AstraZeneca to Test If Longer Wait Between Vaccine Doses Works Better


AstraZeneca Plc plans to conduct a global study on the optimal interval between the two doses of its Covid-19 vaccine as questions linger over how to elicit the best protection for the greatest number of people.

The new trial will investigate a two-month gap between shots to determine whether it can provide better efficacy, Chief Executive Pascal Soriot told a group of European newspapers Tuesday. The U.K. approved the vaccine, developed with the University of Oxford, last month with a 4- to 12-week dosing interval.

The study supersedes the company’s plans to investigate different dosing levels, a spokesman said. Some countries are opting to delay the second injection of the vaccines available in an attempt to protect more people, while others shun the approach due to a lack of data.

Data from trials of the shot in the U.K. and Brazil raised questions after one arm of a study that received a half-dose followed by a full-dose of vaccine produced an efficacy of 90%, compared with 62% for two standard doses.

Higher Efficacy

A panel of scientists behind the U.K. approval said in December that the higher efficacy seen from the half-dose regimen could be attributed to the gap between injections rather than dosing levels.

“You get a better efficiency if you get the second dose later,” Soriot told the newspapers, including Italy’s La Repubblica. “We are going to do a study in the U.S. and globally to use two-month dose interval to confirm that this is indeed the case.”

Astra executive Mene Pangalos told a U.K. parliamentary committee earlier this month that further analysis of the trial data suggested an increased interval raised efficacy and that an 8- to 12 week gap looked to be the “sweet spot.”

More data from the company’s existing U.S. trial should also bring clarity on dosing intervals. Results are likely in March, according to Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. He spoke Wednesday at a press briefing with members of President Joe Biden’s Covid-19 response team.

Enrollment for the study is complete, with 32,459 people participating, of whom 26,327 had received their second dose by Jan. 21, according to data presented by Astra at a meeting of Centers for Disease Control and Prevention advisers Wednesday. Two-thirds of volunteers in the trial received the vaccine versus a placebo.

The U.S. study will also provide more data on the efficacy of the vaccine in older adults, after a lack of participants in the U.K. and Brazil trials left questions. About 24% of U.S. trial participants are aged 65 and over. Concerns over a lack of protection for this age group were raised this week after a German newspaper, citing unidentified sources in Germany’s ruling coalition, said Astra’s vaccine was only effective for 8% of people over 65.

New Strains

The German health ministry and Astra denied the report, with the company saying it was “completely incorrect.”

Andrew Pollard, the lead investigator on the U.K. Oxford trials, said at the CDC meeting that the university and Astra will have data on the efficacy of the vaccine against a variant of the virus first discovered in Britain within a “week or two.” The team is also looking at how effective the shot is against a variant linked to South Africa.

Separately, Astra has clashed with European Union officials over vaccine delays. EU regulators are expected to approve the Astra shot for use in the bloc later this week.

©2021 Bloomberg L.P.

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