Decreasing neutralization antibody levels following vaccination against SARS-CoV-2 in the elderly: an observational study in Southern Moravia, Czech Republic.

INTRODUCTION: Understanding the immune response after SARS-CoV-2 vaccination is essential to control the COVID-19 pandemic. Recent studies indicate that vaccine-induced humoral immunity may not be long-lasting and is weaker in the elderly.

METHODOLOGY AND SAMPLE: At the turn of June and July 2021, 653 seniors (426 women and 197 men with a mean age of 74 years) were tested once for antibodies against SARS-Cov-2 in the South Moravian Region between 9 and 161 days after the second dose of vaccine (558 Pfizer -BioNTech, 28 Moderna, 36 AstraZeneca, 1 Johnson & Johnson). Samples of the whole capillary blood were tested in two point-of-care iCHROMA II immunofluorescence assays: (1) COVID-19 Ab against mix of SARS-CoV-2 nucleocapsid and spike proteins (IgM Ab, IgG Ab) and (2) COVID-19 nAb against S1-RBD protein (nAb). Results were analysed in relation to gender, age, vaccine type, and past COVID-19 disease.

RESULTS: Our results show high variability in the antibody response but indicate an overall relatively weak and decreasing antibody response in the first six months after vaccination. Only 58.4% (95% CI: 54.6-62.3) of subjects had virus neutralizing antibodies (nAb). The level of nAb decreased with time from vaccination - at post-vaccination months 4 and 5, nAb were only detected in 41.1% (95% CI: 30.9-51.3) and 15.4% (95% CI: 1.5-29.3) of subjects, respectively. Vaccinees in older age groups, those vaccinated with AstraZeneca, and naive individuals showed a lower antibody response.

CONCLUSION: The antibody response to SARS-CoV-2 vaccine in the elderly was relatively weak and decreased in the first six months after vaccination. Although humoral immunity is complex and cellular immune memory is a key element of the humoral response after exposure to the wild virus, our results suggest that vaccine-induced humoral immunity may not be long-lasting. The oldest koncenage groups who have not acquired natural SARS-CoV-2 infection are particularly at risk. This finding is relevant for adjusting vaccination strategies in selected population groups to include a booster dose. More research into the antibody response and the complex immune response after vaccination against SARS-CoV-2 over longer time is needed.