An update on RSV vaccines. Where do we stand?

From a major failure in the 1960s to a recent possible success, we may be close to the goal of preventing a lot of serious illness.

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RSV is everywhere. It is hospitalizing thousands infants and children to be sure, though mostly it is just making everyone miserable, and causing a lot of suffering, and countless missed days of school.

In the coming week, I plan to write about why we are having such a bad RSV season, tackling the concepts of “immunity debt” or “immunity catch-up.” But today, I’m writing a quick dispatch about RSV vaccines.

Why is there not an RSV vaccine? The short answer is that the science and medical communities have a kind of PTSD from an RSV vaccine trial that went badly decades ago. In the 1960s, an RSV vaccine candidate backfired. In infants who got infected with RSV after they were vaccinated, apparently more severe (and even two fatal) outcomes occurred. Failures like these often take years if not decades to recover from.

Is there an RSV vaccine on the horizon? Yes! Scientists have sorted out what went wrong last century, and have developed new and improved approaches. Last month, Pfizer announced favorable results on a new RSV vaccine candidate being tested in a Phase 3 clinical trial.

Per a Pfizer press release, “Vaccine efficacy of 81.8% was observed against severe medically attended lower respiratory tract illness due to RSV in infants from birth through the first 90 days of life with high efficacy of 69.4% demonstrated through the first six months of life.”

In short, researchers achieved one of their major objectives—preventing severe respiratory illnesses—although it seems like they did not achieve as high a rate of success on decreasing medical visits over all.

Still, this is promising and Pfizer is seeking regulatory approval based on the data they have. As usual, we’ll need to see much more information before saying anything definitive. But this early look—including indications the vaccines have been found to be safe—is reason for optimism.

Overall, the Pfizer strategies seem good. First, decreasing severe disease should be the top priority, by a substantial margin. Decreasing all illness would be nice, but we should not let the pursuit of something perfect dissuade us from getting something that is very good. Second, vaccinating pregnant people (the study did not actually test the vaccine on infants, although eventually that should be looked at too) is a savvy approach. We know that when mothers who are pregnant get vaccinated against other pathogens (such as tetanus, pertussis, diphtheria, influenza, SARS-CoV-2, etc), the antibodies created are transferred through the placenta to their fetuses. This passively gives the eventual newborns and infants a degree of immunity lasting several months, reducing the odds of severe disease at an extremely vulnerable time of life. In fact, it was on this basis that two colleagues and I recently made the case for additional boosters for pregnant people during the 2nd half of pregnancy.

So, when will we know more and when will the FDA make any decisions? If Covid-19 taught us anything about vaccine development, it’s that the FDA can move quickly when needed. RSV is clearly an emergency situation for the pediatric population. That means the FDA should move as quickly as possible. But the FDA has to balance the urgency to act with the need for rigor. Both safety and efficacy have to be ironclad. Setbacks can be devastating and we can’t afford another failure like we had with the 1960s RSV vaccine. That said, things are looking promising. Pfizer plans to submit its application to the FDA by the end of 2022.

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Inside Medicine is written five days per week by Dr. Jeremy Faust, MD, MS, a practicing emergency physician, a public health researcher, and a writer. He blends his frontline clinical experience with original and incisive analyses of emerging data—and to help people make sense of complicated and important issues.

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