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One dose? Two? A booster? The science behind COVID-19 vaccine dosing

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Posted at 4:28 PM, Mar 03, 2021
and last updated 2021-03-04 11:17:33-05

(WXYZ)  — On Friday the FDA authorized their third COVID-19 vaccine for emergency use: one-shot by Johnson & Johnson. The news was celebrated as another step towards vaccine access and herd immunity, but it also raised questions about dosage. Why do some vaccines like Moderna and Pfizer require two shots while J&J is only approved for one?

"There was a fair amount of discussion at the vaccine approvals about the one dose versus two doses," said University of Michigan epidemiologist Dr. Arnold Monto, who chairs the FDA Vaccine Advisory Committee. "I had to say that was not relevant because we were asked to approve a one-dose strategy, and we approved what was put in front of us."

According to Monto, even though the single-shot vaccine is now approved, Johnson & Johnson is in the midst of a two-shot trial. This could change recommendations down the road.

"We’re in a place now where we have to make some decisions based on imperfect information," said Monto, explaining that while the FDA waits for the results of the two-shot study it made sense to approve the one-shot dose which has been shown to be 72% effective against moderate and severe cases of COVID in the United States.

"You can always go and get a second dose of the Johnson & Johnson vaccine if it proves to be better with two doses," he said.

The idea of dosing as a moving target is not unique to Johnson & Johnson. Last week Pfizer announced that it was starting a study looking into the efficacy of a third booster shot. A move in response to the new variants spreading across the globe.

But still, as the dosing is being figured out doctors are encouraging individuals to take advantage of what is out there.

"Any one of them is just so amazingly effective, and nobody anticipated we’d have vaccines that worked so well against this," said Dr. William Petri, an immunologist at the University of Virginia.

As the US deals with shortages and struggles to distribute the vaccine Petri raises the point of the UK approach: Get everyone one-shot first.

"Let’s try to get everybody get at least one dose of the vaccine," said Petri. "We know one dose of the vaccine is incredibly effective."

While this idea may be appealing to some, this week Dr. Anthony Fauci said the U.S. would be sticking to its current strategy — dosing as the FDA approved.

"I’m just really thankful we have three just to get things delivered to people," said Petri.

Michigan is set to get 82,700 Johnson & Johnson vaccines this week. Currently, 15% of the state has received at least one shot of Moderna or Pfizer.