Astra Pares Covid Vaccine Efficacy Data After U.S. Criticism

AstraZeneca Plc reported a slightly lower efficacy rate for its Covid-19 vaccine after the results of an American clinical trial were criticized as outdated, raising further questions over the embattled shot and potentially delaying its approval in the U.S.

The vaccine was 76% effective at protecting volunteers against the coronavirus, the U.K. drugmaker said in a statement on Thursday. That compares with an earlier estimate of 79%, which was based on data gathered through Feb. 17.

The latest twist created another layer of uncertainty for a product already facing dwindling support in Europe following months of confusion and missteps. Although the vaccine is still expected to play a crucial role in curbing the global pandemic as governments around the world have ordered millions of doses, the repeated blunders risk further eroding public confidence in the immunization.

“The difference between 76% and 79% is a rounding error, probably just a handful of cases,” said Paula Cannon, a professor of molecular microbiology and immunology at the University of Southern California’s Keck School of Medicine, where she leads a research team that studies viruses. “But it’s so important for us to be completely transparent and accurate because we are building public trust.”

The findings were based on 190 symptomatic cases that developed among the 32,449 volunteers who participated in the trial, which includes 49 cases that weren’t counted as part of the initial analysis. The company didn’t disclose how many of those infections occurred in the group that received the vaccine and how many in the one administered a placebo.

There are another 14 people with probable or possible infections, so the total number of cases may still change — which may cause the overall efficacy rate to adjust again.

Too Rushed?

Astra shares were little changed in London trading. The Cambridge, England-based company emphasized that the marginal changes in protection rate did not detract from the vaccine’s overall efficacy.

“The primary analysis is consistent with our previously released interim analysis, and confirms that our Covid-19 vaccine is highly effective in adults,” said Mene Pangalos, the company’s executive vice president of BioPharmaceuticals research and development.

“We look forward to filing our regulatory submission for Emergency Use Authorization in the U.S. and preparing for the roll-out of millions of doses across America,” he said.

Some of Astra’s challenges reflect the unprecedented urgency of Covid-19 vaccine development, in which years-long processes have been compressed into several months.

“The problem with AstraZeneca is that they have had a couple of black eyes,” said Cannon. “I don’t think it’s malicious, it just reflects trying…