Covid 19 Omicron outbreak: FDA okays another Pfizer, Moderna Covid booster for 50s and up

US regulators authorised another Covid-19 booster for people aged 50 and older, a step to offer extra protection for the most vulnerable in case the coronavirus rebounds.

The Food and Drug Administration's decision opens a fourth dose of the Pfizer or Moderna vaccines to that age group at least four months after their previous booster.

Until now, the FDA had cleared fourth doses only for people 12 and older who have severely weakened immune systems. The agency said this especially fragile group also can get an additional booster, a fifth shot.

The latest expansion, regardless of people's health, allows an extra shot to millions more Americans — once the Centres for Disease Control and Prevention makes its own recommendations. One lingering question is whether everyone who is eligible should seek the dose right away.

Everyone eligible for a first booster who hasn't gotten one yet needs to, FDA vaccine chief Dr Peter Marks said. But the second booster is only for higher-risk groups because there's evidence protection can wane and FDA decided the option "will help save lives and prevent severe outcomes".

The Food and Drug Administration has authorised another booster dose of the Pfizer or Moderna COVID-19 vaccine for people age 50 and up. Photo / AP

The move comes at a time of great uncertainty. Covid-19 cases have dropped to low levels after the northern winter surge of the super-contagious omicron variant. Two vaccine doses plus a booster still provide strong protection against severe disease and death, CDC data show.

But an omicron sibling is causing a worrisome jump in infections in Europe - and spreading in the US — even as vaccination has stalled. About two-thirds of Americans are fully vaccinated, and half of those eligible for a first booster have not had one.

Pfizer had asked the FDA to clear the fourth shot for people 65 and older, while Moderna requested another dose for all adults "to provide flexibility" for the government to decide who really needs one.

FDA's Marks said regulators set the age at 50 because that's when chronic conditions such as heart disease and diabetes become more common, increasing the risks from Covid-19.

Marks said immune-compromised patients are more likely to see their immune protection wane sooner so can benefit more from extra protection. Only the Pfizer vaccine can be used in those as young as 12; Moderna's is for adults.

There's limited evidence to tell how much benefit another booster could offer right now.

FDA made the decision without input from its independent panel of experts that has wrestled with how much data is required to expand shots.

"There might be a reason to top off the tanks a little bit" for older people and those with other health conditions said University of Pennsylvania immunologist E. John Wherry, who wasn't involved in the government's decision.

But while he encourages older friends and relatives to follow the advice, Wherry, 50 — who is healthy, vaccinated and boosted — doesn't plan on getting a fourth shot right away. With protection against severe illness still strong, "I'm going to wait until it seems like there's a need".

None of the Covid-19 vaccines are as strong against the Omicron mutant as they were against earlier versions of the virus. Also, protection against milder infections naturally wanes over time. But the immune system builds multiple layers of defence and the type that prevents severe illness and death is holding up.

During the US Omicron wave, two doses were nearly 80 per cent effective against needing a ventilator or death — and a booster pushed that protection to 94 per cent, the CDC recently reported. Vaccine effectiveness was lowest — 74 per cent — in immune-compromised people, most of whom hadn't gotten the third dose.

US health officials also looked to Israel, which during the Omicron surge opened a fourth dose to people 60 and older at least four months after their last shot. The FDA said no new safety concerns emerged in a review of 700,000 fourth doses administered.

Preliminary data posted online last week suggested some benefits: Israeli researchers counted 92 deaths among more than 328,000 people who got the extra shot, compared to 232 deaths among 234,000 people who skipped the fourth dose.

What's far from clear is how long any extra benefit from another booster would last, and thus when to get it.

"The 'when' is a really difficult part. Ideally, we would time booster doses right before surges but we don't always know when that's going to be," said Dr William Moss, a vaccine expert at the Johns Hopkins Bloomberg School of Public Health.

Plus, a longer interval between shots helps the immune system mount a stronger, more cross-reactive defence.

"If you get a booster too close together, it's not doing any harm — you're just not going to get much benefit from it," said Wherry.

The newest booster expansion may not be the last: Next week, the Government will hold a public meeting to debate if everyone eventually needs a fourth dose, possibly in the northern autumn, of the original vaccine or an updated shot.

Even if higher-risk Americans get boosted now, Marks said they may need yet another dose in autumn if regulators decide to tweak the vaccine.

For that effort, studies in people — of Omicron-targeted shots alone or in combination with the original vaccine — are under way. The National Institutes of Health recently tested monkeys and found "no significant advantage" to using a booster that targets just Omicron.