Answering your COVID questions: 'Is there a difference between the first and second vaccine doses?'

Posted at 6:32 PM, Feb 16, 2021
and last updated 2021-02-16 20:30:45-05

Currently, both the Pfizer and Moderna COVID-19 vaccines require two shots to be fully effective.

Is there a difference between the first and second COVID-19 vaccine doses?

WCPO viewer Marilyn Kaylor asks on Facebook: “Are the components of the first dose of the vaccine the same as the components of the second dose? In other words, can a vial of vaccine be used for a first dose or a second dose?”

Both doses are exactly the same, according to Dr. Steve Feagins of Mercy Health and medical director of Hamilton County Public Health.

“In fact, it's now very common that you may see someone in line who's getting the first dose followed by someone getting the second dose,” he said. “They are exactly the same.”

So, if doses are the same, why are some people reporting having a reaction to the second dose with things like fever, aches and other minor side effects? Feagins said he, too, had a fever after his second dose of vaccine.

“The first dose primes the second dose, causing more antibodies and a more vigorous response for more prolonged antibody protection,” Feagins said. “So, yeah, the actual doses are the same, but the responses can and should be more robust after you get the second one. If you got a third dose, it might be even more robust."

Johnson & Johnson’s vaccine, which requires only one shot, has not yet been authorized for emergency use in the U.S.

This month, WCPO 9 is taking your questions about COVID-19 vaccines and posing them to local health care experts. Email or message @KristynHartmanWCPO on Facebook with your name, neighborhood and question, and you could see an expert answer it on air.