Mixing COVID-19 vaccines produces higher antibodies, T cell responses, claims UK study

A UK study has found that a mix-and-match approach to COVID-19 vaccines using different brands of jab for the first and second doses results in good protection against the Coronavirus. The study, Com-Cov trial observed the efficacy of either two doses of Pfizer, two of AstraZeneca, or one of them followed by the other. The end result indicated that all combinations worked well, priming the immune system, as per the BBC. 

Mixing COVID-19 vaccines

According to experts, the knowledge could offer flexibility for the vaccine rollout. Even so, UK's deputy chief medical officer, Prof Jonathan Van-Tam, said there was no reason to change the current successful same dose vaccine schedules in the UK as vaccines were in good supply and helping to save lives. However, Van-Tam did mention that the method can be looked at in the future.

"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." said Prof Jonathan Van-Tam.

As of now, the standard two-dose process is being followed by most countries as it gives complete protection and enables the body to make antibodies and T cells to block and kill the deadly virus. However, many countries are also using mixed doses. Spain and Germany are offering the Pfizer or Moderna mRNA vaccines as a second dose to younger people who have already received a first dose of the AstraZeneca vaccine. This comes after a few but serious cases of blood clots, rather than about efficacy. 

The Com-Cov study which looked at giving the doses four weeks apart in 850 volunteers aged 50 and above also found out that the AstraZeneca jab followed by Pfizer induced higher antibodies and T cell responses than Pfizer followed by AstraZeneca. In both cases, it was found out that higher antibodies were produced than two doses of AstraZeneca, the report added. It further added that the highest antibody response was seen after two doses of Pfizer, and the highest T cell response from AstraZeneca followed by Pfizer, it said. Even so, Lead investigator Prof Matthew Snape, from the University of Oxford, said the findings do not affect the current policy of giving people the same jab twice.

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

Snape stated that the new results showed mixed dose schedules were also effective, even though the interval of four weeks studied was shorter than the eight to 12-week schedule most commonly used in the UK. "This longer interval is known to result in a better immune response," he added. Mixed dose trial results for a 12-week jab interval will be available next month.

With PTI Inputs