Data shows two doses of Oxford/AstraZeneca vaccine provoked good immune response

Oxford University’s COVID-19 vaccine candidate has a better immune response when a two full-dose regime is used rather than a full-dose followed by a half-dose booster, the university said on Thursday, citing data from early trials.

The developers of the vaccine candidate, which has been licensed to pharmaceuticals company AstraZeneca, have already published later stage trial results showing higher efficacy when a half dose is followed by a full dose, compared to a two full-dose regime. However, more work needs to be done to affirm that result.

The latest details from the Phase I and 2 clinical trials released on Thursday made no reference to the half-dose/full-dose regime, which Oxford has said had been “unplanned” but approved by regulators.

Once seen as the frontrunner in the development of a coronavirus vaccine, the British team has been overtaken by U.S. drugmaker Pfizer, whose shots have been rolled out in Britain and the United States this month.

Data published earlier from the later Phase 3 trials showed efficacy was 62% for trial participants given two full doses, but a more robust 90% for a smaller sub-group given first a half, then a full dose.

In its statement on Thursday, the university said it had explored two dosing regimes in early stage trials, a full-dose/full-dose regime and a full-dose/half-dose regime, investigated as a possible “dose sparing” strategy.

“The booster doses of the vaccine are both shown to induce stronger antibody responses than a single dose, the standard dose/standard dose inducing the best response,” the university said in a statement.

The vaccine “stimulates broad antibody and T cell functions,” it said.