For a long time now, the US Food and Drug Administration (FDA) has been signaling that this Fall might see a fourth rollout of COVID-19 vaccine shots. But now, with the Omicron BA.5 subvariant outnumbering pretty much any other virus out there, those plans might be about to change.

Instead of offering a second round of booster shots, the Biden administration is hoping to accelerate the rollout of reformulated vaccines, specialized to fight the Omicron variants, federal health officials told the Washington Post this week. 

The news is in line with updated vaccine recommendations from the World Health Organization (WHO), who earlier this year cautioned that “a vaccination strategy based on repeated booster doses of the original vaccine composition is unlikely to be appropriate or sustainable.” 

The FDA followed suit in late June, directing companies like Moderna and Pfizer to develop a two-part vaccine that can target the newer variants of concern as well as the original virus. The federal government has already agreed to purchase 105 million doses of Pfizer-BioNTech’s rebooted vaccine, and a similar contract with Moderna is expected to be signed in the near future.

If all goes to plan, the redesigned vaccines could be available as early as September. A final decision on the policy switch has not yet been announced – though one is expected, potentially by the end of the week.

The problem facing health authorities is one of immunity, and how to optimize the effectiveness of future Omicron vaccines. The US is currently facing what may be its second-largest wave of COVID infections, and is “headed in a bad direction,” according to Jason Salemi, an associate professor of epidemiology at the University of South Florida’s College of Public Health. 

“We’ve seen it coming for a while… We’ve seen it go pretty unabated,” he told The Guardian earlier this month. “There’s a lot of opportunity for waning immunity and waning protection from the vaccine to allow these new circulating variants to do a little bit more damage.”

The best way to counteract waning immunity is to get a booster shot – but some experts warn that taking a reformulated booster too soon after a classic version could backfire.

“If you get a booster now with the original formulation of the vaccine, this may in fact be counter-productive,” Dr Céline Gounder, an internist, infectious disease specialist, epidemiologist, and senior fellow at the Kaiser Family Foundation, told NPR. “It may prevent the second booster dose given this fall from taking and from you developing an immune response to that booster.”

Others, though, don’t think it’s worth the risk. There’s no guarantee the Omicron-specific shots would be ready by September, they say – and even if they were, who says the BA.4 and BA.5 subvariants that the new boosters are being designed for will still be dominant? 

So holding off on a second round of vaccine boosters could mean “literally hundreds of millions of people ... are at a higher risk than they need to be for months,” Dr Robert Wachter, chair of the department of medicine at the University of California, San Francisco, told NPR. 

“And that will mean potentially millions of preventable infections, certainly thousands of preventable hospitalizations, and probably hundreds of preventable deaths,” he said.

In the end, though, it may come down to more practical concerns. Federal bodies currently have vaccines that are nearing their expiration, and so-called “booster fatigue” has long since set in. Barely more than one in four adults over 50 have received a second booster shot, and some experts have suggested that offering two more so close together may erode trust in the government’s COVID strategy.

But one thing’s for sure: either booster is better than none. 

“There’s a lot of handwringing around what the composition of the booster should be,” Dr William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, told Healthline. “But the real determining factor will be how many people will actually get that additional booster dose.”