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AstraZeneca will publish up-to-date results from its latest COVID-19 vaccine trial within 48 hours after U.S. health officials said the drugmaker’s analysis of the shot’s efficacy may not have been based on all the available data.

The rare public rebuke marks the latest setback for the vaccine which was hailed as a milestone in the fight against the COVID-19 pandemic but has since been dogged by questions over its effectiveness and possible side effects.

AstraZeneca said results it published on Monday giving the shot an efficacy rate of 79% were based on an interim analysis of data through Feb. 17 and it would now “immediately engage” with the panel monitoring the trial to share its full analysis.

The Anglo-Swedish drugmaker said on Tuesday it had reviewed the preliminary assessment of its full, or primary, analysis and found it to be consistent with the interim report.

Its shares were down 2.5% in London trading.

The U.S. National Institute for Allergy and Infectious Diseases (NIAID) said on Monday that the board charged with ensuring the trial’s accuracy had expressed concern the company may have given an incomplete view of the shot’s effectiveness.

Anthony Fauci, director of the NIAID, said the whole issue was a really unfortunate unforced error.

“This is very likely a very good vaccine and this kind of thing does ... nothing but really cast some doubt about the vaccines and may contribute to the hesitancy,” he told “Good Morning America” on ABC News.

“The data really are quite good but when they put it into the press release it wasn’t completely accurate,” he said. “We have to keep essentially trying as hard as we can to get people to understand that there are safeguards in place.”

‘NEGATIVE REPORTS’

Besides being 79% effective in stopping symptomatic illness in the trial in the United States, Chile and Peru, the data also showed the shot was 100% effective against severe or critical forms of the disease and posed no increased risk of blood clots.

The new doubts about the shot’s efficacy, however, coincide with its rollout in dozens of countries and clouds the timeline for its emergency use authorization in the United States.

“This is indeed an extraordinary act. The negative reports about this vaccine do not stop, although my assessment is that it is well tolerated and safe, but clearly less effective than the two mRNA vaccines,” Peter Kremsner, from the University Hospital in Tuebingen, Germany.

Rival vaccines from Pfizer/BioNTech and Moderna that use so-called mRNA technology produced efficacy rates of about 95% each, far above the 50% benchmark set by global regulators.

The panel monitoring the AstraZeneca trial, the Data and Safety Monitoring Board, is organized by NIAID and its role is to provide study oversight and evaluate clinical data to ensure safe and ethical conduct of the study.

AstraZeneca’s COVID-19 shot has faced questions since late last year when the drugmaker and Oxford University published data from an earlier trial with two different efficacy readings as a result of a dosing mistake.

Later analysis suggested the dosing interval rather than the amount of dose administered was responsible for the difference.

CONFIDENCE HIT

Confidence in the vaccine took a further hit this month when more than a dozen countries, mostly in Europe, temporarily suspended the shot after reports linked it to a rare blood clotting disorder in a very small number of people.

The European Union’s drug regulator said last week it was safe but an opinion poll on Monday showed Europeans remained skeptical about its safety.

The latest trial data, which has yet to be reviewed by independent researchers, was based on 141 infections among 32,449 participants.

Analysts had noted AstraZeneca’s achievement of producing strong trial data against a backdrop of more infectious variants spreading in the United States and other countries.

Stephen Evans, a pharmacoepidemiology professor at London School of Hygiene & Tropical Medicine, said the up-to-date data request may have to do with efficacy readings from recent cases, which may include new variants and thus lower protection rates.

“The other vaccines may also show such reduced efficacy and we don’t know by how much. It does not leave me concerned particularly unless they had found a safety issue that was being hidden, which does not appear to be the case.”

The AstraZeneca vaccine is seen as crucial in tackling the spread of COVID-19 across the globe because it is easier and cheaper to transport than rival shots.

It has been granted conditional marketing or emergency use authorization in more than 70 countries.

Many countries are relying heavily on it to end the pandemic, and several state leaders have taken the shot to boost confidence in the vaccine including South Korea’s President Moon Jae-in who received it on Tuesday.