Mixing different brands of coronavirus vaccines for first and second dose, results in good protection against the virus, a UK study has found.
The Com-Cov trial looked at the efficacy of either two doses of Pfizer, two of AstraZeneca, or one of them followed by the other.
All combinations worked well to equip the immune system. This knowledge could offer flexibility for vaccine rollout, say experts.
The trial results also hinted that people who have already received two doses of AstraZeneca vaccine could have a stronger immune response if they were given a different jab as a booster if recommended in the autumn.
Some countries are already 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, following concerns about rare but serious blood clots, rather than about efficacy.
Two doses are important to give the fullest protection and teach the body to make antibodies and T cells to block and kill Covid.
The trial looked at giving the doses four weeks apart in 850 volunteers aged 50 and above, it found:
– The AstraZeneca (Covishield) followed by Pfizer induced higher antibodies and T cell responses than Pfizer followed by AstraZeneca
– Both of these mixes induced higher antibodies than two doses of AstraZeneca
– The highest antibody response was seen after two doses of Pfizer, and the highest T cell response from AstraZeneca followed by Pfizer
Lead investigator Prof Matthew Snape, from the University of Oxford, said the findings did not undermine the policy of giving people the same jab twice, but showed mixed dose schedules were also effective.