AZ-mRNA vax combo highly effective: Lancet study

LONDON: People who received a first dose of the Oxford-AstraZeneca (AZ) Covid-19 vaccine followed by an mRNA vaccine shot had a lower risk of infection compared to those immunised with both doses of the AZ preventive, according to a nationwide study in Sweden.
Since the use of AZ’s vector-based vaccine was halted for people younger than 65 years of age due to safety concerns, all individuals in Sweden who had already received their first dose of this vaccine were recommended an mRNA vaccine as their second dose.
“...Our study shows a greater risk reduction for people who received an mRNA vaccine after having received a first dose of a vector-based, as compared to people having received the vector-based vaccine for both doses,” said Peter Nordstrom of Umea University. The study was published in Lancet Regional Health - Europe journal on Monday. In the main analysis, about 7,00,000 individuals were included. During a 2.5-month average follow-up period after the second dose, the study showed a 67% lower risk of infection for the combination of AZ and Pfizer shots. There was a 79% lower risk of infection for AZ and Moderna shots, compared to unvaccinated individuals, the researchers said. For people having got two doses of the AZ vaccine (Covishield in India), the risk reduction was 50%, they said.
The researchers noted that the study estimates of effectiveness apply to infection with the Delta variant, which was dominating the confirmed cases during the follow-up period.“The results of the study may have implications for vaccination strategies in different countries,” said Marcel Ballin, doctoral student at Umea University, and study’s co-author. There was a very low incidence of thromboembolic events, or blood clots in blood vessels.