Oxford University said on Thursday that its Covid-19 vaccine candidate has a better immune response when given in a two full-dose regime rather than a full-dose followed by a half-dose booster, Reuters reported.

“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, citing data of early stage trials. The vaccine “stimulates broad antibody and T cell [components of adaptive immune system] functions,” it said.

The university said it had explored two different dosing regimes in trials – a full-dose/full-dose regime and a full-dose/half-dose regime – as a possible “dose sparing” strategy.

The developers of the vaccine candidate have already published later stage trial results that show higher efficacy when a half dose is followed by a full dose compared to the other dosage regime. However, the trails need more work to guarantee that result.

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

Earlier in the month, data from later phase 3 trials revealed that the Oxford vaccine candidate, developed in collaboration with United Kingdom-based drugmaker AstraZeneca, showed 90% efficacy in a small group who got a half-dose first, but only 62% among them were given two full doses. The overall vaccine efficacy across both groups was 70.4%.

Experts, however, had expressed caution, saying that while the vaccine was safe and effective, AstraZeneca and Oxford University would have to do more work to achieve 90% efficacy as some other vaccine candidates have shown. In contrast, the Pfizer/BioNTech and Moderna vaccines both have efficacies above 90%.

Meanwhile, the coronavirus has infected more than 7.48 crore people and killed over 16.60 lakh globally, according to the Johns Hopkins University. Over 4.22 crore people have recovered from the infection.