3 things to know about COVID-19 vaccine boosters

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Now that about 43 percent of the U.S. population has been fully vaccinated, talk of COVID-19 vaccine booster doses is rising. 

Three notes on booster shots: 

1. The big question is when, not if, boosters are needed. How long does strong protection from COVID-19 vaccination last? That's the key question lingering in researchers' minds. What's certain is that it won't last forever, pointing to the need for booster shots at some point. 

"When it starts to taper off, then we'll seriously consider needing a booster," Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, told theGrio in a story published June 9. Since COVID-19 vaccines only became available in December, that's been hard to assess. 

Early findings, however, indicate strong protection will last for at least a year. Two recent studies suggest people who've been vaccinated on top of having recovered from a natural COVID-19 infection may have even more durable immunity. The first study, published in Nature May 24, involved 77 people who were infected with COVID-19 about a year earlier and had since recovered. They found memory B cells lingered in the bone marrow, ready to produce bone antibodies as needed in the months after infection. 

The second study, published in the pre-print server bioRxiv, included 63 people who also recovered from the virus. Findings showed their memory B cells evolved and strengthened over time, with the antibodies they produced able to neutralize some of the virus variants. The neutralizing ability was greatest among those who had received at least their first vaccine dose. 

While additional studies are ongoing and official recommendations from national agencies have yet to be made, vaccine makers are preparing to have booster doses ready by fall. 

2. Booster doses could be one of three options: The same shot a person initially received, a shot from a different vaccine maker, or a vaccine adjusted to target a specific variant. 

The National Institutes of Health has launched an early stage clinical trial to test a mix-and-match approach to COVID-19 vaccine boosters. As part of the trial, people who were initially vaccinated with either Johnson & Johnson, Moderna, or Pfizer-BioNTech's dose regimen will all receive one booster dose of Moderna's shot 12 to 20 weeks later. 

"The results of this trial are intended to inform public health policy decisions on the potential use of mixed vaccine schedules should booster doses be indicated," Dr. Fauci said. 

Based on research from other diseases, experts anticipate a mix-and-match approach will generate a greater immune response to booster doses. 

"This is a tried and true concept from before COVID-19, " Kirsten Lyke, MD, principal investigator of the NIH's booster trial and professor of medicine at the University of Maryland in Baltimore, told The New York Times. 

If trial results indicate this approach is safe and effective, it could ease the logistics of a booster rollout since people wouldn't be limited to the same shot they received for their initial regimen. 

While vaccine makers have said they have the ability to quickly make adjustments to their original shots to target a particular variant, that likely won't be necessary — at least not yet. 

"Instead of having to play whack-a-mole with each individual variant and developing a booster that's variant-specific, it is likely that you could just keep boosting against the wild type, and wind up getting a good enough response that you wouldn't have to worry about the variants," Dr. Fauci told CNN

Studies have also suggested existing vaccines provide at least some protection against variants. For example, Pfizer's vaccine was 87 percent to 89.5 percent effective at preventing infection caused by the alpha variant, first detected in the U.K., and 72.1 percent to 75 percent effective against the beta variant, first detected in South Africa. 

Vaccines also appear effective against the delta variant, which has wreaked havoc in India. Pfizer's vaccine appeared to be 88 percent effective against symptomatic disease from the variant in a recent U.K. study

3. A spike in hospitalizations would signal an immediate need for boosters, experts told U.S. News & World Report. 

Vaccine immunity won't disappear overnight, and waning immunity doesn't necessarily serve as the sole factor in determining the need for boosters. 

Keeping an eye on the number and severity of breakthrough COVID-19 cases, or infections after vaccination, is also a telling sign. 

"If the immunity induced by vaccines is waning to the point that you're no longer getting protection against significant disease, then that would be a driver for boosters," Anna Durbin, MD, professor at Johns Hopkins Bloomberg School of Public Health in Baltimore, told the news outlet. 

"If every breakthrough case is asymptomatic, and we're not seeing the emergence of more virulent variants … we would know we have enough immunity to protect ourselves from significant illness." 

If hospitalizations among vaccinated people began to rise however, that would indicate a wider, more immediate need for booster doses, Dr. Durbin said. 


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