WASHINGTON — Vaccine experts convened at a conference Thursday to debate how future Covid-19 booster shots should be designed to ensure that they provide protection against not only known variants but variants that have yet to emerge.
It's become the million-dollar question as omicron and its growing family of subvariants have dealt a significant blow to the protection provided by the existing vaccines from both Pfizer-BioNTech and Moderna.
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The drugmakers, as well as outside researchers and government scientists, met to discuss the topic at the World Vaccine Congress meeting in Washington, D.C., on Thursday.
All agree that the shots should be updated to ensure they can continue to provide protection against severe illness, but there isn't yet a broad consensus on what the best approach should be moving forward.
The most popular idea floated was developing a so-called pancoronavirus vaccine — a shot that could protect against the entire spectrum of strains of the virus, both known and unknown.
The coronavirus that causes Covid-19 is part of a family of coronaviruses called betacoronaviruses. The coronaviruses that caused SARS and MERS are also in this family.
But betacoronaviruses are just one branch in the broader coronavirus family tree. There are also alphacoronaviruses, gammacoronaviruses and deltacoronaviruses.
A pancoronavirus vaccine would essentially target the trunk of the tree, providing protection against all of the branches.
Still, a pancoronavirus could be years away. A similar vaccine, for influenza, still hasn’t been successfully developed.
Such a vaccine could provide "benefits in terms of durability and breadth,” Dr. Kayvon Modjarrad, a vaccine expert and director of Walter Reed's infectious diseases branch, said Thursday during a panel discussion on the topic.
Modjarrad, along with his colleagues at Walter Reed, are working to develop a pancoronavirus vaccine. A preclinical study published in December found the shot protected rhesus macaques against disease caused by the original strain of the coronavirus and produced antibody responses against variants of concern.
Trials in humans are currently underway.
The pancoronavirus vaccine is a different approach than what Pfizer and Moderna are currently pursuing.
Both companies are currently running clinical trials testing variant-specific or bivalent vaccines, which would target the dominant strain or strains circulating.
Moderna, in particular, has said its ideal vaccine candidate for the fall would be a bivalent shot that targets the omicron variant as well as the original coronavirus strain in a single shot.
But as new and often more contagious versions of the coronavirus emerge every couple of months, experts argued at the conference that that approach may not be a sustainable strategy long term.
Instead, scientists should focus on developing a vaccine that can protect against a wide variety of coronaviruses, no matter what variant may arise.
A long way to go
While a tantalizing idea, some experts said the public may still need to temper its expectations about what sorts of protection it expects a pancoronavirus to provide.
The existing mRNA vaccines still provide a high level of protection against severe illness, for example, but it has become evident that their protection against infection fades over time.
We can't just say "we’re going to develop a pancoronavirus that protects against infection," said In-Kyu Yoon, the acting director of the Coalition for Epidemic Preparedness Innovations, told his colleagues. "It’s just too unrealistic, for now."
Protection against infection comes from high antibody levels, but these tend to wane after several months. But other parts of the immune system, such as T cells, may persist for years. While not as fast-acting as antibodies, they come in after an infection to prevent severe illness.
And if and when such a vaccine is developed, the technology behind the new shot would still need to be simple enough for manufacturers to produce at a mass scale.
The mRNA shots from Pfizer and Moderna were praised by most doctors, researchers and scientists, in part because they could be tested and manufactured within several months, compared with traditional vaccines, which can take years.
But the technology behind the mRNA vaccines is much newer, meaning many facilities don’t have the capabilities to produce them. A more traditional vaccine, on the other hand, could be easier to scale.
It won't work if the shot "can’t be manufactured reproducibly," said Sriram Sathyanarayanan, chief scientific officer at biotech firm Codiak BioSciences. "We have to keep the construct simple enough for us to be able to manufacture."
And the new vaccine can't be made without one critical resource: money.
"You still have to have incentives for the manufacturers to invest into having a ready stockpile," Dr. Maria Bottazzi, co-director of the Texas Children’s Hospital Center for Vaccine Development at Baylor College of Medicine in Houston. Bottazzi helped develop another Covid shot that was authorized in India and uses older vaccine technology.
Scientists can "create the great technology but we have to see how it can be financed," Bottazzi said.
Modjarrad, of Walter Reed, mentioned the development of the vaccine could mirror Operation Warp Speed, the public-private initiative that helped create the current Covid vaccines from Pfizer and Moderna.
The strategy could incentivize drugmakers to develop shots for variants and other threats that "don’t quite exist yet," he said.
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