People who got a first dose of Oxford-AstraZeneca’s Covid-19 vaccine followed by an mRNA vaccine had a lower risk of contracting Covid-19 than those who got both doses of the AstraZeneca vaccine, a study published in medical journal The Lancet showed on Sunday.

Messenger RNA vaccines, or mRNA vaccines, trigger an immune response by helping cells in the human body to make a protein that can offer protection against a pathogen. Pfizer and Moderna’s Covid-19 vaccines are examples of these.

The study was conducted by Peter Nordstrom and Anna Nordstrom, professors at Sweden’s Umea University, and Marcel Ballin, a doctoral student at the university. It was based on data collected from the Public Health Agency of Sweden and the Swedish National Board of Health and Welfare.

The study showed that those who were inoculated with the AstraZeneca vaccine followed by Pfizer had a 67% lower risk of infection than unvaccinated 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 analysed together, the vaccine schedules had an effectiveness of 68%. In comparison, those who were administered two doses of the AstraZeneca vaccines had a 50% lower risk of the 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 Moderna vaccines, and 4,30,100 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’s findings state that such mixing of vaccines “is an effective alternative to increase population immunity against Covid-19, including against the Delta variant which dominated the confirmed cases during the study period”.

Peter Nordstrom, however, noted that taking any approved vaccine is better than not taking any vaccine. He added that taking two doses was better than one, PTI reported.

Marcel Balin said that the results of the study can have implications for vaccination strategies in different countries.

“The World Health Organization has stated that despite the promising results from previous studies regarding immune response from mix-and-match vaccination, there is a need for larger studies to investigate their safety and effectiveness against clinical outcomes,” he said. “Here we now have one such study.”