Seroprevalence of four endemic human coronaviruses and, reactivity and neutralization capability against SARS-CoV-2 among children in the Philippines

Abstract

Four endemic human coronaviruses (HCoV), HCoV-229E, HCoV-NL63, HCoV-HKU1, and HCoV-OC43, are closely related to SARS-CoV-2. These coronaviruses are known to infect humans living in temperate areas, including children under 5 years old; however, the seroprevalence of four HCoVs among children in tropical areas, including the Philippines, remains unclear. This study aimed to assess the prevalence of antibodies against four HCoVs and to determine the reactivity and neutralization of these antibodies against SARS-CoV-2 among children in the Philippines. A total of 315 serum samples collected from 2015 to 2018, before the emergence of SARS-CoV-2, in Biliran island, Philippines, were tested for the presence of antibodies against four HCoVs and SARS-CoV-2 using recombinant spike ectodomain proteins by IgG-enzyme-linked immunosorbent assay (ELISA). Reactivity to and neutralization of SARS-CoV-2 were also investigated. The seroprevalence of the four HCoVs was 63.8% for HCoV-229E, 71.4% for HCoV-NL63, 76.5% for HCoV-HKU1, and 83.5% for HCoV-OC43 by ELISA. Age group analysis indicated that seropositivity to all HCoVs reached 80% by 2-3 years of age. While 69/315 (21.9%) of the samples showed reactive to SARS-CoV-2, almost no neutralization against SARS-CoV-2 was detected using neutralization assay. Reactivity of antibodies against SARS-CoV-2 spike protein obtained by ELISA may not correlate with neutralization capability.

Figure 1

Seroprevalence of four endemic HCoVs and SARS-CoV-2 among different age groups of children who were collected before the COVID-19 pandemic (2015–2018) in the Philippines. The bar chart represents the percentage of serum samples that were positive for HCoV-229E (blue), HCoV-NL63 (red), HCoV-HKU1 (green), HCoV-OC43 (purple), and SARS-CoV-2 (orange) in each age group. The number of samples per age group is indicated in brackets.

Figure 2

Anti-SARS-CoV-2 antibodies, assessed by ELISA, according to seroreactive to four HCoVs and age in children who were collected before the COVID-19 pandemic (2015–2018). Seroreactive of the sera to (a) HCoV-229E, (b) HCoV-NL63, (c) HCoV-HKU1, and (d) HCoV-OC43, assessed by ELISA against the respective spike proteins of the different viruses. (e) Anti-SARS-CoV-2 antibodies according to age (negative: n = 246; positive: n = 69). The Y axis represents the ratio to cut-off-value of each antigen, or age, compared with Mann–Whitney U tests. Horizontal lines indicate mean values.

Figure 3

Correlation analysis of the cut-off-value ratio to the four HCoVs and to SARS-CoV-2 in children who were collected before the COVID-19 pandemic (2015–2018). Positive correlations are symbolized by graded shades of red, and negative correlations are by graded shades of blue. The coefficient of determination (R²) for each pair of viruses are indicated.

Figure 4

Assessment by PRNT of the neutralizing effect of the SARS-CoV-2 reactive sera. Percentage of inhibition of SARS-CoV-2 infection by reactive sera determined by PRNT in comparison with vehicle control. For each serum, the dot plot shows the correlation between the anti-SARS-CoV-2 reactivity, assessed by ELISA, and the neutralization, assessed by PRNT. A sample from a SARS-CoV-2-infected individual was used as a positive control (PC). SARS-CoV-2 non-reactive samples (negative) are represented with blue circles (n = 5), SARS-CoV-2 reactive samples (positive) are represented with black circles (n = 69). Data are compared by Spearman’s rank correlation coefficient.