Oxford hired an outside manufacturer to produce large quantities of the vaccine for the trial. When the researchers received a sample of the vaccine and measured its strength, they noticed something strange. Using a different measurement technique than the manufacturer, Oxford found that the concentration of virus particles in the vaccine was twice that of the manufacturer.
Oxford researchers didn’t know which measurement to trust. They opted for a lower strength dose. In this way the dosage was safe even if it was incorrectly measured, albeit smaller than originally intended.
Participants were given two injections, about a month apart. Oxford started giving the vaccine. Within a few days, the participants reported fewer side effects such as sore arms or a mild fever than the participants during the first attempt. The Oxford researchers later identified an ingredient in the third-party vaccine batch that had moved their measurement up. That confirmed that they were using half a dose.
If the confusion about dosage surfaced months later, it would make efforts by scientists and public health officials more difficult to understand how well the vaccine was working.
Meanwhile, health officials began to advocate the inexpensive, easy-to-make vaccine. In June, Soumya Swaminathan, the chief scientist of the World Health Organization, called it “probably the leading candidate”. In July, UK Government Vaccine Task Force Leader Kate Bingham told lawmakers that it was “the most advanced vaccine in the world”.
Trump administration officials were also enthusiastic. White House Chief of Staff Mark Meadows told Congress leaders on July 30 that the Oxford-AstraZeneca vaccine could get emergency FDA approval as early as September, two people told the New York Times. (A spokesman for Mr. Meadows denied having discussed AstraZeneca’s prospects.)
Such optimism was premature.
Federal health officials said in June that in order to approve a vaccine, the FDA will likely need to see data from at least 30,000 late-stage study participants. At that point, Oxford’s studies in the UK and Brazil were ongoing, and even if their results were pooled, they would be below that FDA threshold. (The agency has never closed the door to relying solely on data from overseas studies when approving a vaccine.)