As health officials anxiously track the new variants of COVID-19, the question is when do you start to worry about the virus making an end-run around the world's vaccines?
Even with the pace of vaccinations accelerating, some experts worry about a scenario where strains even more virulent than the one detected in South Africa start to emerge.
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They fear further coronavirus mutations that could potentially spread as quickly as the United Kingdom variant has.
"Then we have more trouble," says Dr. Catherine Blish, M.D., Ph.D. an infectious disease expert at Stanford. "Because then we have a partially resistant variant with a chance for it to develop more mutations and become even more resistant, and it could, hopefully not, but it's going to be a race with our vaccine delivery and those variants."
Pfizer and Moderna recently announced test results that suggest their vaccines are still currently protective against the South African strain, even though there were reductions in the number of antibodies created.
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Moderna may also be exploring a potential "third-dose" booster shot for its two-part regimen.
The Oxford-AstraZeneca pharmaceutical group, whose vaccine performed poorly against the South African variant, says it's working to produce an update by the fall.
Stanford infectious disease researcher Bali Pulendran, Ph.D., says modern RNA and virus-based vaccines have an advantage because their genetic formulas can be adjusted quickly.
"To generate a tweaked RNA vaccine I think is not an issue," Dr. Pulendran says. "Some companies are already thinking about doing it, and in fact, some may already be doing it. Same thing applies to viral vector vaccines."
Tweaking the vaccine composition might not mean researchers going back to the drawing board.
The Food and Drug Administration is finalizing plans for fast-track approval trials for new formulas that leveraging available clinical trial data.
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"No tens of thousands of people, a few hundred people who get this tweaked vaccine," Dr. Pulendran explains. "And you can measure the quantity of neutralizing antibody."
Other proposed strategies include possibly mixing and matching second doses from different vaccines.
Researchers say different vaccines may activate the immune system in slightly different ways, a process that could create a strong overall effect.
"And so we might gain some immunity to more than just that one little spike protein that sticks out," says Dr. Blish.
Many researchers believe current vaccines are in a solid position in the near term, in part because of the protection they offer against severe disease.
But health officials worldwide will likely be watching for what some have described as a dangerous red alert.
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The cause for alarm would be if vaccinated patients start turning up in hospitals with more severe infections.
The circumstance would also signal that tweaked vaccines may be needed to protect against a shifting threat.
Even with a successful vaccination program, many researchers expect COVID-19 vaccines to need regular updating every few years if we are to be ready for any future outbreaks.
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