Tracking by the IGC in homes reveals a fall in antibodies against COVID-19 in the elderly 6 months after vaccination. Of 260 elderly people aged over 70, only two thirds had detectable antibodies.
The tracking carried out by the IGC (Gulbenkian Science Institute) in homes revealed that, of 260 elderly people aged over 70, who had been monitored from the first dose of the vaccine against SARS-CoV-2, only 63% showed the presence of detectable antibodies 6 months after taking the vaccine.
The trend of falling antibodies began to be noted 3 months after the second dose, in around 15% of participants. On the other hand, of the 160 employees monitored in the five homes, representative of a younger population, 98.1% still had antibodies.
The data obtained after 6 months in relation to the Pfizer/BioNTech vaccine, confirm that, as occurs with other vaccines, the drop in antibodies generated by the vaccination is faster in the older population.
In the first phase of tracking, the effectiveness of the vaccine was measured and the levels of antibodies prior to the first dose, three weeks later, at the time of the second dose and three weeks after that were analysed. It was found that, after the second dose, the vast majority of residents (94%) responded to the vaccine by producing high levels of antibodies.
During the second phase, the persistence of response was evaluated, with various samples being taken over time. In the last sample, around 6 months after the start of vaccination, 63% of residents still had detectable antibodies. These data reflect the importance of continuing to track the fall in antibodies over time, in particular in this age bracket.
For Carlos Penha-Gonçalves, IGC researcher and coordinator of the tracking, the data obtained are foreseeable. “We had already noted that the onset of the immune reaction to vaccination was slower in this population, with around 33% of care home residents showing the presence of antibodies after taking the first dose of the vaccine, while 84% of the employees had a positive response”.
Although the monitoring of this reaction may provide new data, it is expected that people who had an antibody response shortly after vaccination will have developed immunological memory, which will allow them to fight infection should they subsequently come into contact with the virus.
The serological tracking is being conducted over the course of one year in care homes in the county of Almeirim and in Armed Forces Social Service care homes, and form part of a programme to evaluate the effectiveness of the reaction to vaccines against COVID-19 that the IGC has been promoting since the beginning of vaccination in Portugal, in December 2020.
The tracking programme covers a total of 2,844 health care professionals, workers in education and people with specific diseases, to whom different vaccines were administered. Tracking is an essential tool for guaranteeing monitoring of the evaluation of vaccine reaction and obtaining data to support decision-making regarding potential revaccination and the vaccines to be used.
