A safety board that oversaw the US clinical trial of AstraZeneca's COVID-19 vaccine warned that the results released by the company on Monday may have included "outdated and potentially misleading" data. In response, AstraZeneca said it would publish up-to-date results from its latest vaccine trial within 48 hours.

In a rare move, the National Institute of Allergy and Infectious Diseases (NIAID) released a statement early Tuesday, saying that the Data and Safety Monitoring Board (DSMB), which is monitoring the AstraZeneca vaccine trial, is concerned that the trial result may have included outdated information.

If the company did include such information, it "may have provided an incomplete view of the efficacy data", the NIAID said in the statement.

The DSMB, an independent group of health experts appointed by the National Institutes of Health to review clinical studies, also notified other federal health agencies and AstraZeneca directly of its concerns, according to National Public Radio.

Dr Anthony Fauci, President Joe Biden's chief medical adviser and director of NIAID since 1984, told the Financial Times that he had never seen that happen before. He said the data board wrote a "rather harsh note" to him and AstraZeneca.

"When they saw the release, they were quite upset," he told the Financial Times. "We felt it was essential that we, the NIH, needed to have some sort of response, otherwise it would look like we were covering something up."

Fauci also discussed the issue on ABC's Good Morning America and said that AstraZeneca's release was an "unforced error". He said that "the data are quite good, but when they put it into the press release, it wasn't completely accurate".

AstraZeneca, in its statement released Tuesday morning, said the data it released Monday included cases up to Feb 17, and it promised to update and reissue its trial results in 48 hours.

"We will immediately engage with the independent data safety monitoring board to share our primary analysis with the most up-to-date efficacy data. We intend to issue results of the primary analysis within 48 hours," the Cambridge, England-based company said.

The company said it had reviewed the preliminary assessment of its full, or primary analysis, and the results were consistent with the interim analysis. The company is now completing the validation of the statistical analysis.

The company's statement contradicts the NIAID concerns, which imply that data collected after Feb 17 changed the trial's findings on the vaccine's efficacy.

AstraZeneca reported Monday that its COVID-19 vaccine is 79 percent effective against symptomatic COVID-19 and has 100 percent efficacy against severe or critical disease and hospitalization.

The company said it was going to apply for emergency authorization from the Food and Drug Administration (FDA) by mid-April, so its vaccine, which is already being made in the US, could be available by the end of May.

The new doubts about the shot's efficacy cloud the timeline for its emergency-use authorization in the US.

The trial confusion also comes as 13 European countries temporarily suspended the AstraZeneca vaccine last week after reports of a handful of recipients reporting blood clots.

The European Medical Authority (EMA) investigated the concerns and declared on Thursday that the vaccine was safe and effective and was not linked with a rise in the overall risk of blood clots.

At the same time, Pfizer Inc announced an early-stage US trial of a new pill that could be used at the first sign of infection, the company said Tuesday.

Pfizer, which already has an authorized COVID-19 vaccine in the US with German drugmaker BioNTech, said the new oral antiviral drug, named PF-07321332, is a "protease inhibitor" that works by inhibiting an enzyme that the virus needs to reduplicate in human cells.

If the virus cannot replicate, then it cannot further infect the host. Lab studies have demonstrated potent antiviral activity against SARS-CoV-2 and other coronaviruses, Pfizer said.

"Tackling the COVID-19 pandemic requires both prevention via vaccine and targeted treatment for those who contract the virus," Pfizer's chief scientific officer, Mikael Dolsten, said in a statement. "Given the way that SARS-CoV-2 is mutating and the continued global impact of COVID-19, it appears likely that it will be critical to have access to therapeutic options both now and beyond the pandemic."