Antibody levels following vaccination against SARS-CoV-2 during an 11-month follow-up.

Aims: The primary aim of our monitoring was to determine the duration of persistence of antibody levels following administration of the Comirnaty (Pfizer/BioNTech) mRNA vaccine. The second aim was to analyse the effect of selected factors on the level of antibodies.

Methods: The study cohort consisted of 250 employees of the Medirex JSC laboratories. For the quantitative determination of specific IgG anti-S1 and anti-S2 antibodies to SARS-CoV-2, chemiluminescence immunoassay was used. Twenty-nine subjects were excluded from the analysis due to extreme values of antibody levels in individual measurements. The effect of gender, age, BMI, comorbidity, and adverse reactions after vaccination with the Comirnaty (Pfizer/BioNTech) mRNA vaccine on antibody levels was analysed. Comparisons were made for five samples collected from two weeks after the 1st dose to 36 weeks after the 2nd dose of the mRNA vaccine. After the fifth sampling, the cohort was divided into two groups. Group 1 received the 3rd dose, and Group 2 were controls. We performed the last (sixth) sample collection two weeks after booster administration in Group 1and 11 months after the 2nd dose of the vaccine in controls. Between months 8 and 10 after the 2nd dose, we performed a cellular immunity test.

Results: Altogether 99.6% of the participants had a positive antibody level at week 36. Antibodies were still present in controls at month 11 after the 2nd dose. Significantly higher antibody levels were found in females, younger subjects, and those with selected adverse reactions. Reactive specific T lymphocytes were present in 65.6% of the subjects between weeks 36 and 44.

Conslusion: The antibody response decreased with the time since the 2nd dose but was still present in the control group at week 48. The effect of booster on antibody levels was clearly demonstrated. We have not confirmed an association of cellular immunity with the level of antibodies or with the antibodies present.