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A Fourth Vaccine Dose May Not Boost Protection Against Omicron, Early Data Shows

Blue gloved hands holding a syringe and filling it from an ampule of vaccine.

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Key Takeaways

  • Early results from clinical trials in Israel that have put COVID-19 vaccine boosters up against the Omicron variant have not been reassuring.
  • While participants in the trial saw an increase in COVID-19 antibodies, the booster may not help prevent people from catching the Omicron variant.
  • Second boosters are being administered in Israel, but they are not yet offered in other parts of the world.

According to preliminary results of two clinical trials in Israel, a second booster dose of a Pfizer or Moderna COVID-19 vaccine does not look promising against breakthrough infections caused by the Omicron variant.

The early unpublished findings were presented by Gili Regev-Yochay, MD, MSc, MPH, chief of infectious diseases at Sheba Medical Center in Tel Aviv, Israel, and the leader of the research, at a briefing for reporters on January 17.

Testing Boosters

According to Regev-Yochay, the trials were designed to “check the efficacy of the vaccines and compare the results of antibody levels and defense against Omicron.”

The trials included 274 people who worked at Sheba Medical Center in Tel Aviv. All the participants had previously received a total of 3 doses of the Pfizer COVID vaccine. In the trial, 154 people got an additional Pfizer dose as a booster and the other 120 got a booster of Moderna’s COVID vaccine.

According to Regev-Yochay, “the rise in antibody levels that we saw with both Moderna and Pfizer are slightly higher than what we saw after the third vaccine.”

However, because more people are getting Omicron (even with those increased antibodies), “the fourth vaccine only offers a partial defense against the virus.”

Regev-Yochay concluded that while the vaccines were effective against previous variants, they “offer less protection versus Omicron.”

Even still, Regev-Yochay also acknowledged during the briefing that it’s likely a good idea to administer boosters to people who are high-risk.

Doling Out Fourth Doses

The Israeli government isn’t waiting for the clinical trials to end before taking action—the country has already started giving some citizens a fourth vaccine dose.

The Israeli Health Ministry recently authorized fourth doses for Israelis aged 60 and older, people who are immunocompromised, and healthcare workers. According to the Times of Israel, as of January 16, over 500,000 Israelis had received a fourth vaccine.

Still, COVID cases in Israel continue to rise. Reuters reported on January 18 that the 7-day average for new COVID cases in Israel is 3,290 infections per 100,000 people—the highest level since the pandemic began. And it’s still going up.

Additional Dose vs. Booster

COVID vaccine boosters are given to people who have completed their initial series of doses and just need to “boost” their immunity, which will naturally wane over time.

An additional dose of a vaccine is given to people who might not have mounted a good response to the first dose—for example, someone with a compromised immune system.

Who Needs Second Boosters?

While disappointing, the Sheba Medical Center trial data will inform the conversation around whether Americans will need a second booster.

In the U.S., Anthony Fauci, MD, has repeatedly said that the government will be looking closely at the Israeli data on second boosters. As of January 18, Fauci had yet to comment on the latest findings from the Israeli trial.

Who's Getting 4 Doses In the U.S.?

Currently, the Centers for Disease Control and Prevention (CDC) recommends that people who are immunocompromised receive three primary doses of a Pfizer or Moderna vaccine, plus a booster dose at least five months after the last dose of their primary series.

For immunocompromised people who got the one-dose Johnson & Johnson vaccine, the current CDC guidance is to get a booster dose—preferably of either the Pfizer or Moderna vaccines rather than a second J&J shot—at least two months after their first shot.

“There are some basic flaws that people have in their understanding of how the vaccines work,” Aaron Glatt, MD, chief of infectious diseases at Mount Sinai South Nassau, told Verywell. “Antibody levels are the wrong way to assess whether a vaccine is effective or not. The only real way is to assess clinical severity of illness."

Glatt said that at this point, they would only suggest a fourth dose if someone could demonstrate that “there was more severe clinical disease in patients with only three doses versus those that received an additional fourth dose. As there is no evidence of such at this time, I do not routinely recommend that people get a fourth dose.”

According to a National Institutes of Health (NIH) spokesperson, the NIH is funding a second booster shot clinical trial in the U.S. The trial is currently enrolling kidney and liver transplant recipients who got two to four doses of a COVID-19 mRNA vaccine and did not produce an antibody response.

The study will look at whether an additional booster dose on its own or paired with a reduction in immunosuppressive medication, could increase COVID antibodies in these patients.

Will We Ever Have a Vaccine Against Omicron?

What will be effective against the Omicron variant? Regev-Yochay told Verywell that an Omicron-specific vaccine might be needed.

On January 18, Stat News reported that if the Food and Drug Administration (FDA) decides to update COVID vaccines to be more effective against variants, it will likely coordinate with international partners, as it does for the annual influenza vaccine.

What This Means For You

Early data from clinical trials in Israel suggests that getting a fourth dose of the COVID vaccines may not be enough to keep you from getting Omicron. However, getting your initial vaccine series is still crucial to protecting yourself and others.

That said, people who are at high-risk (such as those with compromised immune systems) might be able to get a fourth COVID vaccine dose.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  1. Centers for Disease Control and Prevention. Interim clinical considerations for use of COVID-19 vaccines currently approved or authorized in the United States.