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

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The early unpublished findings were presented by Gili Regev-Yochay, MD, MSc, MPH, chief of infectious diseases at Sheba Medical Center in Tel Aviv, Israel, and the leader of the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.

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.

“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.

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.