate in infants during the first few months of life (approximately 4000 per 100,000 population aged 0–2 months, based on RSV-specific coded hospitalisations between 2016-2019). RSV-associated hospitalisation rates generally decline starting in early childhood, and begin to steadily increase in adults from the 50–65-year age cohort.^7,48

Among young children, RSV causes a disproportionately high disease burden, particularly in those born preterm. In children aged <5 years, one study showed that those born at <28 weeks gestation have a hospitalisation rate approximately 8 times higher than the overall rate, and those born at 28–31 weeks gestation have a hospitalisation rate approximately 5 times higher. 

Aboriginal and Torres Strait Islander children also have approximately 2 times higher RSV hospitalisation rates compared with non-Indigenous children.^7,8,49 At a national level, the RSV hospitalisation rate for all children including Aboriginal and Torres Strait Islander children generally falls significantly in their second year of life with lower hospitalisation rates than children aged <6 months.⁷ Data suggest that Aboriginal and Torres Strait Islander children aged 12-24 months without a risk condition have a significantly lower rate of RSV hospitalisation than all children of the same age with a risk condition.⁸ There may be regions in Australia where the rate of hospitalisation for Aboriginal and Torres Strait Islander children supports immunisation in their second year of life.⁵⁰ There are limited data on RSV disease burden in Australian older adults. Available data show a 20-fold increase in RSV-associated hospitalisation rates in adults aged ≥65 years between 2006 and 2015 compared with other adults. This is mostly attributable to increased testing and recognition of RSV in the older adult population. The burden of disease in Australian adults is likely underestimated due to infrequent testing in previous years, which is now increasing. To adjust for this possible underestimation, a study that modelled Australian RSV-attributable hospitalisations in adults aged ≥75 years showed the hospitalisation rate to be 256 per 100,000.⁴⁸

During the COVID-19 pandemic, RSV activity substantially declined and seasonality^51,52 was disrupted. However, RSV activity since the 2022–23 season in the Northern Hemisphere and 2023 season in Australia suggests a return towards a pre-pandemic seasonal pattern.⁵³

Both Arexvy and Abrysvo are protein subunit vaccines that target the prefusion configuration of the RSV F protein, which is relatively conserved among different strains of RSV.

Arexvy codes for a single prefusion F protein, which targets both RSV A and B strains, and contains the AS01E adjuvant. Abrysvo is an unadjuvanted bivalent vaccine containing prefusion F protein from both RSV A and B strains.

For both Arexvy and Abrysvo, vaccination with a single dose of RSV vaccine in clinical trials showed moderate to high efficacy in preventing RSV-associated lower respiratory tract disease among older adults during a single RSV season. Protection also extended to a 2nd season.

Abrysvo

Vaccine efficacy and effectiveness in older adults

In a large ongoing clinical trial, adults ≥60 years who received Abrysvo were 89% less likely to have an RSV-associated lower respiratory tract infection and 85% less likely to have a medically attended RSV-associated lower respiratory tract infection.^27,34

Effectiveness data from the United States, England, and Scotland showed a 62% to 92% reduction in the incidence of RSV‑related acute respiratory illness hospitalisation among older adults aged 60 years and above. In the English study, vaccine effectiveness in adults aged 75–79 years was 82% against hospitalisation for any RSV‑associated acute respiratory infections and 87% against hospitalisation for severe disease requiring oxygen supplementation.⁵⁴

In the United States study, vaccine effectiveness against RSV‑related emergency department visits and hospitalisations was similarly high, ranging from 90% to 92%, including among adults with high‑risk chronic medical conditions and those aged 75 years and older.⁵⁵  

The Scottish analysis showed a 62% reduction in the rate of RSV‑related hospitalisations among adults aged 75–79 years following programme rollout that had high uptake of 69% within the first three months.⁵⁶

Duration of immunity in older adults

After a single dose of Abrysvo, high vaccine efficacy (89%) against lower respiratory tract infection has been shown through 1 complete RSV season in the Northern and Southern Hemispheres (up to 14 months after vaccination).^27,34 Vaccine efficacy of 84% has been shown through 2 RSV seasons for Northern Hemisphere participants (up to 16 months following vaccination, with a mean follow-up of 12 months).³⁴ Vaccine efficacy during the 2nd RSV season after a single dose given before the 1st season was 79%.

Currently, data are awaited on the improvement of protection with revaccination.

Vaccine efficacy and effectiveness in infants of vaccinated pregnant women

Abrysvo is given to pregnant women to protect newborn infants against severe RSV disease by passive immunisation. For infants born to mothers who received Abrysvo, a clinical trial found vaccine efficacy of 57% against hospitalisation for RSV disease for up to 6 months. The trial also found vaccine efficacy of 70% in these infants against severe medically attended RSV-confirmed lower respiratory tract infection in their first 6 months of life.²⁹

Effectiveness data from the United Kingdom and Argentina, showed a 72% to 82% reduction in the incidence of RSV-related lower respiratory tract infection hospitalisation, among infants during their first 6 months of life.^13,57-59 In the Scottish study, vaccine effectiveness against hospitalisation in the first 3 months of life was greater for preterm infants than term infants (90% compared to 82%). Both United Kingdom studies also noted significantly reduced protection against hospitalisation for RSV disease in infants who were born less than 2 weeks after the mother received the vaccine.  A study comparing hospitalisation rates for infants born 0–14 days versus ≥14 days after their mother received the vaccine reported effectiveness of 32% compared to 82%, respectively.¹³ Although it is also likely that Abrysvo will protect pregnant women against RSV disease, no data are available on this outcome.

Duration of immunity in infants of vaccinated pregnant women

For infants born to mothers who were vaccinated with Abrysvo, protection against hospitalisation and against severe medically attended RSV-confirmed lower respiratory tract infection beyond the first 6 months of life is significantly reduced. Vaccine efficacy for RSV-confirmed hospitalisations could not be estimated in the clinical trials beyond 6 months. For severe medically attended RSV-confirmed lower respiratory tract infection, no protection was observed between 6 and 12 months.²⁹

No data are available on the duration of antibodies in women who received Abrysvo.

Arexvy

Vaccine efficacy and effectiveness in older adults

In a large clinical trial, adults aged ≥60 years who received Arexvy were 83% less likely to have RSV-associated lower respiratory tract disease and 94% less likely to have severe RSV-associated lower respiratory tract disease during the 1st RSV season after vaccination.³⁰

There is no efficacy data in adults aged 50–59 years with medical conditions, but a clinical trial showed that vaccination with Arexvy resulted in an equivalent level of neutralising antibodies compared to adults aged ≥60 years (in whom there are efficacy data) suggesting that equivalent protection was likely.²⁶

Effectiveness data from the United States showed an 83% reduction in the incidence of RSV‑related respiratory illness hospitalisation among older adults aged ≥60 years.⁶⁰

Duration of immunity in older adults

After 1 dose of Arexvy, vaccine efficacy of 83% against lower respiratory tract disease was shown during the 1st complete RSV season in the Northern Hemisphere (up to 10 months after vaccination,^27,34median of 6.7 months),³⁰ and more moderate vaccine efficacy (67%) was seen through 2 complete RSV seasons (up to a median follow-up of 17.8 months).⁶¹ Data on vaccine efficacy during the 2nd season alone after a single dose (administered before the 1st RSV season) was 56% (median follow up of 6.4 months).⁶¹ Vaccine efficacy during the 3rd season alone after a single dose (administered before the 1st RSV season) was 48% (median follow up of 7 months).⁶¹

Vaccine efficacy against severe disease after 1 dose of Arexvy was 94% during the 1st complete RSV season in the Northern Hemisphere (up to 10 months after vaccination,^27,34 median of 6.7 months).³⁰ Vaccine efficacy was 79% through 2 complete RSV seasons (median follow-up of 17.8 months),⁶¹ and efficacy of 64% was shown during the 2nd season alone against severe disease (median follow up of 6.4 months⁶¹ during season 2).

Currently, data are awaited on the improvement of protection with revaccination to guide recommendations.

Monoclonal antibody information

Both nirsevimab and palivizumab are recombinant human immunoglobulin G1 kappa (IgG1ĸ) monoclonal antibodies. They target the RSV fusion protein (F protein), but nirsevimab binds to a different antigenic site and has a modification to the Fc region that extends its half-life, making it a long-acting monoclonal antibody.^62,63 They provide protection against both the RSV A and B strains.

Nirsevimab

Efficacy and effectiveness in infants and children

A clinical trial of infants aged <12 months who were born at term or late preterm (≥35 weeks gestation) showed efficacy of 77% against both RSV hospitalisation and very severe medically attended RSV-associated lower respiratory tract infection for up to 150 days after immunisation.^11,32

Effectiveness data from Western Australia showed an 86% reduction in the incidence of RSV-related acute respiratory infection hospitalisation, among infants during their first RSV season.⁶⁴ 

Effectiveness data from Spain, France, and the United States showed a 70% to 90% reduction in the incidence of RSV-related lower respiratory tract infection hospitalisation, among infants during their first RSV season. In the same studies, there was a 67% to 92% reduction in the incidence of RSV-related ICU admission among these infants, with the observation period spanning 57–150 days.^65-74 The reported nirsevimab coverage varied across studies, ranging from 21% to 90%.

Duration of immunity in infants and children

Nirsevimab studies show protection against RSV hospitalisation to 6 months with limited evidence of protection beyond this. A trial of infants aged <12 months who were born at a gestational age of at least 29 weeks showed efficacy of 83% against RSV hospitalisation for up to 180 days.¹¹ Effectiveness data from the United States shows nirsevimab remained 77% effective against RSV-related hospitalisation at 4–7 months after administration.¹⁰

Palivizumab

Efficacy and effectiveness in infants and children

A systematic review of the clinical trials for palivizumab in preterm infants or infants aged <2 years with a risk condition showed a pooled relative risk reduction of 51% in RSV-associated hospitalisations and 50% for intensive care unit admissions compared with placebo.⁷⁵

Data from Western Australia showed 74% lower incidence of RSV infection after any dose of palivizumab compared with no dose⁴⁹ in high-risk infants aged <2 years.

Duration of immunity in infants and children

Palivizumab is a short-acting monoclonal antibody and requires monthly injections to maintain protection.

Transport according to National Vaccine Storage Guidelines: Strive for 5.⁷⁶ Store at +2°C to +8°C. Do not freeze. Protect from light.

Abrysvo and Arexvy must be reconstituted. Add the entire contents of the syringe into the vial. Gently swirl until powder is completely dissolved. Do not shake vigorously. Reconstitute immediately after taking the vaccine out of the refrigerator. After reconstitution, administer immediately or store in the refrigerator (+2°C to +8°C) or at room temperature (up to 30°C for Abrysvo or up to 25°C for Arexvy) and use within 4 hours. If it is not used within 4 hours, reconstituted vaccine must be discarded.

Nirsevimab and palivizumab must not be shaken.

Nirsevimab comes as a prefilled syringe. It may be kept at room temperature (store below 25°C) for a maximum of 8 hours. After removal from the refrigerator, nirsevimab must be used within 8 hours or discarded.

Palivizumab comes as a single use vial and should be stored in the refrigerator (+2°C to +8°C). It should be administered immediately after drawing the dose into the syringe.

RSV is a notifiable disease in all states and territories in Australia.

State and territory public health authorities can provide advice about the public health management of RSV, including management of cases and contacts.

Abrysvo

The product information for Abrysvo states it is not for active immunisation in children.

The Australian Technical Advisory Group on Immunisation (ATAGI) recommends that pregnant women of any age receive the vaccine, including those aged <18 years.

The product information for Abrysvo states the gestational age for vaccination of pregnant women is 24–36 weeks.

The Australian Technical Advisory Group on Immunisation (ATAGI) recommends that pregnant women receive the vaccine from 28 weeks. ATAGI recommends that if a pregnant woman inadvertently receives the vaccine earlier than 28 weeks gestation, a repeat dose during the same pregnancy is not needed. If pregnant women are not vaccinated before 36 weeks gestation, they can and should receive the vaccine as soon as possible. However, if it is given less than 2 weeks before giving birth, the newborn will not be adequately protected.

Beyfortus (nirsevimab)

The product information for Beyfortus states that the preferred site for administration is the anterolateral aspect of the thigh.

The Australian Technical Advisory Group on Immunisation (ATAGI) recommends that children aged ≥12 months can be given Beyfortus in the deltoid muscle.

The product information for Beyfortus states that the immunisation product is for use in infants born during or entering their first RSV season and children ≤24 months with risk conditions for severe RSV disease through their 2nd RSV season.

ATAGI recommends that Beyfortus also be used for children ≥8 to 24 months of age who are at risk of severe RSV disease entering their 2nd or subsequent RSV season.

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