People who received a first dose of Oxford-AstraZeneca Covid-19 vaccine followed by an mRNA vaccine had a lower risk of developing Covid-19 than those receiving both doses of the AstraZeneca vaccine, a study published in the medical journal The Lancet showed on Sunday.
Messenger RNA vaccines, or mRNA vaccines, trigger an immune response by helping cells in the human body make a protein that can offer protection against a pathogen. Pfizer and Modernas Covid-19 vaccines are examples of these.
The study was conducted by Peter Nordstrom and Anna Nordstrom, professors at Sweden’s Umeå University, and Marcel Ballin, doctoral student at the university. It was based on data collected from the Swedish Public Health Agency and the National Board of Health and Welfare.
The study showed that those inoculated with the AstraZeneca vaccine followed by Pfizer had a 67% lower risk of infection than non-vaccinated individuals. Those who received a combination of the AstraZeneca vaccine and the Moderna shot had a 79% lower risk of infection.
When these two groups were analyzed together, vaccine schedules had an efficiency of 68%. By comparison, those who received two doses of the AstraZeneca vaccine had a 50% lower risk of coronavirus infection.
The researchers studied a cohort of 94,569 people who received a combination of AstraZeneca and Pfizer vaccines, 16,402 people who received the AstraZeneca and Modern vaccines, and 4,301 people who received two doses of the AstraZeneca vaccine. The group also included 1,80,716 people who were unvaccinated at the time of the study.
The research results say that such a mixture of vaccines “is an effective alternative to increase the population’s immunity to Covid-19, including to the Delta variant that dominated the confirmed cases during the study period”.
Peter Nordström noted, however, that it is better to take an approved vaccine than not to take any vaccine. He added that it was better to take two doses than one, PTI reported.
Marcel Balin said that the results of the study may have consequences for vaccination strategies in different countries.
“The World Health Organization has stated that despite the promising results of previous studies on immune responses from mix-and-match vaccination, there is a need for larger studies to examine their safety and efficacy against clinical outcomes,” he said. “Here we now have such a study.”