KUALA LUMPUR, June 29 — Mixing Covid-19 vaccines made by Pfizer-BioNTech and AstraZeneca-Oxford produce a better immune response than two doses of AstraZeneca, a new UK study found.
Oxford University’s Com-Cov vaccine trial, which studied the use of different combinations of approved Covid-19 vaccines, discovered that a mixed two-dose schedule of the Pfizer and AstraZeneca vaccine can boost concentrations of antibodies against Covid-19 spike proteins.
This is true for any combination of the two vaccines — either Pfizer followed by AstraZeneca, or AstraZeneca followed by Pfizer — compared to two doses of the AstraZeneca vaccine. Two doses of the Pfizer vaccine produced the highest antibody response, whereas the highest T-cell response came from AstraZeneca followed by Pfizer.
A combination of a first dose with AstraZeneca followed by a second dose with Pfizer induced higher antibodies and T-cell responses than Pfizer followed by AstraZeneca, BBC reported.
The doses in the trial, however, were given four weeks apart, rather than the eight to 12-week schedule most commonly used for the AstraZeneca vaccine. UK officials have suggested an eight-week gap between doses for those aged over 40 and a 12-week gap for other adults.
“The results show that when given at a four-week interval both mixed schedules induce an immune response that is above the threshold set by the standard schedule of the AstraZeneca vaccine,” said Professor Matthew Snape, associate professor in paediatrics and vaccinology at the University of Oxford, and chief investigator on the trial, as quoted by CNBC.
He said the study is also looking at mixed studies over a 12-week interval, as the AstraZeneca shot is known to produce a better immune response with a longer interval between doses. The mixed dose trial results for a 12-week jab interval will be available next month.
Previous clinical trials showed that the longer gap between doses increased AstraZeneca’s vaccine efficacy to 82.4 per cent, compared to 54.9 per cent when the second dose was given less than six weeks after the first dose.
The latest Com-Cov findings, involving 850 volunteers aged 50 and above, could add flexibility to vaccination programmes around the world, Snape said.
Some countries have already opted for a mixed-dose approach, with Spain and Germany offering the Pfizer or Moderna mRNA vaccines as a second dose to people who received the AstraZeneca vaccine as their first dose — including German Chancellor Angela Merkel.
Meanwhile, another pre-print study suggests a third dose of the AstraZeneca vaccine, given more than six months after the second, could boost the immune system, reported the BBC.
BBC’s medical editor Fergus Walsh in an analysis noted that the results of the initial mix and match vaccine trial suggest that it may be preferable to give a different brand of vaccine for the third booster shot than the one used for the first two shots.
However, mixing vaccines could result in more short-term side effects such as chills, headaches and muscle pain.