Do I need a fourth COVID-19 shot? Probably not, experts say — but the jury’s still out.

• Israel is giving fourth COVID-19 shots to adults under 60 who have underlying health conditions.
• However, US experts seem to agree for now that three shots are enough.
• Boosters strongly protect against severe disease caused by Omicron and other variants of the coronavirus.

The rapid spread of Omicron has triggered a fresh wave of COVID-19 infections – including in people who’ve received three vaccine doses. As such, scientists, health officials, and Big Pharma CEOs have been debating whether or not fourth shots could further blunt the variant’s impact.

Dr. Anthony Fauci, President Joe Biden’s medical advisor, told ABC News Sunday it was “entirely conceivable” that we “may need to boost again” depending on the longevity of third-shot boosters. Stéphane Bancel, CEO of Moderna, said in early January that fourth doses would probably be necessary this Fall.

In countries such as the US, UK, Chile, Denmark, and Sweden, people with weakened immune systems can already get fourth doses. Hungarians can get a fourth shot after a doctor’s consultation, per Reuters.

On Thursday, amid record-high case numbers, Israel announced that people younger than 60 with underlying health conditions can get a fourth dose to shore up immunity against Omicron. Israel’s vaccine advisory committee wants to go even further, though: its recommendation Tuesday was that everyone older than 18 should be allowed a fourth dose.

Yet the current thinking from scientists – and even Big Pharma CEOs – is that fourth doses aren’t necessary for most people.

John Moore, professor of microbiology and immunology at the Weill Cornell Medical College, told Insider that the US shouldn’t automatically do what Israel is doing. “Data generated here should determine our policies for our population,” he said.

Four doses or three?

The central question is whether everyone needs a fourth dose – and from old vaccines that were designed to fight the earliest form of the coronavirus. Omicron has 32 mutations in the part of the virus that existing vaccines target.

Three shots are more than 88% effective against Omicron hospitalization, real-world data from the UK and US has shown. Protection probably lasts at least three months, the data suggests, although what happens beyond that isn’t clear.

There is scant data to suggest that four doses of existing vaccines provide enough benefit over and above three doses. 

Preliminary data from Israel, cited by the country’s vaccine advisory committee, found that compared with three doses, four doses were three times more effective against serious illness and doubled protection against infection. The data was from people older than 60, not younger age groups.

Meanwhile, a separate, small study from Israel found that people were still catching Omicron even after four doses.

Neither study has been published or scrutinized by other experts in a peer-review.

Bob Wachter, a professor and chair of the department of medicine at the University of California, San Francisco, said on Twitter Thursday that if he was offered a fourth shot today, he’d hold off. With the exception of severely immunocompromised people, he said the evidence right now was “too weak.”

Mike Ryan, head of the health emergencies program at the World Health Organization, told STAT on January 3 that there were an “awful lot of unknowns” about fourth doses.

He added: “It can’t purely be the decision of one manufacturer to say, ‘Well, this is what we’re going to make, and this is what you’re going to buy.’ If it’s purely left to be a commercial decision, I’m not so sure that decision will necessarily be the best one.”

What about Omicron-specific shots?

Vaccines designed specifically for Omicron, or those that target multiple variants with one shot, would provide alternative options to fourth doses using the same vaccine. Neither are available yet.

On Sunday, Albert Bourla, CEO of Pfizer, told Israel’s N12 News that his company was creating a vaccine to cover Omicron and other variants, and that he hoped for a once-a-year shot. Pfizer said Tuesday it was also trialling a fourth dose of its original COVID-19 shot.

On January 17, at the World Economic Forum, Moderna’s Bancel acknowledged that existing vaccines were “holding.” Moderna said Wednesday that it too was testing an Omicron-specific shot, and that early lab tests suggested existing booster protection lasted six months.

Wachter said that while it was possible an Omicron-targeted vaccine could work better than existing shots, the high effectiveness of three shots against severe infection was “a high bar to cross.”