U.S. Health Officials Raise Concerns Over AstraZeneca Vaccine Data

LONDON—U.S. officials said they were told AstraZeneca PLC may have released outdated information about trial results for its Covid-19 vaccine—a surprise disclosure that immediately cast doubt on the company’s assertion a day before that results showed the shot to be highly effective.

The early-morning statement from the National Institute of Allergy and Infectious Diseases came a day after AstraZeneca released interim data from large-scale U.S. trials that it said found its Covid-19 vaccine to be 79% effective in preventing symptomatic disease.

AstraZeneca, in its own statement, said it would update and reissue its trial results in 48-hours.

The results served as a short-lived vote of confidence in the shot, which has been clouded by uncertainty over previous, confusing efficacy results and large-scale production problems. More recently, reported cases of rare blood clotting in Europe raised concerns about the vaccine’s safety, though European regulators have recommended its continued use. The U.S. trials showed no link with the vaccine and the NIAID statement Tuesday didn’t raise questions about that finding or other safety-related issues.

Despite that reputational cloud, the shot is being rolled out widely outside the U.S., including across Europe where it is a key plank in efforts by governments there to accelerate its vaccination drive. Regulators there and in dozens of other countries have approved the shot for use. Early, real-world data from the U.K. has shown the vaccine to be effective in older recipients.