Most Americans Should Get the New COVID-19 Booster Shot to Be Fully Vaccinated. Here’s How to Know if You’re Eligible

Most likely, you felt pretty triumphant scoring your first shot of the COVID-19 vaccine. After all, it was a huge step forward.

But more than a year may have passed since you received that initial jab in your arm. Those first deliveries of vaccines began back in December 2020, according to the U.S. Department of Health & Human Services (HHS). And if you didn't complete your primary series of Pfizer or Moderna shots, along with getting boosted, you're not "fully vaccinated."

Research suggests that the effectiveness of the vaccine decreases over time, according to the Centers for Disease Control and Prevention (CDC). Luckily, getting a booster shot can provide continued protection from the virus (and its variants).

In November 2021, all adults over age 18 became eligible for a booster shot, per the HHS. As of September 2022, an updated (bivalent) booster became available. The bivalent booster shot protects against both the original virus that causes COVID-19 as well as two more recent Omicron variants, per the CDC.

The bivalent booster was initially only available for adults and kids older than 12, but in October 2022, the CDC expanded use to include children ages 5 to 11.

If it's been at least two months since your last COVID-19 vaccine (either the primary 2-dose series or the earlier monovalent booster), and you're over age 5, you should receive an updated bivalent booster, per the CDC.

Bottom line: Most people should aim to get this bivalent booster.

There are some subtleties to booster recommendations based on your age, timing of your last dose dose, whether you're immunocompromised and which shots you've previously received. Here are more detailed recommendations from the CDC:

• ‌Adults ages 18 and older:‌ After completing the two-shot series for Pfizer or Moderna, you can have the bivalent booster shot two months after your second primary dose (or, two months after your last booster, if you received one). If you had the single-shot Johnson & Johnson/Janssen vaccine, you're eligible for the bivalent booster two months after that initial vaccine or two months after your most recent booster. Note: The original (monovalent) booster shots from Pfizer and Moderna are no longer available.
• ‌Children, teens and adults who are moderately or severely immunocompromised:‌ For this group, the primary vaccine series is three doses — not two. You're eligible for a fourth dose (the bivalent booster) two months after your third dose or last booster.
• ‌Children and teens:‌ Children ages five and up who completed the initial two-shot primary series for Pfizer are eligible for the bivalent Pfizer booster two months after getting their last booster shot or completing the primary series, per the FDA. The bivalent Moderna vaccine can be given to children as young as age 6 — again, children need to be at least two months out from their last booster shot or from completing the initial primary series.
• ‌Children who are immunocompromised:‌ Children who are 5- to 11-year-old and immunocompromised are eligible for the bivalent Pfizer booster two months after completing their three-dose primary schedule. A booster is not recommended for children between the ages of 6 months and 4 years who have completed the initial Pfizer series. Five-year-olds who completed the Moderna series are eligible for the Pfizer booster. Children ages 6 to 11 who completed the Moderna series can opt for either booster.

With some exceptions, mixing and matching the brand of boosters is permitted. In other words, you can, for example, get a Pfizer booster shot even if you initially received a primary series of Moderna vaccines.

Having COVID-19 gives you some short-term immunity — but won't stop you from getting the virus again.

That said, if you recently had COVID-19, consider delaying your next shot to three months after you initially experienced symptoms or tested positive, per the CDC. Depending on your individual risk factors and how prevalent the virus is in your community, you may opt to get the booster sooner.

Rather than "fully vaccinated," the CDC uses the wording "up to date."

You're considered up to date on your COVID-19 vaccines "if you have completed a COVID-19 vaccine primary series and received the most recent booster dose recommended for you by the CDC," per the CDC.

But, keep in mind the protection of COVID-19 vaccines is not immediate — typically, it takes a few weeks, per the CDC.

So, for instance, if you're still getting your primary doses (whether that's a recommended 2-dose or 3-dose series), you're not fully protected until some time has passed after the series.

"We want to make sure that, with the mRNA vaccines, you are two doses in plus 14 days. That is the point in time where you can feel vaccinated," Keri Althoff, PhD, MPH, associate professor in the department of epidemiology at the Johns Hopkins School of Public Health said during a media briefing about how vaccines might shape daily life.

That's the amount of time needed for your body to appropriately respond to the vaccine, Althoff said. During this period, your immune system is in the process of producing antibodies so your body can learn and remember how to protect itself against COVID-19 infection.

Protection takes time with the bivalent booster shots, too. While antibodies are produced days after the booster shot, most likely, full protection takes about two weeks, according to the Johns Hopkins Bloomberg School of Public Health.

Before you can get a bivalent booster, you need to complete your primary vaccine series of Pfizer or Moderna (or a single shot of the Johnson & Johnson/Janssen vaccine).

Since both the Pfizer and Moderna vaccines have multiple doses, you may wonder how much protection you actually have after your first dose — and before your second (or third, as needed) dose.

The fortunate news is that after your first dose, you do have a pretty good level of protection. In an April 2021 study from the CDC on nearly 4,000 health care workers, mRNA vaccines (Pfizer and Moderna) were 80 percent effective 14 days after the first dose, which is considered "partial immunization." At 14 days after the second dose, they were considered to be fully immunized and were 90 percent protected against infection in real-world settings. In clinical trials, the Johnson & Johnson vaccine was 66.3 percent effective in preventing illness, per the CDC.

Still, even with this 90 percent, the CDC stresses that you still need multiple doses to receive the full benefit of vaccination. Given that there are COVID variants circulating that are more easily spread from person-to-person, you want all the protection you can get.

Vaccines cannot guarantee you won't get sick. Breakthrough COVID-19 infections (that is, infections that happen even after being vaccinated) do occur. But for people who receive all shots, including recommended boosters, vaccines protect against severe illness, hospitalization and death, per an August 2022 CDC report on the effectiveness of vaccines.