Seroprevalence of anti-SARS-CoV-2 IgG antibodies pre- and post-COVID-19 vaccination in staff members of Bandar … – BMC Infectious Diseases

We assessed the seroprevalence of anti-SARS-CoV-2 spike protein IgG antibodies among the staff members of a childrens hospital and found that pre-vaccination, seroprevalence was 8.8% in all staff members and 9.5% in HCWs. After receiving the first vaccine dose, seroprevalence increased to 9.3% in all staff members but remained unchanged in HCWs (9.5%). After the second vaccine dose, seroprevalence considerably increased to 50% in all staff members and 48.8% in HCWs.

Assaid et al. reported a seroprevalence of 65.9% by Euroimmun ELISA five months after the second dose of vector or inactivated virus vaccines in HCWs. The antibody response did not differ significantly between HCWs who received either vaccine type [8], which is consistent with our results, showing no relationship between vaccine type and seroprevalence by adjusted logistic regression analysis. The higher seroprevalence in Assaid et al.s study can be justified by demographic and anthropometric differences and history of prior COVID-19 infection as none of the HCWs in Assaid et al.s study had a history of COVID-19 infection [8]. A small group of our subjects were previously infected with COVID-19, but we found no association between such history and anti-SARS-CoV-2 IgG seroprevalence. Nonetheless, a single dose of the vaccine may be sufficient to induce an effective response in previously infected individuals, suggested by Gobbi et al. [9]

Interestingly, the seroprevalence of anti-SARS-CoV-2 after two doses of vector vaccines was 91.7% in HCWs of the study by Elangovan in India. They also observed a significant increase in antibody levels of HCWs who had a history of COVID-19 infection within six months prior to vaccination [10]. The much lower seroprevalence in our study might be due to almost one-third of subjects receiving inactivated virus vaccines, the interval between two doses of vaccines, as well as demographic differences and work settings. More importantly, the accuracy of measurements is always a matter of concern when evaluating laboratory parameters

Another explanation for the higher seroprevalence in Assaid et al.s study [8] can be the time of antibody assessment. We evaluated anti-SARS-CoV-2 antibodies at least two weeks after the second vaccine dose while their measurements were done five months after the second dose. The two-week interval was chosen in our study because according to previous investigations, individuals vaccinated at least 14 days before antibody measurements were presumed to be seronegative [11]. However, Costa et al. reported higher antibody values with shorter time lapse around two to eight weeks between vaccination and serology [12]

Another finding of the present study was the positive correlation of age with anti-SARS-CoV-2 IgG seroprevalence after the second dose of vaccination as every one-year increase in age increased the odds of positive anti-SARS-CoV-2 IgG by 6%. Yet, the oldest subject in our study was 60 years old. Contrary to our findings, by studying antibody responses in 212,102 individuals, Ward et al. showed a decrease in antibody response with age, but this reduction was most prominent at ages 75 years and above [13]. On the other hand, we found no association between sex and seroprevalence. Conversely, Costa et al. reported lower serological levels in males [12]. A lower antibody response to mRNA vaccines has been demonstrated in men compared to women in other studies [14, 15]. Of note, although vaccine type did not influence seroprevalence in our study, none of the subjects received mRNA vaccines

We found that a longer interval between the two doses of vaccines was associated with a lower seroprevalence of anti-SARS-CoV-2 IgG antibodies. On the contrary, it has been demonstrated that a three-month interval between the primary vaccine dose and the booster might result in a better immune response compared to a short dose interval, when vector vaccines were concerned [16]

In the current study, neither univariable nor multivariable binary logistic regression analysis showed an association between BMI and seroprevalence of anti-SARS-CoV-2 IgG antibodies after the second dose of vaccination. Obesity can negatively affect the immune system, and vaccine uptake may differ based on BMI. However, in line with our findings, the current COVID-19 trials have shown no difference between groups with normal and obese BMIs in terms of vaccine efficacy [17]. Similarly, no association between BMI and serological response has been reported in cohorts and cross-sectional studies [12, 18, 19]. Contrarily, Pellini et al. have reported that immunogenicity of SARS-CoV-2 vaccine may be impaired by obesity [20]. Consequently, it is necessary to conduct further studies to better understand whether the long-term effectiveness of COVID-19 vaccination depends on individuals BMI.

Understanding the immunological reaction that generates a protective immunization to SARS-CoV-2 is crucial [21]. In comparison to the membrane, envelope, and nucleocapsid proteins, antibody responses to the spike protein are considered to be the predominant focus of neutralizing activity during viral infection [22, 23]. However, it is important to note that only a proportion of anti-SARS-CoV-2 spike protein IgG antibodies have neutralizing capacity, and no neutralization assays were performed in the current study. Therefore, the seroprevalence of anti-SARS-CoV-2 spike protein IgG antibodies may not accurately reflect the neutralizing effects of vaccines. It has been demonstrated that declining levels of neutralizing antibodies are associated with an increased risk of symptomatic infection, although the relationship is less clear for severe infections [24]

The current investigation had some limitations. The association between seroprevalence and the number of vaccine doses could not be evaluated since only those staff members who received the second vaccine dose were tested again for anti-SARS-CoV-2 IgG. Moreover, although we took prior COVID-19 infection into account, it is not clear how long ago the infection occurred. This is important because IgG titer attenuates over time. Also, we did not assess neutralizing antibodies and cell-mediated immune responses

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Seroprevalence of anti-SARS-CoV-2 IgG antibodies pre- and post-COVID-19 vaccination in staff members of Bandar ... - BMC Infectious Diseases