Here’s Why You’ll Need a Third Dose of the COVID-19 Vaccine

An expert explains the science behind the decision
booster shot, third shot, COVID-19, pandemic, coronavirus, vaccines

With the delta variant driving a new surge of cases, including a rising number of breakthrough cases for fully vaccinated people, attention has turned to the need for another COVID-19 vaccine dose.

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New data suggests that while the current vaccines have so far proven effective against COVID-19, the protection they offer may fade after a while.

Using that data, the U.S. Department of Health and Human Services (HHS), the CDC, the FDA and other experts in the medical field and federal government announced plans earlier in the summer of 2021 to distribute a third dose of the COVID-19 vaccine this fall. In a joint statement, the group said, “We conclude that a booster shot will be needed to maximize vaccine-induced protection and prolong its durability.”

By October 2021, the FDA expanded the list of those eligible for an additional dose of any of the three COVID-19 vaccines. To better understand what data experts are seeing and why it points to a need for a third dose of the vaccine, we talked to digestive disease expert and Lerner Research Institute Chair, Thaddeus Stappenbeck, MD, PhD.

Why do I need a third dose?

New research indicates that the protection the two mRNA vaccines – Pfizer and Moderna – create against COVID-19 might fade after several months. The data comes from a study of vaccinated patients in Israel, where the Pfizer vaccine was the predominant option and vaccinations began in December 2020, ahead of many other countries, including the United States.

According to the study, as the delta variant spread through Israel in the early summer of 2021, there was a correlation between receiving the vaccine at an earlier date and contracting a breakthrough case. For example, patients vaccinated in January 2021 were 2.26 times more likely to contract a breakthrough infection than those vaccinated in April 2021.

“The trials for the mRNA vaccines showed us they were up to 94% effective in protecting patients from infection,” says Dr. Stappenbeck. “But because of the situation, the other main point of those trials was to establish safety so we could start vaccinating people. We’re still learning how long that protection lasts and based on what we’ve seen in Israel, it starts to fade around six months for some people.”

He adds that the data hasn’t been investigated deeply enough yet to see if there’s evidence of why the immunity level of some people may drop. “What’s clear, though, is that more people are being exposed to the delta variant, and more people that are vaccinated are getting breakthrough infections than the initial data suggested,” he says.

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How do I know if my immunity is fading?

The unfortunate thing is that there’s no easy way to measure if your immunity to COVID-19 is fading, particularly if you’re a healthy adult, says Dr. Stappenbeck. “Immunity is a multi-factor thing that’s not just about the number of antibodies to a specific virus that you have in your bloodstream,” he notes. “There’s a cellular-based immunity, too, and that’s harder to measure.”

The biggest challenge for experts is that COVID-19 is a new virus — one that continues to evolve, mutate and force doctors and researchers to adapt on the fly. “It’s a moving target,” Dr. Stappenbeck says. “New data is coming out every day and we have to really watch this over the next several weeks and months.”

It’s important to note that the Pfizer and Moderna vaccines are incredibly effective against the delta variant. But a third dose would further strengthen immunity against the virus and Pfizer shared data with the FDA on this point, saying, “The data we’ve seen to date suggests a third dose of the vaccine elicits antibody levels that significantly exceed those seen after the two-dose primary schedule.”

What about the Johnson & Johnson vaccine?

In their update to the booster parameters in October 2021, the FDA said recipients of the Johnson & Johnson vaccine, ages 18 and up, are eligible to receive a booster of any of the three available vaccines.

Who is eligible for the third dose?

The FDA and CDC originally approved third doses for certain immunocompromised patients. These patients include:

  • Patients receiving active cancer treatments.
  • Organ transplant patients.
  • Recent stem cell transplant patients.
  • Patients with advanced or untreated HIV infection.
  • Patients with moderate or severe immunodeficiency.
  • Patients being treated with medication that suppresses the immune system.

As of October 20, 2021, the FDA has also cleared booster shots for all three COVID-19 vaccines for certain recipients in the United States. For those who received the Pfizer and Moderna vaccines for their initial doses, an additional dose is recommended for:

  • Patients age 65 and up.
  • Patients age 18 and up who are considered high-risk for a severe case of COVID-19.
  • Patients age 18 through 64 who may be frequently exposed to COVID-19 due to their work.

As mentioned above, anyone age 18 and up who received the Johnson & Johnson vaccine as their initial dose is eligible for a booster, too.

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When can I get my third dose?

As of right now, says Dr. Stappenbeck, points to the expert statement which outlines a rollout similar to what we saw with the original doses — with priority going to older, at-risk patients and healthcare workers beginning in late September.

“We’re watching this develop and waiting for those guidelines but, if you’re healthy and vaccinated, I wouldn’t panic about getting a third dose right now,” he adds.

What should I do while I wait for my third dose?

The best thing to do, says Dr. Stappenbeck, is to continue practicing social distancing guidelines, including wearing masks, six-foot distancing and maintaining good hand hygiene. This is especially true if it’s been more than six months since you’ve become fully vaccinated.

“Again, that doesn’t mean your protection has weakened since it varies from person to person,” he says. “We know that protection lasts at least six months, maybe longer. These are very unique circumstances and we’re still learning everything we can.”

In the meantime, he says, continue to be safe, and if you’re not already, get vaccinated now. “All of the real-world data suggests the vaccines are effective against the delta variant and it’s the best protection you have.”

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