Fact check: New COVID-19 boosters were tested in just 8 mice? Should it matter?

RALEIGH, N.C. (WNCN) — Along with the new recipe of COVID-19 booster shots comes another claim that skeptics are using to justify their skepticism.

The new bivalent shots that target the BA.5 omicron subvariant became available last week to people 12 and older who received their initial vaccine series more than two months ago.

But were those new shots tested rigorously enough before they were injected into people?

THE CLAIM: Multiple skeptics on social media have claimed the BA.5-specific booster may be unsafe because, before humans began receiving it, it was tested on only eight mice.

THE FACTS: The basic fact is actually true — the preliminary findings presented by Pfizer were based on tests in eight mice.

What does it mean? Well, that is being blown out of proportion because experts point to several reasons why that might sound worse than it actually is.

“There’s no concern from the safety perspective that this vaccine is safe,” said Dr. Pia MacDonald, an epidemiologist at RTI International.

An earlier bivalent booster — one that targeted the BA.1 subvariant — has already found to be safe. The slight tweak to focus it on BA.5 was not nearly enough to affect how safe it is.

“They did all the studies you were supposed to do to show the safety of that, and BA.1 and BA.5 are very similar,” said Dr. David Wohl, an infectious disease expert at the University of North Carolina School of Medicine. “And so there’s really no reason to think that there should be anything different.”

The U.S. Food and Drug Administration says it bases its decision for these new bivalent vaccines in part on the clinical study of the BA.1-focused shots that are similar to the newest ones.

“We know that by just putting in a little genetic variation in the vaccine of the virus, that that does not impact on the safety of the virus because the manufacturing process is identical, minus the small amount of genetic material that is tailored to the new variant,” MacDonald said.

That process might sound familiar — the flu shots we get every year are developed the same way.

“It does not go through thousands of people going through a clinical trial,” Wohl said. “It’s engineered and designed to respond to the variant of flu that’s circulating in the world. At some point, we cannot do thousands and thousands of people (in) clinical trials for every version of the COVID-19 vaccine that comes along. At some point, you have to say, ‘Let’s stop it, trust the science, trust the technology and move on,’ and just use the same construct but tweak it. And that’s exactly what’s happening.”

The newest boosters are coming along at a time when the vaccination effort — in both North Carolina and beyond — has slowed to a crawl.

Just over 5,000 booster doses were given between Aug. 31 and Sept. 7, according to data from the state Department of Health and Human Services. Not only is that the fewest since the agency went to a weekly reporting schedule, it’s less than half of the previous weekly low total.

Wohl says he expects the new boosters to send those numbers back up.

“Now we have a vaccine that protects us against the variant, the virus that’s circulating right now,” Wohl said. “Up until this point, we’ve been stuck. We’ve caught up. And I expect the same sort of responses that we saw originally against the Wuhan strain from the original vaccines, against BA.5 with these new vaccines.”