3 might be the magic number for COVID-19 vaccine doses, Yale immunologist explains

The Biden administration is reportedly preparing to announce that most vaccine-eligible Americans should get a COVID-19 booster shot after eight months. Allowing booster shots for all Americans, not just those with weak immune systems, would be a little controversial, since the 200 million doses of vaccine might be better used in countries with little supply and fewer vaccinated people. But there's also the question of what happens next? Will the COVID-19 vaccine become an annual thing, like the flu shot?

Actually, "three really could prove to be the magic dosing number — if the coronavirus remains relatively stable," Renuka Rayasam writes at Politico. "Even though Delta is more infectious than previous variants, it's still the same virus as the original COVID strain. A third vaccine dose this fall wouldn't be a different formulation than the first two — your body just needs more of it. The hepatitis B vaccine, for example, requires three doses for lasting immunity.

All vaccines lose a little efficacy over time, and if it weren't for the Delta variant, there would likely be no need for boosters at all, Akiko Iwasaki, a professor of immunobiology at Yale School of Medicine, tells Politico. The Pfizer and Moderna vaccines are proving to hold up well against COVID-19, but the Delta variant carries 1,000 times the viral load as the original strain and therefore needs more vaccine to ward off serious illness, she said. If the virus mutates to the extent the vaccines aren't effective, like the flu virus continues to do, then we may need more than just three doses eventually.

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"I just learned to be very humble with this virus because it comes up with different tricks," Iwasaki said. "It is still trying to find its sweet spot."