Having mixed doses of COVID vaccines for first and second shots appears to boost immune response against the virus, according to an Oxford study.

In a Com-Cov trial, researchers looked at the impact of a mix-and-match approach to vaccinations where people were given of either two shots of AstraZeneca or Pfizer vaccine, or a combination of the two.

“You’ve certainly got an extra kick to your immune system if you boost with the RNA vaccine from Pfizer rather than a booster dose of the AstraZeneca vaccine,” said Matthew Snape, lead investigator on the Com-Cov trial, in The Guardian report.

“Based on what we’re seeing here, switching over to an RNA vaccine could have some benefits in terms of antibodies,” he added.

Experts also said the study could offer flexibility for vaccine rollout.

"Mixing doses could provide us with even greater flexibility for a booster programme, while also supporting countries who have further to go with their vaccine rollouts, and who may be experiencing supply difficulties," United Kingdom's deputy chief medical officer, Prof Jonathan Van-Tam said in a BBC report.

People who already have been inoculated with two doses of AstraZeneca vaccine could have a stronger immune response if they will be given a different shot as a booster if recommended in the autumn, the report added.

The results also found that AztraZeneca followed by Pfizer induced higher antibodies and T cell responses than Pfizer followed by AztraZeneca.

Both of these mixes induced higher antibodies than two doses of AztraZeneca, it added.

"We already know that both standard schedules are very effective against severe disease and hospitalizations, including against the Delta variant when given at eight to 12 weeks apart," Snape said.

Meanwhile, mixed dose trial results for a 12-week jab interval will be available next month, BBC reported.

The alternating of vaccines are already being used in several countries including Germany, Sweden, France, Spain, and Italy.

These countries are offering the Pfizer or Moderna mRNA vaccines to young people who had AstraZeneca vaccine as their first dose, after it has been linked to a rare blood clotting disorder.

In South Korea, the government announced that health workers who got their first dose of AztraZeneca could receive the Pfizer shot as a second dose following delivery delays.

The Philippines, meanwhile, expressed its openness to adopt findings from other countries once evidence or data is already available and complete.

The country earlier also said it is expecting to start the study on the efficacy of mixing and matching of five COVID vaccines namely, the Sinovac, Sputnik V, AstraZeneca, Pfizer, and Moderna, by next month.