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Do You Have To Get Your Second COVID-19 Shot Exactly 21 Or 28 Days After Your First?

A vial of the COVID-19 vaccine Pfizer BioNTech provided to healthcare workers at Dell Medical School on Dec. 15, 2020. (Gabriel C. Pérez/KUT News)
A vial of the COVID-19 vaccine Pfizer BioNTech provided to healthcare workers at Dell Medical School on Dec. 15, 2020. (Gabriel C. Pérez/KUT News)

QUESTION: Is it necessary to get the second shot exactly 21 or 28 days later, or is it at least that amount? What if something comes up and you can't make it for the second shot on exactly that day? — Susan

ANSWER: No, you do not need to get the second shot exactly 21 or 28 days after the first. The Centers for Disease Control and Prevention says you can get the second dose later than the recommended interval, but you shouldn’t get it any sooner.

The two COVID-19 vaccines approved in the U.S. right now require two doses for full protection. Pfizer-BioNTech’s vaccine calls for a second dose 21 days after the first, and Moderna’s calls for the second dose 28 days later.

If you can’t schedule an appointment exactly 21 or 28 days from your first appointment, that's OK. "There is no maximum interval between the fist and second doses for either vaccine,” according to the CDC. But the agency does urge people to get the second shot as close to those timeframes as possible so they can get full protection as soon as possible.

After getting the second dose, health experts warn, you won’t immediately be fully immune. It takes time for your body to build up immunity, and the vaccine may not protect you until one or two weeks after the second shot, the CDC says.

You don’t have to go to the same provider you went to the first time to get your second shot, says the Texas Department of State Health Services, but your provider should receive a second dose for you. If for some reason you don’t go to the same provider, make sure your second shot is from the same manufacturer as the first. Your provider should give you information about what vaccine you got and when you should come back for a second dose, DSHS says.

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