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

Abstract

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.

Unpacking the Implications of SARS-CoV-2 Breakthrough Infections on COVID-19 Vaccination Programs

“…A study close to this in Croatia tested the samples from BioNTech/Pfizer fully vaccinated nursing home residents with no history of COVID-19 infections for the presence of neutralizing antibodies using a vaccine neutralizing test. The findings demonstrated that almost half (46%) of the participants had a negative or low positive titer six months after being fully vaccinated, suggesting the humoral immunity waning [21]. The studies cited in our present discussion show waning immunity as a function of time from complete vaccination translating to time to reinfection.…”

How Does Vaccination against SARS-CoV-2 Affect Hospitalized Patients with COVID-19?

“…In our study, in no case did more than 6 months elapse between the date of the last vaccine dose and the date of hospital admission. On the other hand, it is necessary to maintain the level of epidemiological alertness for the early detection of new variants of the virus that could escape the protective immunity induced by the vaccine and thus modify the evolution of the pandemic [27,28].…”

Characterization of SARS-CoV-2 vaccine waning in Mexico

“…Health care workers –considered to be at higher risk– who received the two doses of the Pfizer vaccine developed protective antibodies that were maintained at detectable levels at least for 250 days after the second dose of the vaccine (Coppeta et al, 2022). Other studies that report reduction in humoral response for several vaccines include Berar-Yanay et al (2021); Kolaric et al (2021); Khoury et al (2021); Peled et al; Levin et al (2021)…”

“…Health care workers -considered to be at higher risk-who received the two doses of the Pfizer vaccine developed protective antibodies that were maintained at detectable levels at least for 250 days after the second dose of the vaccine (Coppeta et al, 2022). Other studies that report reduction in humoral response for several vaccines include Berar-Yanay et al (2021); Kolaric et al (2021); Khoury et al (2021); Peled et al; Levin et al (2021) The estimates of VE are in general relative risk measures, some function of attack ratios (Lin et al, 2022) measured usually through a cohort-study or a test-negative design (Fukushima & Hirota, 2017) and thus provide a comparison between relative risk of vaccinated and unvaccinated groups. Tartof et al (2021) argues that a reduction in vaccine effectiveness against SARS-CoV-2 infections over time is more likely to be due to waning immunity rather than the delta variant escaping vaccine protection.…”