Understanding the new recommendations on COVID-19 boosters

Eric Rubin
Eric Rubin

September 21, 2021—Eric Rubin, adjunct professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health and editor-in-chief of the New England Journal of Medicine, is a temporary voting member of the U.S. Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee. In this Q&A, he discusses the committee’s vote on September 17 to recommend that people age 65 and older, those at risk of developing severe disease, and people in high-risk occupations receive a booster dose of Pfizer-BioNTech’s COVID-19 vaccine, but not people in the general population aged 16-64.

Q: Some have expressed dismay that the committee did not recommend boosters to a broader population, including some governors whose states are struggling with the pandemic during the Delta surge. Why were members so firm on this, given that data from Israel seem to suggest that a third shot helps prevent infection?

A: Let me start with the most important point. The vaccines work and they even work during the time when the Delta variant is prevalent, though perhaps not quite as well. The most important way that people can decrease their own risk is to get a full series of one of the vaccines. A third dose might help, but not nearly as much as getting vaccinated in the first place.

I can’t speak for everyone on the committee, but I suspect that there were three major concerns. First, the data on effectiveness are very new. We don’t know how long an extra shot will last. Second, the best safety data available are from Israel, though only through observations rather than a controlled trial. As of the time that the data were reviewed, there was very little to provide reassurance that a third dose will be sufficiently safe in younger people to justify the smaller benefit (as younger people are less likely to develop severe illness). Finally, we don’t know that a third dose reduces the risk of transmitting infection. Israel is banking on this. But the situation in Israel is different from the U.S. In Israel, where vaccination rates are high, even a small reduction in transmission could have important public health benefits. In the U.S., with a large unvaccinated population, reducing transmission from vaccinated individuals just won’t have that much of an impact.

Despite all of that, the data are coming out rapidly. With more data, I wouldn’t be surprised if recommendations on boosters change fairly soon.

Q:  Why did the committee think it was important to cover certain groups with a booster?

A: One of the motivations for Israel to give booster doses is to reduce the size of the epidemic. Here in the U.S., where boosters are less likely to have an effect on the overall epidemic, it’s probably more important to reduce the risk of severe disease. The safety data are pretty compelling for the reduction in serious illness in older individuals and other high-risk individuals.

Q:  A recent U.S. study showed that the Moderna vaccine appears to be more effective than the Pfizer vaccine. Should people who got a Pfizer vaccine opt for a Moderna booster if one become available?

Again, the important message is that all of the vaccines given in the U.S. work. As time goes on we’re likely to find differences in their effectiveness and durability. But the differences are much more subtle than the commonalities. I got Pfizer and I’m not worried.

Q: Is there any other important information about boosters that you think the public should know about at this time?

A: It’s sometimes hard to see conflicting advice even from sources that we trust. But, since what we know is rapidly changing, we should expect that recommendations will similarly change rapidly. Not everything we’ve done in the past has proven to be right and that will continue to be the case going forward. But, overall, the guidance from the CDC [Centers for Disease Control and Prevention] and other public health authorities helped. We do have many tools to help keep people safe during the epidemic. It will take time to figure out how best to use them.

Amy Roeder