The use of the vector-based vaccine against AstraZeneca’s COVID-19 was discontinued for people under the age of 65 due to safety concerns, so all Swedish individuals already receiving the first dose of this vaccine were 2 The mRNA vaccine was recommended for the second time. dose.
Professor Peter Nordstrom of Umeå University in Sweden said:
“But our study shows that the risk for people who receive the mRNA vaccine after receiving the first dose of the vector-based vaccine is significantly reduced compared to those who received the vector-based vaccine at both doses. Shows, “said Nordstrom.
Published in The Lancet Regional Health-Europe Journal on Monday, the study is based on national registration data from the Swedish Public Health Agency, the National Health and Welfare Commission, and Statistics Sweden.
The main analysis included about 700,000 individuals. During an average follow-up of 2.5 months after the second dose, this study showed a 67% lower risk of infection with AstraZeneca plus AstraZeneca. Pfizer Vaccination.
The researchers said the risk of transmission from AstraZeneca and Moderna vaccination was 79% lower than that of unvaccinated individuals.
They said the risk reduction was 50 for those who received two doses of the AstraZeneca vaccine, known in India as the Cobishield.
These risk estimates were observed after considering differences in vaccination dates, age of participants, socioeconomic status, and other risk factors for COVID-19.
The researchers noted that study estimates of efficacy apply to infections with delta mutants that dominated the cases identified during the follow-up period.
“The results of this study can influence vaccination strategies in different countries,” said Marcel Valin, a PhD student and co-author of the study at Umeå University.
“The World Health Organization needs larger studies to investigate its safety and efficacy against clinical outcomes, despite promising results from previous studies on the immune response of mixed-and-match vaccination. There is one such study here, “said Barin.
According to the researchers, the incidence of adverse thromboembolic events, or the formation of blood clots in blood vessels, was very low on all vaccination schedules.
The number of COVID-19 cases severe enough to result in hospitalization was too small for researchers to calculate their effectiveness for this result.
Past studies have shown that a combination vaccine schedule produces a strong immune response.
However, it is unclear how much these schedules can reduce the risk of clinical infection, the researchers said, adding that their study aims to bridge that knowledge gap.