Scientists from the United States found that three months after vaccination with Pfizer and Moderna drugs, the humoral – associated with antibodies – the immune response to COVID-19 decreases. The researchers' article was published in Scientific Reports.
Scientists from Northwestern University tested blood samples from 27 adults – 13 with a positive test for coronavirus and 14 healthy. Participants in the study donated blood three times: the first time two to three weeks after the first dose of the vaccine, the second time after the second dose, and the third time two months after it. The researchers assessed the level of antibodies in the blood and how effectively they over time block the binding of the coronavirus peplomer protein to the ACE2 receptors – the main mechanism for the entry of SARS-CoV-2 into the cell.
The level of antibodies in the blood of the participants dropped markedly over the three months. The median antibody suppression rate three weeks after the second dose was 98 percent, but it dropped 20 percent after three months. The humoral immune response in those who had been ill with COVID-19 was, as expected, higher. However, it was found that those who had the disease without symptoms, it was comparable to that of people who tested negative for COVID-19.
The humoral immune response to the new strains of coronavirus was lower – three weeks after the second dose of the vaccine, the level of peplomer protein blocking for the “gamma” strain was 70 percent, and for the “beta” strain – 67. After three months, these showed a decrease by 31 and by 27.5 percent, respectively.