Five things to know about a possible fourth COVID-19 shot

Pfizer and Moderna have each asked the Food and Drug Administration (FDA) to authorize a second booster dose of their COVID-19 vaccines — essentially a fourth COVID-19 shot — for certain adults.

On Tuesday, Pfizer asked the FDA for emergency authorization for a second booster dose for people over the age of 65, while Moderna followed Thursday, asking for authorization for a second booster for all adults.

Pfizer CEO Albert Bourla said earlier this week that a fourth dose of the COVID-19 vaccine will be “necessary,” though the push for another vaccine dose has reignited debate over booster shots.

Appearing on CBS’s “Face the Nation” on Sunday, Bourla said the protection given by the third dose was “good enough” to protect against hospitalizations and death, but not quite as good for infections.

Here are five things to know about a possible fourth dose:

1. Pfizer’s is for those 65 and older, Moderna’s is for all adults

Pfizer asked the FDA for emergency use authorization to administer a second booster of its two-shot vaccine to those over the age of 65.

The company said a pair of real-world data sets indicated a fourth dose lowered rates of infection and severe illness, including one study of adults in Israel that measured antibodies in the blood.

Moderna’s request to the FDA applies to all adults who have received an initial two-shot immunization and a booster, not just the elderly.

Gigi Gronvall, senior scholar at the Johns Hopkins Center for Health Security, said it was a “good idea” for people in high-risk groups like the elderly and immunocompromised to get a fourth dose.

Gronvall added there could possibly be “diminishing returns” for administering a fourth dose to people outside of these high-risk groups.

2. The White House can’t afford boosters for everyone

On Tuesday, the White House said that if another booster shot is needed, it would not be able to fund enough doses for everyone due to continued pandemic funding being stalled in Congress.

“The federal government does not have adequate resources to purchase enough booster vaccine doses for all Americans, if additional doses are needed. The shortages will be even more acute if we need a variant-specific booster vaccine, since we will not have any existing supply,” the White House said in a fact sheet.

Officials have warned the lack of funding also threatens to impact testing capabilities and antiviral treatments for COVID-19. The administration has so far not offered a path forward for funding, saying it would “defer to Congress” when it comes to the specifics.

“As we enter a new moment in the pandemic, Congress has not provided us with the funding we need to continue the COVID-19 response and minimize the pandemic’s impact to the Nation and our economy,” the White House fact sheet stated.

3. Several countries are already administering fourth doses

Countries like Israel, Denmark and Chile have already been administering fourth COVID-19 doses to vulnerable groups.

Though only a few countries have taken part in offering a second booster to their citizens, these rollouts have given researchers the opportunity to study the effects and potential benefits of another shot.

When Pfizer announced its request for a second booster dose, it referenced an Israeli study of 700 adults that received a fourth dose that found antibodies in the blood increased seven- to eightfold at least three to four weeks after receiving a second booster shot.

One to two weeks after the additional booster was administered, researchers found a respective eightfold and tenfold increase in antibodies protective against the omicron variant, according to the company. Pfizer said the same study found no new safety concerns for people who were given a second booster dose.

A small pre-print study published last month from Israel found that a fourth COVID-19 jab only offered a small bump in protection from the first three doses, possibly only restoring the level of immunity that was lost from waning over time.

Gili Regev-Yochay, co-author of the study and an infectious diseases researcher at Sheba Medical Center in Israel, said young people may not reap that many benefits from a fourth dose, though it could still help the immunocompromised and elderly.

4. Many people haven’t gotten boosted at all

According to the Centers for Disease Control and Prevention, 44 percent of fully vaccinated people in the U.S. have received a booster dose, with 2 out of 3 people over the age of 65 getting a third dose.

About half the U.S. population that is eligible to receive a booster has yet to get one, accounting for nearly 89 million people.

According to public health experts, convincing people to get a fourth dose, if it is authorized, will likely mirror what happened when a third dose was authorized last year. People who were already open to getting a third dose will more than likely be open to a fourth dose.

“I don’t think that’s a heavy lift. I mean, people who have chosen not to get vaccinated already are probably not going to get vaccinated now,” said Philip Landrigan, public health physician and epidemiologist at Boston College.

“But people who’ve already been conscientious about being vaccinated, have acted to protect themselves and the people around them, I think will probably say, ‘I’ve already gotten three doses. I want to protect myself. I want to protect my family, I want to protect the people I go to school with, the people I [go to] church with.’”

“I think people that care about their neighbors will do what has to be done,” he added. 

5. Some health experts are still on the fence about a fourth shot

“There are just a lot of unknown unknowns here,” said Landrigan.

The epidemiologist said it was fair to be “cautiously optimistic” that three doses would suffice for the time being but said a fourth dose will likely be necessary.

Jesse Goodman, director of Georgetown University’s Center on Medical Product Access, Safety and Stewardship and an attending physician on infectious diseases, said he was still not convinced.

“I’m not yet convinced that the time is right now to go with a fourth dose. But if that waning protection against severe infection is clearly documented, and then if we see that a fourth dose can overcome that for more than just days to weeks, that would be something to consider,” Goodman said during a press briefing.

However, former FDA official Henry Miller said he was “bullish” to the idea of another booster dose.

“I would love to see the summary that Pfizer presents to FDA,” said Miller. “But I don’t anticipate anything surprising. I mean we’ve been through this now with three doses. That is an extremely safe and very effective vaccine.”