What Pfizer's scientists consider the 'biggest surprise' about their COVID-19 vaccine

Pfizer vaccine.
(Image credit: ROBYN BECK/AFP via Getty Images)

The aspect of Pfizer's coronavirus vaccine that really stunned the company's scientists was the fact that vaccinated participants in the Phase 3 efficacy trial had protections against the pathogen by day 12, a time at which there was barely any antibody response, Stat News reports. "That was the biggest surprise," said Vidia Roopchand, Pfizer's principal scientist for viral vaccines.

Roopchand is still trying to figure exactly why that is — not that it's a bad thing — by poring over the data. One possibility is that other aspects of the immune system such as T-cells that Roopchand says have largely been neglected in immunology research may have played a significant role. It's possible, he suggested, that's more important to measure cellular immunity than look for a robust antibody response. "The 12-day protection data is telling us there's more to it," Roopchand told Stat. "This is a great time to learn."

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Tim O'Donnell

Tim is a staff writer at The Week and has contributed to Bedford and Bowery and The New York Transatlantic. He is a graduate of Occidental College and NYU's journalism school. Tim enjoys writing about baseball, Europe, and extinct megafauna. He lives in New York City.