COVID-19 Vaccine Tracker
COVID Questions
April 7, 2021 1:13 PM EDT

Welcome to COVID Questions, TIME’s advice column. We’re trying to make living through the pandemic a little easier, with expert-backed answers to your toughest coronavirus-related dilemmas. While we can’t and don’t offer medical advice—those questions should go to your doctor—we hope this column will help you sort through this stressful and confusing time. Got a question? Write to us at [email protected]

Today, W.S. in Florida asks:

The second dose of Pfizer-BioNTech’s vaccine should ideally be given three weeks after the first. (Moderna’s second dose is meant to be given four weeks after the first, while the Johnson & Johnson/Janssen shot is delivered in a single dose.) But, well, sometimes life gets in the way. So what happens if you don’t make it to that second appointment?

Schedule another one as soon as you can, says Dr. Adam Ratner, a pediatric infectious disease doctor at NYU Langone Health and a vaccine researcher.

While a three- or four-week gap between shots is ideal, the U.S. Centers for Disease Control and Prevention (CDC) says you can get your second shot within 42 days of the first one and still mount a full immune response. “Beyond that, we start to operate in an area where there’s simply less data,” Ratner says.

That doesn’t mean your second shot will be ineffective if it’s given more than six weeks after the first. It only means that studies have not specifically measured how much protection the two-dose vaccines offer when the shots are given more than 42 days apart. Still, the CDC says you don’t have to start over if you can’t get a second vaccine within 42 days. Countries including the U.K. are even purposely delaying second shots so they can get first doses out to more people, and some experts in the U.S. advocate for the same policy.

Ratner says if he were in your shoes, he wouldn’t worry too much. “I would say get the second dose now and consider yourself fully vaccinated,” he says. Just make sure you get a second dose of the same vaccine, since the CDC does not recommend mixing and matching with different shots.

It may be tempting to just stick with the one dose you’ve got—after all, one recent study showed that a single dose of the vaccine was about 80% effective at preventing COVID-19 infections, compared to 90% protection after two doses. But “it is somewhat of a tenuous 80%,” National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci said at a recent press briefing. “When you leave it at one dose, the question is, ‘How long does it last?’”

To get the vaccine’s full benefits, and to make sure they last as long as possible, you’ll need a second shot.

Write to Jamie Ducharme at [email protected].

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