Pfizer Vaccine’s Effect on Transmission Still Unknown, FDA Says

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Pfizer Inc.’s Covid-19 vaccine prevents symptomatic cases of the virus, but it’s not clear if the shot keeps the disease from being transmitted, U.S. Food and Drug Administration staff found in a report issued Tuesday.

The conclusion highlights a major unknown about vaccine candidates that persists ahead of an ambitious U.S. rollout of millions of shots: How effective they’ll be in stemming the spread of coronavirus at a population level.

The answer to that question carries important implications for the continued use of public-health measures including masks and social distancing, even among those who have been immunized.

Because the shots from Pfizer and its German partner BioNTech SE avert symptomatic cases of Covid-19, their wide use could prevent virus transmission, the FDA staff report said. But if the vaccine doesn’t work as well in infections that lack symptoms, those cases “in combination with reduced mask-wearing and social distancing could result in significant continued transmission,” according to the staff report.

The FDA report was issued ahead of a Thursday meeting of outside advisers to the agency, whose deliberations will inform whether the vaccine is cleared for U.S. use.

Pfizer expects to report data on whether or not its vaccine stops virus transmission in the first quarter of 2021, Chief Executive Officer Albert Bourla said on Tuesday at a press briefing held by the International Federation of Pharmaceutical Manufacturers & Associations.

©2020 Bloomberg L.P.

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