A mix and match of two different doses of Covid-19 vaccines offers good immune protection from coronavirus, a new UK study found this week.
The Com-Cov trial, led by the University of Oxford, has been investigating the immune responses of volunteers given a dose of the Oxford/AstraZeneca vaccine followed by the Pfizer/BioNTech jab, and vice versa, since February. It found that people who received the AstraZeneca vaccine first, followed four weeks later by a Pfizer dose, produced antibody levels nine times higher than those given two doses of the Oxford jab. Volunteers who were given Pfizer first and AstraZeneca second had antibody levels five times higher than those who received two doses of the Oxford vaccine. Medical experts say the latest findings offer hope for greater flexibility for vaccination programmes around the world.
"When it comes to the coming winter, if a third dose was to be given, then these are really important data to inform which vaccines we should be using and which combinations we should be using,” said Professor Matthew Snape, the Lead Investigator from the Oxford Vaccine Group.
"From our study you have to be thinking that if you received AZ/AZ (for the first and second doses) then maybe there would be advantages in getting an RNA vaccine (Pfizer or Moderna) next," he said.
Two doses of the Pfizer jab produced the highest antibody levels, but the T-cell response, which puts up a fight against the virus, was higher in people receiving the combination of vaccines.
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England’s deputy chief medical officer, Professor Jonathan Van-Tam, said the UK would stick to its current rollout using the same vaccine for the first and second dose.
"Given the UK's stable supply position there is no reason to change vaccine schedules at this moment in time," he said.
Meanwhile, a separate preprint study by the University of Oxford, found that a long interval between first and second doses of the AstraZeneca vaccine does not compromise the immune response after a late second dose.
When examining the effects of a delay of up to 45 weeks between first and second doses in study participants, results demonstrated that antibody levels were increased after a delayed second dose. Additionally, it would seem a longer delay between first and second doses may be beneficial, resulting in an increased antibody titre and enhanced immune response after the second dose.
“This should come as reassuring news to countries with lower supplies of the vaccine, who may be concerned about delays in providing second doses to their populations. There is an excellent response to a second dose, even after a 10-month delay from the first,” said Professor Sir Andrew Pollard, Professor of Paediatric Infection and Immunity and Lead Investigator of the Oxford University trial of the vaccine.
The findings also indicate that a third dose of the vaccine continues to boost antibodies against COVID-19. Some countries such as the UK are considering administering a third “booster” dose in the future. Studying the impact of a third vaccine dose, the researchers found that antibody levels increased significantly with a third dose. T-cell response and the immune response against variants were also boosted.
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“It is not known if booster jabs will be needed due to waning immunity or to augment immunity against variants of concern,” says Associate Professor Teresa Lambe OBE, lead senior author for these studies.
“Here we show that a third dose of ChAdOx1 nCoV-19 [Oxford/AstraZeneca] is well tolerated and significantly boosts the antibody response. This is very encouraging news, if we find that a third dose is needed,” she said.
Side effects of the vaccine itself were also found to be well-tolerated, with lower incidents of side effects after second and third doses than after first doses.
The university said that further research is required to follow up with study participants who received third doses beyond the period that was part of the initial study.
