RSV is a common seasonal respiratory virus that pretty much everyone gets infected with multiple times over the course of their life, and those infections start early. Almost all children get it before they turn 2. All that might make it sound somewhat harmless.

After all, if we've all been infected multiple times and live to tell the tale, it must be a pretty survivable situation, no? Well, no. Not for everyone, anyway.

Elderly populations, people with compromised immune systems, and infants can be severely affected by RSV. According to the CDC, RSV is responsible for between 60,000 to 160,000 hospitalizations among older adults in the United States alone, with an associated 6,000 to 10,000 annual deaths. Between 55,000 and 200,000 yearly deaths are estimated to occur in children under five years of age due to the virus. It is also the leading cause of hospitalization for infants, and can lead to later development of asthma. 

Scientists have long been in hot pursuit of an RSV vaccine. And as of May 3rd, 2023, the US Food and Drug Administration approved the very first one-- well, technically the first, but we'll get to that in a minute. It's called Arexvy, and it is currently approved for use in people 60 years of age or older.

Approval was given based on data from a Phase 3 clinical trial with 35,000 participants, half of whom received a placebo, and half of whom received the vaccine. The results of the trial were impressive-- the vaccine reduced the risk of RSV-associated lower respiratory tract disease by almost 83%, and reduced the risk of severe disease by just over 94%. The most common side effects were fairly minor, though further monitoring for atrial fibrillation (an irregular and rapid heartbeat) will be conducted after the vaccine becomes available.

This side effect was reported in 4 participants within 30 days of taking the placebo, and in 10 participants within 30 days of taking the vaccine. Because the number was higher in the vaccine group, the post-market monitoring will be necessary to determine if this is a rare side effect of the vaccine.  What about the babies, you may be asking. As I mentioned previously, there is technically a vaccine available for infants, but it is only for pre-term infants less than 6 months old, and it's essentially a shot of RSV antibodies that must be given monthly.

To protect healthy, full-term infants, scientists have pursued a vaccine that could be given during pregnancy to protect the infant. While mothers can already pass on antibodies to their infants, that protection only lasts a few weeks. So a Phase 3 clinical trial administered the adult RSV vaccine or a placebo to approximately 3700 pregnant women each, and the results were enough to garner approval from an FDA vaccine advisory council.  Trial results suggest that the risk of severe disease was reduced by 82% in the first three months of life for infants whose mothers received the vaccine, and by 64% by six months of age.

There was a small concern about preterm birth, which occurred at around 5.7% in the vaccinated group, compared to 4.7% in the placebo group. This is a small difference that could be due to chance, but it could also be an issue that can only be confirmed with a larger data set. Should the vaccine gain full approval, this will almost certainly be a focus of post-market monitoring.

Now is a good time to mention that an RSV vaccine  for infants was approved for use in Europe in 2022 and is now under review by the FDA. It's unclear which vaccine will get a decision first-- this infant one or the maternal one we just covered-- but it's nice that we got options. This is pretty exciting news, and it could reduce a lot of severe disease and death among vulnerable populations with what looked to be either minor or rare side effects, and that's a big public health win.

Hey did you enjoy this episode? You might enjoy this previous series from 2020 on the history, present, and future of vaccines. We'd appreciate it if you'd like the video, subscribe to the channel down below, and consider going to patreon.com/HealthcareTriage where you can help support the show, make it bigger and better.

We'd like to especially thank our research associates, Joe Sevits, Edward Liljeholm, and of course, our surgeon admiral Sam.