What the new study says about the “mix” of the first and second doses of AstraZeneca and Pfizer vaccines, how effective they are, and how many have had serious side effects.
A Spanish COVID-19 vaccine combination study found that giving a single dose of Pfizer vaccine to people who have already received their first dose of AstraZeneca vaccine is safe and effective, according to preliminary results to date.
The Combivacs study, conducted by the state-sponsored Carlos III Health Institute, found that the presence of IgG antibodies in blood was 30 to 40 times higher in people who received a second dose of Pfizer vaccine than in a control group of people who received only one dose of AstraZeneca.
At the same time, the presence of neutralizing antibodies increased sevenfold after the administration of Pfizer, which is significantly higher than after the administration of the second dose of AstraZeneca.
The scientific study involved about 670 volunteers, aged 18 to 59, who had already been vaccinated with the first dose of AstraZeneca, and about 450 of them received the Pfizer vaccine.
According to one of the study’s authors, Dr. Magdalena Cobbins, 1.7% of the participants reported “serious side effects” that were limited to headaches, muscle pain, and some discomfort.
“These are not symptoms that can be considered serious,” the expert summed up.