Oxford University Reports COVID-19 Vaccine Induced More Antibodies in Early Trials as Two Full Doses

Oxford University released new trial data last week that raises further questions about the most effective dosing regimen for Oxford’s COVID-19 vaccine candidate, AZD1222, that is being co-developed with AstraZeneca and how it came to pass that two different dosing regimens were pursued.

In a study published in the journal Nature Medicine, the Oxford researchers revealed that results from phase 1/2 trials showed that two full doses of the vaccine induced a stronger antibody response than one full dose and one-half dose. Efficacy was not measured in the phase 1/2 trials.

The study makes no reference to data from Oxford’s ongoing phase 3 trial released earlier this month, but phase 3 data from the UK and Brazil trials showed that a two-dose regimen with one half dose — administered after a fortuitous error in dose measurement — followed by one full dose, showed 90 percent efficacy for one group of participants, while those who received two full doses showed only 62 percent efficacy.

Oxford says the phase 1/2 study results justified its decision to proceed to phase 3 trials to evaluate the vaccine’s efficacy at two full doses. The university had previously explained that it had told regulators about the unplanned phase 3 half-dose and received permission to update the trial protocol to follow the group receiving the low-dose followed by full-dose regimen (DID, Dec. 10).

But shifting trial protocols when phase 3 efficacy trials are already well under way could impact the gathering of supporting data for an approval or Emergency Use Authorization. The FDA has said it will consider any vaccine that shows at least 50 percent efficacy, which means either regimen could qualify.

AstraZeneca is leading the phase 3 U.S. trial of the vaccine and is expected to release efficacy data in January (DID, Dec. 4). Oxford has declined to comment on the progress of the U.S. trial, which suggests that the university may be distancing itself from the stance AstraZeneca has taken regarding the explanation for the one-and-a-half-dose approach. AstraZeneca has maintained that the one-and-a-half dose regimen was the result of a measurement error.

Access the Nature Medicine study here: https://go.nature.com/3pb4FiM. ― Jason Scott