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Waning immunity six months after BioNTech/Pfizer COVID-19 vaccination among nursing home residents in Zagreb, Croatia

Kolarić, Branko; Ambriović Ristov, Andreja; Tabain, Irena; Vilibić-Čavlek, Tatjana (2021) Waning immunity six months after BioNTech/Pfizer COVID-19 vaccination among nursing home residents in Zagreb, Croatia. Croatian Medical Journal, 62 (6). pp. 630-633. ISSN 0353-9504

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Aim: To assess the humoral immunity to COVID-19 in nursing home residents six months after vaccination. Methods: This seroepidemiological research enrolled 118 residents of one nursing home in Zagreb. All participants received two doses of BioNTech/Pfizer COVID-19 and had no previously detected SARS-CoV-2 infection. The samples were tested for the presence of neutralizing antibodies using a virus neutralization test. A SARS-CoV-2 strain isolated in Vero E6 cells from a Croatian COVID-19 patient was used as a stock virus. Neutralizing antibody titer was defined as the reciprocal of the highest serum dilution that showed at least 50% neutralization. Neutralizing antibody titer ≥8 was considered positive. Results: Sixty-four (54%) participants had a positive neutralizing antibody titer, 27 (23%) had a low positive titer (titer 8), and 27 (23%) had a negative titer. Women had a significantly higher median titer than men (16 [interquartile range, IQR 24] vs 8 [IQR 12], Mann-Whitney U = 1033, P = 0.003). Age was negatively but not significantly correlated with neutralizing antibody titer (Spearman’s rho -0.132, P = 0.155). Conclusion: Almost half of the participants (46%) had a negative or low positive titer six months after having been fully vaccinated. This study suggests that humoral immunity among nursing home residents considerably wanes six months after BioNTech/Pfizer COVID-19 vaccination. Our results could contribute to the discussion about the need for a booster dose.

Item Type: Article
Uncontrolled Keywords: COVID-19; BioNTech/Pfizer; vaccination; nursing home
Subjects: BIOMEDICINE AND HEALTHCARE > Public Health and Health Care
Divisions: Division of Molecular Biology
Depositing User: Ana Zečević
Date Deposited: 27 Mar 2024 11:30
DOI: 10.3325/cmj.2021.62.630

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