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What happens if you miss your second dose of the vaccine?

FILE - In this Jan. 18, 2021, file photo, a vial of the Pfizer-BioNTech vaccine against COVID-19 is prepared at a vaccination center of the 3rd district, in Paris. (AP Photo/Francois Mori, File)

(NEXSTAR) — The Centers for Disease Control and Prevention recommend receiving your second COVID-19 vaccine dose three weeks after getting the first dose of the Pfizer vaccine and one month after receiving the first Moderna shot.

But what happens if you miss your second vaccine appointment?

Don’t sweat — but act quickly to reschedule a second dose.

While the CDC recommends people get their second dose “as close to the recommended interval as possible,” there is a small grace period, a CDC spokesperson told Nexstar.

If you get your dose four days early, that’s okay, the agency said.

If you miss your second vaccine dose, you can receive it up to six weeks after the first dose, for both the Pfizer and Moderna vaccines.

Why must you wait an interval to get your second dose? The Advisory Committee on Immunization Practices recommends the doses be spaced apart based off of clinical trials.

“These trials have shown the most efficacy in mRNA vaccines with the recommended two doses,” the CDC said.

After the first dose, you’re only somewhat protected from COVID. 

Studies have shown that a single shot of the Pfizer vaccine is 52-percent effective at preventing COVID-19 infection. 

The Moderna vaccine is thought to be 80.2-percent effective after a single dose, according to a document the vaccine manufacturer submitted to the FDA. 

After receiving two doses of either shot — and waiting two weeks for the second dose to kick in — you should be 95-percent protected from COVID-19.