Pfizer’s RSV vaccine, given during pregnancy, protects infants from severe disease

Pfizer’s RSV vaccine, given during pregnancy, protects infants from severe disease

Pfizer’s RSV vaccine, given during pregnancy, protects infants from severe disease


Pfizer announced Tuesday that its RSV vaccine given to mothers during pregnancy protected infants from developing severe symptoms during the first six months after birth — a critical window of vulnerability.

The company plans to file for approval of the vaccine before the end of the year, with hopes that the shot could be the first to help protect infants against RSV — the respiratory syncytial virus — as early as next winter.

The data was released in a press release and has not yet been published or reviewed. But it offers a glimmer of good news amid a brutal and early RSV season that has contributed to the wave of respiratory illnesses that have overwhelming many pediatric hospitals.

“We are very hopeful that everything can be done in time to vaccinate mothers before the next RSV season,” said Annaliesa Anderson, chief scientific officer of vaccine research and development at Pfizer. “We are entering a very difficult RSV season. We see hospitals filling up. Everyone appreciates the urgency that can really help prevent that.”

RSV is a common respiratory illness, and most people experience it as cold-like symptoms. But in young infants, whose airways are smaller, the virus can be life-threatening — and is the leading cause of hospitalization for babies.

Decades of fear and failure in the search for an RSV vaccine. Now, success.

Unlike vaccines that are given directly to infants, Pfizer’s shot provides protection indirectly. Antibodies are naturally transferred to infants during pregnancy, so maternal vaccination is a way to give babies a temporary, but immediate, shield of immune protection. Influenza, diphtheria, tetanus and pertussis vaccines are also given as immunizations for mothers.

Pfizer’s vaccine, given early in the third trimester, was 69 percent effective after birth in preventing severe cases of the disease that required medical attention for six months. It was even more effective within the first three months after birth, possibly reflecting antibody levels that naturally decline over time.

The researchers also measured whether the vaccine prevented RSV-related doctor visits in infants, including cases that were not serious. These results did not reach statistical significance, but suggest that the vaccine could cut RSV doctor visits in half during the first six months after birth.

The company said there were no major safety concerns for babies or vaccinated people, but that regulators would scrutinize the data. 7,400 pregnant women participated in the study, and the infants were monitored for at least one year.

Barney Grahama vaccine expert at Morehouse School of Medicine whose work with Jason McLellan at the University of Texas at Austin underlies much of the progress in the RSV field, said the news was encouraging.

“I think this is a big step for protecting babies from RSV and improving overall lung health,” Graham said. “Overall, this is an exciting time for RSV. It’s also a worrying time, because you see how covid has changed the patterns of infection, and this year we have an earlier, bigger season than we’ve had in a few years — and it’s causing a lot of hospitalizations and misery for people.”

Two promising tools to prevent RSV in infants could soon be available, if regulators agree they are safe and effective. With Pfizer’s maternal vaccine, AstraZeneca and Sanofi have shown that a single dose of a monoclonal antibody can protect infants against RSV for five months. That drug nirsivamab, was recently recommended for approval in Europe. Two vaccines for the elderly have also shown success, from Pfizer and GSK.

Many pediatricians have been waiting decades for tools to combat RSV. Early attempts to create a vaccine had disastrous results, causing babies to develop heightened disease if infected and casting a shadow over the field.

If both a preventive monoclonal antibody treatment and a vaccine soon become available, it will give doctors options — and lead to debates about how the various tools should be used.

“I’m so thrilled with where the field is at the moment. I think there are many, many people in the world who share my excitement,” said Ruth Karron, a pediatrician and professor of international health at the Johns Hopkins Bloomberg School of Public Health, who is working on a different vaccine that could be given directly to young children, to protect them after the first six months.

“The difference this year is that for the first time, the general public is probably eagerly anticipating an RSV vaccine, because they’re seeing firsthand how much of a problem RSV can be.”


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