Pfizer or AstraZeneca: What does the ECA study show about antibodies after vaccination?

Η Therapeutic Clinic of Faculty of Medicine of EKPA conducts a study of the kinetics of antibodies against the SARS-CoV-2 to volunteers who receive the approved vaccines from the Ministry of Health. The results of the comparison of neutralizing antibody production after administration of the vaccine of Pfizer or of AstraZeneca, in volunteers aged 60-64 years old (median age 61 years with both vaccines).

The age group was chosen because people aged 60-64 years were the first to be vaccinated with the AstraZeneca. The comparison was made with health workers who received the vaccine of Pfizer and were the same age and sex as those who received the vaccine for AstraZeneca.

In the study the production of neutralising antibodies was measured (as their name suggests, they are the ones that «neutralise» the virus), the existence of which at a level above 30% is indicative of virus inactivation, while levels above 75% indicate very high protection against the virus. They were measured on the day of the first dose of the vaccine (before vaccination), 3 weeks later (day 22, before the second dose of the vaccine for those who received the Pfizer vaccine), and then after 4 weeks (day 50 after the first dose of the vaccine).

Measurements are made with commercially available technologies approved by the Food and Drug Administration (FDA) of USA. The leaders of the study, Evangelos Terpos (Professor of Hematology at the University of Athens), John Trougakos (Professor of the Department of Biology of the University of Athens) and Thanos Dimopoulos (Rector of the University of Athens) summarize the most important results of the research.

The results of 78 people who received the vaccine for Pfizer with those of 73 volunteers who received the vaccine of AstraZeneca. Before the first dose of vaccines, there was no difference in the value of neutralizing antibodies between the two groups. On day 22, before the second dose of the vaccine of Pfizer, the 78% of vaccinees with the vaccine of Pfizer developed neutralising antibodies against the 56% of those who received the vaccine of AstraZeneca.

On the 50th day that the vaccine team of the Pfizer had already received the second dose of the vaccine and 4 weeks had passed, the difference was even greater. Overall, 98% of those vaccinated with the Pfizer vaccine developed neutralizing antibodies (almost all at levels above 75%) compared to 75% of those who received the AstraZeneca. In the vaccine group of AstraZeneca only 11% had neutralising antibody titres above 75%, 50 days after the first dose of vaccine. However, as shown by the results, an increase in the number of individuals with positive antibody titres was also observed with the AstraZeneca, between 3 and 7 weeks after the first dose of vaccine.

The study by the University of Athens shows that the effectiveness of vaccines is very high in the 60-64 age group. The second dose of the vaccines is necessary to achieve high titres of neutralising antibodies against SARS-CoV-2.

The results with the vaccine of AstraZeneca, stress the Professors of EKPA, state that the choice of many countries to recommend that the second dose of the vaccine be given less than 12 weeks after the first dose is correct, in order to shorten the time until maximum production of neutralising antibodies is reached. These countries include Greece, which proposes that the second dose of the vaccine should be administered in AstraZeneca between 8 and 12 weeks after the first dose, as well as the United Kingdom giving the second dose to vulnerable groups 8 weeks after the first dose, instead of the 12 weeks that was its usual policy until a week ago.