The CDC Says Don't Wait Longer Than This to Get Your Second COVID Shot

Waiting beyond this timeframe can make the vaccines less effective.

As the nation rapidly expands eligibility for the COVID vaccine, you may soon find yourself in a position to get the shot if you haven't already. And if you're planning on getting the Moderna of Pfizer vaccine, scheduling will be of the utmost importance. Not only should you consider whether you're free the day of your first jab, but you should also take into account whether you foresee any difficulty showing up for the second dose three to four weeks later. As experts at the Centers for Disease Control and Prevention (CDC) point out, there are limitations to how long you can wait between your first and second appointments before risking rendering the vaccine less effective. For this reason, the CDC advises getting the second dose no later than six weeks after the first. Read on for more on the CDC's recommendation, and for more essential vaccine news, This Is Why Half of People Have Stronger Vaccine Side Effects, CDC Says.

According to the CDC, most people have been diligent in attending both vaccine appointments on time. "A review of recent vaccine administration data across all jurisdictions shows that, as of January 30, 2021, of those persons completing their second dose series, 96 percent received their second dose on or within four days of the recommended 3-4-week time interval," they explain.

However, in some rare instances, second appointments have been delayed. In those cases where the recommended interval cannot be achieved, the health authority grants a total of 42 days from the initial appointment to complete the second dose. After that, second doses will "not be held or saved for patients who have not returned after 42 days following their first dose," a CDC policy states.

So, what happens if you skip your second dose entirely? It depends on which vaccine you receive. Clinical trial data shows the Pfizer vaccine is only about 52 percent effective after the first dose, but 95 percent effective after the second. Meanwhile, the BBC reports that the Moderna vaccine is about 80 percent effective after a single dose. After the second dose, it's 95 percent effective in people ages 18 to 65 and almost 87 percent effective in those over 65. In either case, you're taking your chances with a less-than-maximally-effective vaccination if you miss your second shot.

Of course, if you suspect you'll have trouble making time for a second vaccine appointment, you can always opt for the Johnson & Johnson jab, which requires only one shot to be fully effective. Read on for more tips on making your two-dose vaccination plan, and for more essential vaccine news, The Pfizer CEO Just Said Which Other COVID Vaccine He Recommends.

Your second dose may come with more side effects.

A young woman lies on the couch while covered by a blanket and a tired expression on her face

Certain side effects are more common following the second vaccine dose because the immune system already recognizes the supposed "threat" from the first time around, according to experts.

"When the body's immune system sees [the vaccine] a second time, there are more cells and there's a more intense immune response, resulting in those side effects," Bill Moss, MD, a pediatrician and professor of infectious disease epidemiology at the Johns Hopkins Bloomberg School of Public Health recently told Today. And for the latest health news delivered straight to your inbox, sign up for our daily newsletter.

Or you may have no side effects at all.

gray haired woman getting a covid vaccine from young female doctor
Shutterstock/Yuganov Konstantin

While you may be bracing yourself for side effects after your COVID vaccine, doctors say you may not experience any—and that shouldn't make you worry about the vaccine's efficacy. Even though vaccine side effects are physical evidence that the immune system is kicking into high gear, a lack of side effects shouldn't be taken as cause for concern.

The CDC's official vaccine guidance says that this is considered perfectly normal, noting that "some people have no side effects." And for more on COVID vaccine side effects, This COVID Vaccine Has the Lowest Rate of Side Effects, Data Shows.

You may only need one dose if you've already had COVID.

woman getting vaccine from doctor in face shield and scrubs
Shutterstock/Sabrina Bracher

Besides getting the one-dose Johnson & Johnson vaccine, there's one other instance where receiving just one dose is considered acceptable. Researchers say that you can talk with your doctor about receiving a single dose of either the Pfizer or Moderna vaccine if you've already had COVID.

One study, which analyzed blood samples of those who had received the vaccine after recovering from COVID, found that one dose amplified the number of antibodies in patients' blood by a thousandfold. The study's lead author Andrew T. McGuire, PhD, called this "a massive, massive boost" in an interview with The New York Times.  The article further explains that "the antibodies seemed to perform better than those in people who had not had COVID and had received two doses of a vaccine."

You shouldn't get the second shot earlier than recommended.

Calendar circled for COVID vaccine

If you can't make it to your appointment to get the second shot of your COVID vaccine exactly 21 days after your first Pfizer dose or 28 days after your first Moderna dose, the CDC says you should schedule it shortly thereafter.

However, if you absolutely must schedule it sooner, they shared this recommendation: "Second doses administered within a grace period of 4 days earlier than the recommended date for the second dose are still considered valid." And if you're ready to get your shot, Don't Do This the Night Before Your Vaccine Appointment, Experts Say.

Lauren Gray
Lauren Gray is a New York-based writer, editor, and consultant. Read more
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