What if my second vaccine dose is early or delayed? Here’s what the CDC says

A person gets a vaccine shot.
The CDC has set guidelines on the best time frame to get a second vaccine dose.
(David Goldman / Associated Press)

There’s a lot of confusion out there about second doses of the COVID-19 vaccine.

The COVID-19 vaccine rollout has been chaotic in California. Guidance on how to get the second dose has changed from “you have to make your own appointment” to “we’ll tell you when to come back” to “OK, you should hear from us, but if you don’t, just come back.” The Los Angeles County department of public health admitted on Twitter that it had been stressful.

People are also concerned about the timing of the second dose. Over at the L.A. Times tip line, we’ve been getting inquiries about second dose appointments that are not precisely timed after the first.

In its clinical trials, Pfizer administered the second dose 21 days after the first. For Moderna, it was 28 days. According to the U.S. Centers for Disease Control and Prevention, the second dose should be administered as close to the recommended date as possible. But total precision isn’t required.


If it’s a little earlier, that’s allowed: “Second doses administered within a grace period of four days earlier than the recommended date for the second dose are still considered valid,” the CDC says on its website.

A couple of weeks later is fine too. “If it is not feasible to adhere to the recommended interval and a delay in vaccination is unavoidable, the second dose of Pfizer-BioNTech and Moderna COVID-19 vaccines may be administered up to six weeks (42 days) after the first dose.”

California is reserving large amounts of COVID-19 vaccine supply for people needing their second dose, leaving fewer first doses available.

Feb. 9, 2021

Dr. Diane Griffin is a virologist at the Johns Hopkins Bloomberg School of Public Health who studies immune responses to viral infections and vaccines. She said in an interview with The Times that while there aren’t studies of the efficacy of these vaccines when the second dose isn’t administered right on schedule, based on what we do know about other vaccines and immune responses, there’s no reason it won’t work just as well.

“I think that perfection is the enemy of the good,” she said.

In other words: Don’t stress about your second dose being a little early or late. The important thing is that you get it.

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Staff writer Amina Khan contributed to this report.


The process for getting a COVID-19 vaccine varies county to county.

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