Nov. 26 (UPI) -- AstraZeneca and Oxford University responded Thursday to questions raised over trial results for its COVID-19 vaccine candidate.
The pharmaceutical company said Monday that its vaccine candidate, AZD1222, had an average efficacy of 70%.
Some in the scientific community questioned the results and the methods of the trial and criticized the way the company initially disclosed its data. The company said a mistake led to some trial participants receiving the initial dose at half strength.
On Thursday, AstraZeneca told CNBC that it adhered to the "highest standards" in its studies.
"More data will continue to accumulate and additional analysis will be conducted refining the efficacy reading and establishing the duration of protection," a spokesperson told the news outlet.
The questions emerged after a smaller group of 2,741 trial participants received a half dose of the vaccine initially followed by a full dose at least a month later, with results showing 90% efficacy. A second group of 8,895 participants received two full doses of the vaccine at least a month apart, with results showing 62% efficacy.
Oxford University attributed the lower dose to "a difference in the manufacturing process."
"The methods for measuring the concentration are now established and we can ensure that all batches of vaccines are now equivalent," Oxford said.
Some U.S. scientists, including Moncef Slaoui, chief of the White House vaccine effort, Operation Warp Speed, said the 90% efficacy result was only shown for low-risk participants younger than age 55.
An analyst from investment bank SVB Leerink said the company's trials didn't meet FDA requirements for populations at increased risk, including minorities, severe cases, previously infected individuals and elderly.
AstraZeneca said an external Data Safety Monitoring Board monitored the study for safety and quality.
The vaccine candidate is the third to announce preliminary results of late-stage trials. Pfizer and BioNTech and Moderna each reported early results showing 95% efficacy for their COVID-19 vaccine candidates.
Dr. Anthony Fauci, the nation's leading infectious diseases expert, has sought to reassure people to feel confident in the safety and efficacy of a COVID-19 vaccine once regulatory approval is granted.