Three vaccines against respiratory syncytial virus (RSV) are currently undergoing review by the Therapeutic Goods Administration, as the roll-out of GSK’s Arexvy and Pfizer’s Abrysvo is set to begin for older adults in the United States in the coming weeks.
The two vaccines were approved for people 60 and older by the US Food and Drug Administration earlier this year, and in July, Moderna began the authorisation process for its own RSV vaccine in multiple jurisdictions including Australia.
In Europe, Pfizer’s vaccine Abrysvo has also been approved for passive immunisation of infants from birth through 6 months of age via pregnant women.
RSV is highly contagious and while healthy adults typically have mild cold-like symptoms, it can cause serious complications including lower respiratory tract infection, which can then cause life threatening illnesses as pneumonia and bronchiolitis.
Associate Professor Michael Woodward, a geriatrician and Director of Aged Care Research at Austin Health in Melbourne, says COVID-19 era restrictions that had limited the spread of virus have now contributed to a longer and more severe RSV season.
He says the extent of the current RSV outbreak highlights the urgency of a vaccine.
“As the current outbreak has shown, RSV can have serious consequences when it sweeps through the community, so getting a vaccine authorised in Australia is a priority.”
Although incidence of hospitalisation and mortality is much higher in adults aged 65 and older, RSV was the leading cause of hospitalisation of infants in the US in 2022, according to data from the National Foundation for Infectious Diseases.
Since RSV became notifiable in Australia in 2021, case rates have skyrocketed, with some states reporting 10 times the rate in 2022 compared to the previous year, but Associate Professor Woodward says it’s still under-recognised and under-tested in Australia.
How do the vaccines work?
The GSK and Pfizer vaccines both work by inducing antibody production against the pre-fusion F protein (known as RSV F glycoprotein), which is found on the surface of the virus. This prevents the RSV virus from fusing with the target cell.
Moderna’s vaccine is an mRNA vaccine that also induces antibodies against the same pre-fusion F-protein.
Both Arexvyand Abrysvo have been approved in the US for the prevention of lower respiratory tract disease, the most serious complication of RSV. Associate Professor Woodward says efficacy is measured by a reduction in RSV-associated lower respiratory tract illness—and he says it’s encouragingly high. He notes that Moderna has also completed its clinical trials, reporting similar efficacy.
“With 80% efficacy against lower respiratory tract disease, RSV vaccines are more effective than both the flu and pneumococcal vaccines,” he says.
Importantly, vaccination is particularly effective against severe RSV-associated lower respiratory tract infection (LRTD), with Arexvy and Abrysvo demonstrating 94% and 86% reduction, respectively.
The US Centers for Disease Control and Prevention(CDC) says both the GSK and Pfizer vaccines demonstrated moderate to high efficacy in preventing symptomatic RSV-associated LRTD over two consecutive seasons among adults who are 60 or older.
“Although trials were underpowered to estimate efficacy against RSV-associated hospitalization and death, prevention of LRTD, including medically attended LRTD, suggests that vaccination might prevent considerable morbidity from RSV disease among adults aged ≥60 years,” the CDC rationale for recommendations explains.
While serious side effects appear to be rare, the FDA has required GSK to conduct a post-marketing study to assess the risks of Guillain-Barré syndrome after one study participant developed the disease, and acute disseminated encephalomyelitis after two participants developed the disease after receiving the vaccine concomitantly with a flu vaccine.
The FDA is also requiring Pfizer to conduct a post-marketing study, reporting on adverse experience for Guillain-Barré Syndrome (GBS) and other immune-mediated demyelinating conditions, and supraventricular arrythmias, as part of its license.
The CDC explained that “Although both vaccines were generally well-tolerated with an acceptable safety profile, six cases of inflammatory neurologic events were reported after RSV vaccination in clinical trials. Whether these events occurred due to chance, or whether RSV vaccination increases the risk for inflammatory neurologic events is currently unknown.” Until evidence becomes available from post-marketing surveillance to clarify this, the CDC says RSV vaccination should be targeted at those who are at highest risk for severe disease, and therefore most likely to benefit.
It is unclear at this stage whether Moderna will also be required to conduct a post-marketing study, since it has not been approved yet. Associate Professor Woodward says he is not aware of any additional myocarditis risk associated with the Moderna vaccine, which uses mRNA technology.
Associate Professor Woodward says vaccines are likely to be authorised in the next 12 months, and listed on the National Immunisation Program for people aged 60 and older and those with compromised immunity and other medical conditions.
He says that as soon as the vaccines are approved GPs should discuss vaccination with their patients who are 60 or older and those who are immune compromised or have multiple chronic diseases.
Trial results suggest the vaccines will protect for the entire RSV season, with efficacy still high at six to seven months, but it isn’t yet clear how long they’ll remain effective or whether further vaccination will be required.
In the short term, Associate Professor Woodward says the most important thing once a vaccine is approved will be “to get the vaccine into the arm.”
In the meantime, he says routine testing is needed to better understand the overall burden of RSV in adults, and to help better care for older adults with RSV.
“PCR testing is best,” Associate Professor Woodward says. “Rapid antigen testing is much less accurate and viral culture is generally only performed in surveillance/research settings.”
For a much more detailed update on RSV and the vaccines—and up to 17 hours of CPD, register here to attend the 2023 Medical Update in Melbourne (2 September) or Sydney (9 September).
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