The Food and Drug Administration on Monday approved a Pfizer vaccine that aims to protect newborns against RSV by vaccinating pregnant people in the latter part of pregnancy.
The vaccine, Abrysvo, has also been approved for use in adults 60 and older to protect them against respiratory syncytial virus.
“Abrysvo’s approval as the first and only maternal immunization to help protect newborns immediately at birth through six months from RSV marks a significant milestone for the scientific community and for public health,” Annaliesa Anderson, Pfizer’s senior vice president and chief scientific officer for vaccine research and development, said in a statement.
Before Abrysvo can begin to be used in pregnant people, the Advisory Committee on Immunization Practices, which helps the Centers for Disease Control and Prevention set vaccination policy, must recommend the vaccine, and CDC Director Mandy Cohen must accept that recommendation. She is widely expected to do so.
The next scheduled meeting of the ACIP is set for October. But given last year’s early start to the RSV season — it peaked in November, rather than during the winter, as was normally the case before the pandemic — it is possible that a special meeting will be called in the coming days.
The vaccine is the second product designed to protect infants from RSV that the FDA has approved this summer. In July, the FDA approved Beyfortus (nirsevimab), a monoclonal antibody that should be given to infants at birth if they are born during or near the start of RSV season. Babies born at other times of the year would be given the injection near the start of RSV season. Beyfortus was developed by AstraZeneca and is marketed in the United States by Sanofi.
While Beyfortus generates protection in babies directly, the Pfizer vaccine takes an indirect approach, making use of a mechanism called passive immunity. It works by generating antibodies against RSV in pregnant individuals who are vaccinated; they in turn pass antibodies to their fetuses in the uterus. Pregnant people are vaccinated between 24 and 36 weeks of gestation.
Babies born to vaccinated people have built-in protection against severe RSV illness that should shield them from developing severe RSV in their first months of life, when they are most vulnerable. The maternal antibodies disappear over time, but the goal is to give newborns enough protection to get through their first RSV season without developing severe illness. RSV infects people of all ages, but causes the most severe illness in babies, whose airways are still developing, and in older adults.
Protecting babies’ developing airways may have additional benefits beyond preventing severe RSV.
“Could we have an effect on longer-term pulmonary conditions such as asthma? Now, I don’t suggest that we know that answer now. But I think that’s part of this larger picture that we would look to pursue to see what is the value of these types of interventions on a population basis, both nirsevimab and maternal vaccine,” Iona Munjal, Pfizer’s executive director for clinical research and development, said in an interview.
The European Medicines Agency recommended approval of this vaccine for pregnant people in July. The European Commission must formally approve the recommendation before the Pfizer vaccine will become available in Europe.
The need for tools with which to protect young children from RSV is enormous. The infection is so common that more than two-thirds of babies have been infected by their first birthday. Virtually all children will have been infected by the time they turn 2.
RSV sends about half a million children to emergency departments in the U.S. every year; somewhere between 58,000 and 80,000 of those children end up being hospitalized. That puts a huge strain on hospitals that care for children, sometimes forcing them to delay surgeries and other needed care for children during RSV season. The CDC estimates that between 100 and 300 children die from RSV in any given year.
In a Phase 3 clinical trial, the Pfizer vaccine was shown to reduce the risk of severe lower respiratory tract disease caused by RSV by 82% at three months after birth and 69% at six months.
Pfizer expects to have data next year that shows whether the antibodies generate protection that lasts into year 2 of life. But Munjal said it’s already clear that the protection from the maternal antibodies endures past six months, with vaccine efficacy of 40% for more mild RSV disease even out to a year after birth.
Abrysvo was unanimously recommended by a group of vaccine experts that advises the FDA in May. But the Vaccines and Related Biological Products Advisory Committee voiced some concerns about a possible safety signal seen with this vaccine, and with a competitor product that was eventually scrubbed.
GSK abandoned development of a maternal RSV vaccine when it detected an increased rate of preterm births among pregnant people in the vaccine arm of its Phase 3 clinical trial. Pfizer also saw an imbalance of preterm births in the vaccine arm of its trial, but the difference was not statistically significant. The rate of preterm births in both trials was below the background rate seen in the general population; still, some VRBPAC members were concerned.
The CDC’s vaccine advisers, the ACIP, have also voiced concerns about how the vaccine will be used in the real world, where disconnects between maternal health records and those of an infant may lead to some babies getting double doses of protection — in the uterus from their vaccinated parent, and after birth from an injection of Beyfortus.
Some children may need both, because they are at elevated risk of severe infection. But most would not need the two, and using both would waste financial resources and the availability of products that could help children elsewhere, experts have warned.
Another concern relates to whether the vaccine can be given at the same time as other vaccines given during pregnancy — flu shots, Covid shots, and Tdap, short for tetanus, diphtheria, and pertussis. It is known that the RSV vaccine can suppress the response to other vaccines, when they are given together — for instance the pertussis component of Tdap, or flu shots.
Munjal said in most cases the dampened immune response seen isn’t statistically significant — though it was with the pertussis vaccine. It remains to be seen what the real-world implications will be, she said.
“So what does that trend down mean? Is that actually going to manifest with any more disease? And I don’t think we know the answer to that, because you won’t know unless you do a large population rollout,” she said.
“We’ve been co-administering flu and pertussis for many, many years and pertussis and other vaccines for many, many years. We know that there’s a trend down. But ultimately, on a population basis, we’re seeing a benefit. And if you have a mom, and she’s coming for one visit, and that could be because she has kids or because things are busy, or because there’s a pandemic and she could just come in once, that could be an advantage to co-administer them.”