Neutralizing immunity against coronaviruses in Tanzanian health care workers

Abstract

The ongoing vaccination efforts and exposure to endemic and emerging coronaviruses can shape the population's immunity against this group of viruses. In this study, we investigated neutralizing immunity against endemic and emerging coronaviruses in 200 Tanzanian frontline healthcare workers (HCWs). Despite low vaccination rates (19.5%), we found a high SARS-CoV-2 seroprevalence (94.0%), indicating high exposure in these HCWs. Next, we determined the neutralization capacity of antisera against human coronavirus NL63, and 229E, SARS-CoV-1, MERS-CoV and SARS-CoV-2 (including Omicron subvariants: BA.1, BQ.1.1 and XBB.1.5) using pseudovirus neutralization assay. We observed a broad range of neutralizing activity in HCWs, but no neutralization activity detected against MERS-CoV. We also observed a strong correlation between neutralizing antibody titers for SARS-CoV-2 and SARS-CoV-1, but not between other coronaviruses. Cross-neutralization titers against the newer Omicron subvariants, BQ.1.1 and XBB.1.5, was significantly reduced compared to BA.1 and BA.2 subvariants. On the other hand, the exposed vaccinated HCWs showed relatively higher median cross-neutralization titers against both the newer Omicron subvariants and SARS-CoV-1, but did not reach statistical significance. In summary, our findings suggest a broad range of neutralizing potency against coronaviruses in Tanzanian HCWs with detectable neutralizing immunity against SARS-CoV-1 resulting from SARS-CoV-2 exposure.

Figure 1

Neutralization capacity of plasma (n = 186) form HCWs against coronaviruses spikes pseudotyped viruses. (a) Neutralisation profile of plasma against SARS-CoV-2 wildtype, SARS-CoV-1, MERS-CoV, HCoV-229E, and HCoV-NL63. (b) Comparison of neutralization titers between SARS-CoV-2 exposed-vaccinated (indicated by solid circles symbols) and exposed-unvaccinated (open diamond symbols), and (c) between SARS-CoV-2 seropositive (circle symbols) and seronegative groups (triangle symbols). The horizontal dotted line indicates the lowest limit of dilution tested (1:40). Statistical significance was determined using the Mann–Whitney-U rank test and P value < 0.05 was considered significant, (d) Spearman's correlation between neutralization titers for coronaviruses and the total anti-SARS-CoV-2 RBD binding antibodies quantified by ELISA. WT wild-type, NT neutralization titer.

Figure 2

Cross-neutralization of HCWs' plasma against newer omicron subvariants. (a) Matched paired analysis comparing neutralization titers for HCWs' plasma (n = 68) against wild-type SARS-CoV-2 and Omicron subvariants. “a” median NT50, “b” percentage of samples with NT50 > 40. Statistical significance was determined using the Wilcoxon test (****: P < 0.0001). (b) Comparison of neutralization titers across Omicron subvariants between SARS-CoV-2-exposed-vaccinated and SARS-CoV-2-exposed-unvaccinated HCWs. Statistical significance was determined using the Mann–Whitney-U rank test. In (a,b), the horizontal dotted line indicates the lowest limit of dilution tested (1:40).