Pfizer and Moderna experiment with modified doses against a mutant that emerged in South Africa
More COVID-19 booster shots may be on the way – but when it’s your turn, you’ll get an extra dose of the original Vaccination, not updated to better match the extra-infectious delta version.
And that has some experts wondering whether the booster campaign has missed an opportunity to target Delta and its potential descendants.
“Don’t we want to match new strains that are likely to be circulating as closely as possible?” Food and Drug Administration consultant Dr. Cody Meisner of Tufts Medical Center recently challenged scientists at Pfizer.
“I don’t understand why it’s not a delta because that’s what we’re facing right now,” fellow advisor Dr Patrick Moore from the University of Pittsburgh said last week. Government experts debate whether it is time for the Modern Booster. He wondered whether such a switch would be particularly useful for preventing mild infections.
Simple answer: The FDA last month added additional doses of Pfizer’s original prescription after studies showed it still worked well enough against Delta — and those supplements could be rolled out immediately. Now the FDA is weighing the evidence for boosters for the original Moderna and Johnson & Johnson vaccines.
“It’s less churn and burn on manufacturing” to switch formulas only when it’s really necessary, said FDA vaccine chief Dr. Peter Marks.
But Pfizer and Moderna are hedging their bets. They are already testing optimized experimental doses for Delta and another variant, learning how to rapidly change the formula when a change is needed – for today’s mutants or brand new. The tough question for regulators is how they will decide whether and when to order such switches.
What we know so far:
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Existing vaccines are also working against Delta
Even after the arrival of the delta version, the vaccines used in the US remain strongly effective against hospitalization and death from COVID-19, but officials expect less protection against less serious infections and higher-risk populations. have hope. Studies show that an additional dose of the original formulas increases virus-fighting antibodies that prevent infection, including antibodies that target Delta.
Could a Delta-specific booster work even better?
Vaccines target the spike proteins that coat the coronavirus. Richard Webby, a virus specialist at St Jude Children’s Research Hospital, said mutations in that protein made Delta more contagious, but to the immune system, it doesn’t look all that different.
That means there’s no guarantee the Delta-specific booster will protect any better, said immunologist John Varys of the University of Pennsylvania. Waiting for studies to settle that question — and, if necessary, create updated doses — will delay rolling out boosters to those who need them now.
Still, because Delta is now the dominant version of the virus worldwide, it will almost certainly have a common ancestor that evolved further in the mostly unrelated world, said Trevor Bedford, a biologist and genetics specialist at the Fred Hutchinson Cancer Research Center. .
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A delta-updated vaccine “would help provide a buffer against those additional mutations,” he said. Bedford is paid for by the Howard Hughes Medical Institute, which also supports the Associated Press Health and Science Department.
Pfizer and Moderna’s vaccines are made with a piece of genetic code called messenger RNA that tells the body to make harmless copies of the spike protein, so it is trained to recognize the virus. Updating the formula only required swapping the original genetic code for the mutated spike protein with that of the mRNA.
The two companies previously experimented with modified doses against a mutant that emerged in South Africa, the beta version, which has been the most vaccine-resistant ever, far more so than the delta version. Lab tests showed that the updated shots produced potent antibodies. But the beta version did not spread widely.
Now companies have studies going on in fully vaccinated people who have agreed to test booster doses to match Delta. Moderna’s studies also include some shots that combine protection against more than one version of the coronavirus — much like today’s flu vaccines work against multiple influenza strains.
mRNA vaccines are considered the easiest type to tweak, but some other vaccine manufacturers are also exploring how to change their recipes if necessary.
FDA staff doesn’t take position on modern COVID-19 boosters
Why study updated shots if they are not needed yet?
Moderna’s Dr. Jacqueline Miller told an FDA advisory panel last week that the company is studying a variety of specific boosters to see if they provide benefits, and be ready if needed.
And Pence Very said it is important to carefully analyze how the body reacts to the updated shots because the immune system “imprints” a strong memory of the first virus strain. This raises questions about whether a subtly different booster would induce a temporary jump in the body’s previously created antibodies – or a larger target, a broader and more sustainable response that would be better positioned to come up with the next mutation. Might be possible.
no rules yet to switch
“What is a tripping point?” Webby, which is part of the World Health Organization network that tracks the evolution of influenza. “A lot more needs to go into making that decision that, unfortunately, is being learned from experience.”
Bedford said now is the time to decide what decline in vaccine effectiveness will trigger a formula change, as is done with flu vaccines every year.
This is not important only if a dramatically worse form suddenly develops. Like many scientists, Bedford hopes the coronavirus will eventually turn from a global crisis into a routine threat every winter – which could mean more regular boosters, perhaps even in combination with a flu shot.
The time between shots also matters, Wherry said.
“Your boostability can actually improve with longer intervals between stimulations,” he said. While scientists have learned a lot about the coronavirus, “the story isn’t over yet and we don’t know what the final chapters say.”