Mixing doses of COVID vaccines, be it AstraZeneca or Pfizer, does not necessarily mean you cover more ground in protecting yourself from the virus. On the other hand, you are more likely to suffer side effects such as chills, fevers, headaches and fatigue, according to a report published in medical journal The Lancet.
Researchers from the University of Oxford studied people who first took a dose of AstraZeneca’s vaccine, followed by one of Pfizer, four weeks later. While AstraZeneca has developed a ChAd vaccine (manufactured in India by Serum Institute under the Covishield brand), Pfizer has brought out an mRNA vaccine.
The typical side effects of COVID vaccines were more frequently reported in the study; but much of was it short-lived and mild, said the report, titled ‘Heterologous prime-boost COVID-19 vaccination: initial reactogenicity data’. For instance, about a tenth of participants had severe fatigue, vis-à-vis just 3% of those who took two shots of the same vaccine. When the doses were switched, too, the findings were similar.
“Participants are 50 years and older with no or mild-to-moderate, well controlled comorbidity and were recruited across eight sites,” said the Lancet report.
While a homologous schedule (two doses of the same vaccine) is universally recommended, a ‘mismatched’ dosage has also been frequently reviewed, particularly to address the shortage of vaccines in various regions. Public health officials and researchers are looking at how different vaccines may be blended to beat the scarcity and yet inoculate the population.
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If a study fully proves that such a heterologous schedule is effective and safe, it will ease the implementation burden for governments to a large extent.
While low-income nations typically bear the brunt of a supply shortage, some of the advanced nations, too, have been forced to address such an issue. For example, in France, a large number of people took the first jab of the AstraZeneca vaccine. But the government subsequently restricted it to older people, which meant the rest had to take the Pfizer vaccine for their second jab.
‘Intriguing and unexpected’
A Bloomberg report on the study quoted Matthew Snape, an Oxford paediatrics and vaccinology professor leading the trial, as calling the finding “intriguing”, and “not something that we were necessarily expecting”.
According to him, while the side-effects of a mixed programme may not be long lasting, it could result in more work absences post immunisation. “You wouldn’t want to immunize a ward full of nurses with a mixed schedule on the same day,” he said, according to Bloomberg.
Next, the researchers are looking at widening the interval between the shots to 12 weeks. They also plan to include the vaccines of Moderna and Novavax for the study.