WASHINGTON (AP) — The U.S. on Wednesday authorized its first update to COVID-19 vaccines, booster doses that target today’s most common omicron strain. Shots could begin within days.

The move by the Food and Drug Administration tweaks the recipe of shots made by Pfizer and rival Moderna that already have saved millions of lives. The hope is that the modified boosters will blunt yet another winter surge — and help tamp down the BA.5 omicron relative that continues to spread widely.

“These updated boosters present us with an opportunity to get ahead” of the next COVID-19 wave, said FDA Commissioner Dr. Robert Califf.

Until now, COVID-19 vaccines have targeted the original coronavirus strain, even as wildly different mutants emerged. The new U.S. boosters are combination, or “bivalent,” shots. They contain half that original vaccine recipe and half protection against the newest omicron versions, BA.4 and BA.5, that are considered the most contagious yet.

The combination aims to increase cross-protection against multiple variants.

“It really provides the broadest opportunity for protection,” Pfizer vaccine chief Annaliesa Anderson told The Associated Press.

The updated boosters are only for people who have already had their primary vaccinations, using the original vaccines. Doses made by Pfizer and its partner BioNTech are for anyone 12 and older while Moderna’s updated shots are for adults — if it has been at least two months since their last primary vaccination or their latest booster. They’re not to be used for initial vaccinations.

There’s one more step before a fall booster campaign begins: The Centers for Disease Control and Prevention must recommend who should get the additional shot. An influential CDC advisory panel will debate the evidence Thursday — including whether people at high risk from COVID-19 should go first.

The U.S. has purchased more than 170 million doses from the two companies. Pfizer said it could ship up to 15 million of those doses by the end of next week. Moderna didn’t immediately say how many doses are ready to ship but that some will be available “in the coming days.”

The big question is whether people weary of vaccinations will roll up their sleeves again. Just half of vaccinated Americans got the first recommended booster dose, and only a third of those 50 and older who were urged to get a second booster did so.

Here’s the rub: The original vaccines still offer strong protection against severe disease and death from COVID-19 for generally healthy people, especially if they got that important first booster dose. It’s not clear just how much more benefit an updated booster will bring — beyond a temporary jump in antibodies capable of fending off an omicron infection.

Still, “people have to realize this is a different kind of booster than was previously available. It will work better at protecting against omicron,” said virologist Andrew Pekosz of the Johns Hopkins Bloomberg School of Public Health.

Even people who had an earlier omicron version still can get reinfected so “you should definitely go for the booster even if you’ve been infected in the last year,” added Pekosz. He thinks “if we can get good buy-in to use this, we might really be able to make a dent” in COVID-19 cases.

The FDA cleared the modifications ahead of studies in people, a step toward eventually handling COVID-19 vaccine updates more like yearly changes to flu shots.

FDA vaccine chief Dr. Peter Marks stressed the agency considered “the totality” of evidence. Pfizer and Moderna have previously brewed vaccine doses updated to match earlier mutants — including the omicron strain named BA.1 that struck last winter — and tested them in people. Those earlier recipe changes were safe, and the BA.1 version substantially boosted virus-fighting antibodies — more than another dose of the original vaccine — although fewer that recognized today’s genetically distinct BA.4 and BA.5 strains.

But instead of using those BA.1 shots, FDA ordered the companies to brew even more up-to-date doses that target those newest omicron mutants, sparking a race to roll them out. Rather than waiting a few more months for additional human studies of that very similar recipe tweak, Marks said animal tests showed the latest update spurs “a very good immune response.”

“One needs to refresh the immune system with what is actually circulating,” Marks said. That’s why FDA also is no longer authorizing boosters made with the original recipe for those 12 and older.

The hope, Marks said, is that a vaccine matched to currently spreading variants might do a better job fighting infection, not just serious illness, at least for a while.

What’s next? Even as modified shots roll out, Moderna and Pfizer are conducting human studies to help assess their value, including how they hold up if a new mutant comes along.

And for children, Pfizer plans to ask FDA to allow updated boosters for 5- to 11-year-olds in early October.

It’s the first U.S. update to the COVID-19 vaccine recipe, an important but expected next step — like how flu vaccines get updated every year.

And the U.S. isn’t alone. Britain recently decided to offer adults over 50 a different booster option from Moderna, a combo shot targeting that initial BA.1 omicron strain. European regulators are considering whether to authorize one or both of the updated formulas.

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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 vaccine, not one updated to better match the extra-contagious delta variant.

And that has some experts wondering if the booster campaign is a bit of a missed opportunity to target delta and its likely descendants.

“Don’t we want to match the new strains that are most likely to circulate as closely as possible?” Dr. Cody Meissner of Tufts Medical Center, an adviser to the Food and Drug Administration, challenged Pfizer scientists recently.

“I don’t quite understand why this is not delta because that’s what we’re facing right now,” fellow adviser Dr. Patrick Moore of the University of Pittsburgh said last week as government experts debated whether it’s time for Moderna boosters. He wondered if such a switch would be particularly useful to block mild infection.

The simple answer: The FDA last month OK’d extra doses of Pfizer’s original recipe after studies showed it still works well enough against delta — and those doses could be rolled out right away. Now the FDA is weighing evidence for boosters of the original Moderna and Johnson & Johnson vaccines.

“It’s less churn and burn on the manufacturing” to only switch formulas when it’s really necessary, said FDA vaccine chief Dr. Peter Marks.

But Pfizer and Moderna are hedging their bets. They’re already testing experimental doses customized to delta and another variant, learning how to rapidly tweak the formula in case a change eventually is needed — for today’s mutants or a brand new one. The tougher question for regulators is how they’d decide if and when to ever order such a switch.

What we know so far:

CURRENT VACCINES ARE WORKING EVEN AGAINST DELTA

Vaccines used in the U.S. remain strongly effective against hospitalization and death from COVID-19, even after the delta variant took over, but authorities hope to shore up waning protection against less severe infection and for high-risk populations. Studies show an extra dose of the original formulas revs up virus-fighting antibodies that fend off infection, including antibodies that target delta.

MIGHT A DELTA-SPECIFIC BOOSTER WORK EVEN BETTER?

Vaccines target the spike protein that coats the coronavirus. Mutations in that protein made delta more contagious but to the immune system, it doesn’t look all that different, said virus expert Richard Webby of St. Jude Children’s Research Hospital.

That means there’s no guarantee a delta-specific booster would protect any better, said University of Pennsylvania immunologist John Wherry. Waiting for studies to settle that question — and if necessary, brewing updated doses — would have delayed rolling out boosters to people deemed to need them now.

Still, because delta is now the dominant version of the virus worldwide it almost certainly will be a common ancestor for whatever evolves next in a mostly unvaccinated world, said Trevor Bedford, a biologist and genetics expert at the Fred Hutchinson Cancer Research Center.

A delta-updated vaccine would “help to provide a buffer against those additional mutations,” he said. Bedford is paid by the Howard Hughes Medical Institute, which also supports The Associated Press Health and Science Department.

TWEAKING THE RECIPE

The Pfizer and Moderna 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’s trained to recognize the virus. Updating the formula merely requires swapping out the original genetic code with mRNA for a mutated spike protein.

Both companies first experimented with tweaked doses against a mutant that emerged in South Africa, the beta variant, that has been the most vaccine-resistant to date, more so than the delta variant. Lab tests showed the updated shots produced potent antibodies. But the beta variant didn’t spread widely.

Now the companies have studies underway of fully vaccinated people who agreed to test a booster dose tweaked 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.

The mRNA vaccines are considered the easiest kind to tweak but some other vaccine makers also are exploring how to change their recipes if necessary.

WHY STUDY UPDATED SHOTS IF THEY’RE NOT YET NEEDED?

Moderna’s Dr. Jacqueline Miller told an FDA advisory panel last week the company is studying variant-specific boosters now to learn if they offer advantages, and to be ready if they’re needed.

And Penn’s Wherry said it is critical to carefully analyze how the body reacts to updated shots because the immune system tends to “imprint” a stronger memory of the first virus strain it encounters. That raises questions about whether a subtly different booster would prompt a temporary jump in antibodies the body’s made before — or the bigger goal, a broader and more durable response that might even be better positioned for the next mutations to come along.

NO RULES YET FOR MAKING A SWITCH

“What is the tripping point?” asked Webby, who is part of a World Health Organization network that tracks influenza evolution. “A lot of what is going to need to go into that decision making is just going to be learned by experience, unfortunately.”

Bedford said now is the time to decide what drop in vaccine effectiveness would trigger a formula change, just as is done with flu vaccines every year.

That’s important not just if a dramatically worse variant suddenly develops. Like many scientists, Bedford expects the coronavirus to eventually evolve from a global crisis into a regular threat every winter — which might mean more regular boosters, maybe even yearly in combination with the flu shot.

Timing between shots matters, too, Wherry noted.

“Your boostability may actually improve with longer intervals between stimulation,” he said. While scientists have learned a lot about the coronavirus, “the story’s not finished yet and we don’t know what the last chapters say.”

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The HCoV-Peptide array developed by CII scientists consists of 3 million immune markers on a glass chip, covering proteins of all known human coronaviruses, including the SARS-CoV-2. In collaboration with a team at Sun Yat-Sen University, the CII researchers identified 29 immune signatures specific to SARS-CoV-2. These genetic fingerprints (peptides) provide the blueprint for tests that will be used for diagnostics and surveillance. Current antibody tests for SARS-CoV-2 infection may generate false-positive results because of cross-reactivity with seasonal coronaviruses responsible for the common cold, as well as MERS-CoV and SARS-CoV-1.

To develop the HCoV-Peptide array, the researchers first analyzed blood samples taken from individuals with asymptomatic, mild, or severe SARS-CoV-2 infections, and controls including healthy individuals and those exposed to SARS-CoV-1 and seasonal coronaviruses. An analysis of all approximately 170,000 peptides related to known human coronaviruses yielded 29 peptides with the strongest and most specific reactivity with SARS-CoV-2. Next, they validated their test using a second set of blood samples, including those from confirmed cases of SARS-CoV-2, those with antibodies to other human coronaviruses, and healthy individuals.

The new test has a 98 percent specificity and sensitivity. Immune signatures were present from eight days after onset of COVID-19 symptoms to as long as six to seven months after infection.

“This work will allow us and others to build inexpensive, easy-to-use blood tests that can provide data for exposure as well as immunity,” says author Nischay Mishra, PhD, assistant professor of epidemiology at the Columbia Mailman School.

“This work with our colleagues at SunYat-Sen, led by Professor Jiahai Lu, and with Nimble Therapeutics, underscores the importance to public health of global collaboration and partnerships with industry in addressing the challenges of the COVID-19 pandemic,” says senior and corresponding author W. Ian Lipkin, MD, director of CII and John Snow Professor of Epidemiology.

Previously, the researchers have used similar methods to develop tests for Zika, acute flaccid myelitis, and tick-borne infections.

Co-authors also include Shreyas Joshi, Cheng Guo, James Ng, Riddhi Thakkar, Adrian Caciula, Rafal Tokarz, and Thomas Briese at CII; Xi Huang, Yongjian Wu, Xin Dong, Qianlin Li, and Jiahai Lu at Sun Yat-sen University, Guangzhou, China; and Richard Pinapati and Eric Sullivan at Nimble Therapeutics Inc, Madison, WI. Nischay Mishra, W. Ian Lipkin, Rafal Tokarz, Shreyas Joshi, Cheng Guo, and Thomas Briese are listed as the inventors on a patent filed that is related to findings in this study.

Research at Columbia was supported by the Chau Hoi Shuen Foundation and the Marin Community Foundation. Work at Sun Yat-Sen was funded by the Guangdong Scientific and Technological Research for COVID-19 (202020012612200001) and the National Science and Technology Major Project (No. 2018ZX10101002-001-001).

Publichealth.columbia.edu • Contributed

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