The Biden administration’s push for COVID-19 booster shots has led to questions about why additional doses wouldn’t specifically target the delta strain now ravaging parts of the country.
“Anyone else frustrated that boosters will be the original vaccine?” Dr. Michael Mina, an epidemiologist at Harvard T.H. Chan School of Public Health, wrote on Twitter. “Why push for a vaccine that is already outdated. If we are going to boost — use a delta variant of the vaccine. Delta is our baseline now.”
The idea of a delta variant vaccine booster would be particularly viable because of the mRNA technology used to create the Pfizer-BioNTech and Moderna vaccines. Such vaccines “can be adapted quickly,” Mina noted. In fact, Moderna designed its initial mRNA vaccine in about two days.
But Dr. Larry Corey, professor of the vaccine and infectious disease division at the Fred Hutchinson Cancer Research Center, said it might not be that simple.
“It sounds good that if you matched [the booster with the variant], it would be better, but that actually has not been proven,” Corey said. “Even against the more resistant variants, it may be that just having more antibodies is all that’s required.”
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Israel is one of the countries struggling with the delta variant. A recent study from Israel followed those 60 and older who received a Pfizer booster shot based on the original strain of the virus from July to August. It found an 11-fold decrease in the risk against COVID-19 infection and a 10-fold decrease in the risk of developing severe illness among those who received a booster.
Designing the delta-specific booster would only be the first step. Vaccine makers would still need to test a delta booster to determine its safety and efficacy. Both Pfizer and Moderna began tests for a booster of their original vaccines earlier this year.
The Food and Drug Administration does not require additional testing for a booster based on a variant like delta to determine its efficacy. However, the agency does say a vaccine maker should.
“Would you think it would be better to wait six months or eight months for a delta booster versus taking a booster of the original strain now that pushes your antibodies up to levels that, you know, knocks your socks off?” Corey said. “We know the vaccine for the original strain is safe. It’s in the bottle, and we know everything about it.”
An extra three to six months could prove costly as recent studies have shown the antibody protection from the first doses of a COVID-19 vaccine may begin to wane after four to five months.
Corey also noted there is no guarantee a delta booster would work better than a booster based on the original strain.
As of yet, there is no research on a variant-based booster in humans. Vaccine maker Novavax has developed a booster that targets the beta variant. Also known as B.1.351, the beta variant is thought to be 50% more infectious than the original strain, and earlier in the year, it was the predominant strain in South Africa.
Novavax said in a recent press release that testing of its booster in baboons caused a strong response against the beta variant but did not release specific numbers.
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However, the Novavax booster might not provide much extra protection against the beta variant than a regular COVID-19 vaccine. An Israeli study found the Pfizer vaccine displayed 94% efficacy in humans against the beta variant.
