Experts split on boosting the boosters

The drug companies behind two of the most widely used COVID-19 vaccines in the United States are seeking emergency use authorization for a second booster dose of their formulations, but scientists and doctors are divided over its value.

The US Food and Drug Administration announced on Monday that an advisory panel will meet on April 6 to discuss the booster doses. The drugmakers seeking the go-ahead are Pfizer and BioNTech, which teamed up for their vaccine, and Moderna.

The agency said the discussion next month will focus on factors such as whether the vaccines need to be updated to address new coronavirus variants, as well as the timing and target groups for booster doses.

Pfizer and BioNTech asked the FDA on March 15 to authorize a second booster shot for people aged 65 and older, while Moderna asked the agency on March 17 to authorize a second booster for all adults.

The moves come amid signs that the US could experience another COVID-19 surge as the Omicron subvariant known as BA.2 accounts for around a quarter of all new sequenced cases in the US, and that proportion appears to be increasing, according to the Centers for Disease Control and Prevention.

The variant is also spreading throughout Europe and other parts of the world.

The FDA panel, along with the CDC, is widely expected to approve Pfizer's request－a fourth shot for older people－because they make up the group most likely to be hospitalized or die of COVID-19, political news site The Hill reported.

A CDC study released last month found that the effectiveness of the Pfizer-BioNTech and Moderna vaccines against hospitalization decreased from 91 percent two months after the initial booster shot to 78 percent after four months.

Another study, according to Pfizer in a news release, found that rates of severe illness were four times lower among individuals who received a second booster, compared with those who received only one booster shot.

"We know that the duration of the protection doesn't last very long," Pfizer chief executive Albert Bourla said in an interview with CBS' Face the Nation on Sunday. "It is necessary, a fourth booster right now."

Henry Miller, a former FDA official, said he was "bullish" on the idea of another booster dose. "I don't anticipate anything surprising. I mean we've been through this now with three doses. That (the Pfizer-BioNTech vaccine) is an extremely safe and very effective vaccine," he said.

But Cornell University virologist John Moore said: "Pfizer seems to be saying that, because their vaccine isn't very good, people need more of it. If the FDA approves another dose, it would make sense to use a stronger vaccine instead, like Moderna or eventually Novavax."

Efficacy questioned

Many health experts have questioned how well COVID-19 vaccines have prevented serious disease in younger healthy people, and whether and how often they should be boosted.

"To be sure, the evidence that drugmakers have shared isn't all that compelling to some scientists," Jesse Goodman of Georgetown University, a former FDA vaccine chief, was quoted by NBC News as saying during a news conference.

"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."

Countries such as Israel, Denmark and Chile have been administering fourth doses to vulnerable groups.

A study published on March 16 in The New England Journal of Medicine found that a fourth dose did not differ significantly in levels of protective antibodies against the Omicron variant compared with the third dose. The study from Israel surveyed more than 800 healthy young healthcare workers.

A small preprint study published last month from Israel also found that a fourth dose provided only a small increase in protection from the first three doses, possibly only restoring the level of immunity that was lost from the waning over time.