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What does the evidence say about COVID-19 booster shots for everyone? What research questions about booster shots remain unanswered?

This article was published on
August 18, 2021

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SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use the video clips, audio, and comments below in news stories, with attribution to the scientist who made them.

SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use the video clips, audio, and comments below in news stories, with attribution to the scientist who made them.

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What our experts say

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Media briefing

Media Release

Expert Comments: 

Jesse L. Goodman, M.D., M.P.H.

Right now, what’s driving this consideration of booster shots is two things: One, is we’re seeing the levels of antibody that vaccinated patients have decline over time, which can sometimes signal a loss in protection. But number two, more important, we’re seeing that the protection against overall infections is also declining. What we’re not seeing yet, and remain in question, is whether this has an effect on the outcomes we’re really trying to prevent, which is hospitalization, severe disease, death. And so far vaccine protection against those more severe manifestations is holding up well.

Dorry Segev, M.D. Ph.D.

Eventually all of us will need booster shots for our COVID vaccines because the immune response we get to that vaccine decreases over time. This is called the durability of the immune response. We don’t know exactly how long the immune response will last, but we expect that at about eight months or so is when we’ll need that additional booster. Ongoing research will tell us better what that magic window is.

Ali Ellebedy, Ph.D.

The limited data sets shared by the vaccine manufacturers show that indeed a third shot substantially increases neutralizing serum antibody levels so the body can more effectively fight off the virus. However, these samples were collected within a month after that third shot, which would be the time antibody production is highest after a booster shot. Two main questions remain: First, how sustained is the increase in antibody levels? Ideally it would last six months or more. Second, would that third shot impact the spread of highly infectious variants, such as delta?

Beth Kirkpatrick, M.D.

The term ‘booster’ shot implies that the primary vaccine series was effective at making a strong protective immune response, which has waned, and now needs to be revitalized.

Evidence generally shows that the vaccines currently used in the United States remain strongly protective from severe illness, hospitalization and death, but that the mRNA vaccines may not be quite as effective as they were when first administered, especially for the delta variant. We’re seeing this in real-world data from the Pfizer and Moderna vaccine in New York, for example, as well as with the Pfizer vaccine in Israel. And although antibodies are not the only important part of immune protection, we are seeing decreasing antibody levels after full vaccination and less effectiveness of those antibodies against the delta variant. Data show that a booster dose will elevate immune responses significantly and should offer a substantially higher level of protection from infection and illness. These findings are most significant for those in the highest risk groups, including the elderly and those with high exposure, like health care workers and those in long-term care facilities. If boosters are recommended by the FDA and CDC, it is likely these groups will be targeted first.

Data that are still coming out include comparable information for the Johnson & Johnson vaccine. We also would like to understand better how well previously vaccinated individuals are protected by their immune system’s ‘memory’ and T cell responses, which may kick in to provide protection from illness even if antibody levels have dropped.

Finally, it is important to remember that this is highly dynamic, and decisions are being made with the best intentions to prevent as much illness as possible, even if complete and perfect data is not yet available. We have new information emerging continuously, paired with the current serious COVID-19 situation in United States and future changes in the virus that we cannot totally predict.

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