BackgroundWe aimed to detect SARS-CoV-2 serum antibodies in the general population of the Netherlands and identify risk factors for seropositivity amidst the first COVID-19 epidemic wave.MethodsParticipants (n=3207, aged 2–90 years), enrolled from a previously established nationwide serosurveillance study, provided a self-collected fingerstick blood sample and completed a questionnaire (median inclusion date 3 April 2020). IgG antibodies targeted against the spike S1-protein of SARS-CoV-2 were quantified using a validated multiplex-immunoassay. Seroprevalence was estimated controlling for survey design, individual pre-pandemic concentration, and test performance. Random-effects logistic regression identified risk factors for seropositivity.ResultsOverall seroprevalence in the Netherlands was 2.8% (95% CI 2.1 to 3.7), with no differences between sexes or ethnic background, and regionally ranging between 1.3 and 4.0%. Estimates were highest among 18–39 year-olds (4.9%), and lowest in children 2–17 years (1.7%). Multivariable analysis revealed that persons taking immunosuppressants and those from the Orthodox-Reformed Protestant community had over four times higher odds of being seropositive compared to others. Anosmia/ageusia was the most discriminative symptom between seropositive (53%) and seronegative persons (4%, p<0.0001). Antibody concentrations in seropositive persons were significantly higher in those with fever or dyspnoea in contrast to those without (p=0.01 and p=0.04, respectively).ConclusionsIn the midst of the first epidemic wave, 2.8% of the Dutch population was estimated to be infected with SARS-CoV-2, that is, 30 times higher than reported. This study identified independent groups with increased odds for seropositivity that may require specific surveillance measures to guide future protective interventions internationally, including vaccination once available.

Background The COVID-19 pandemic necessitates a better understanding of the kinetics of antibody production induced by infection with SARS-CoV-2. We aimed to develop a high throughput multiplex assay to detect antibodies to SARS-CoV-2 to assess immunity to the virus in the general population. Methods Spike protein subunits S1 and RBD, and Nucleoprotein were coupled to distinct microspheres. Sera collected before the emergence of SARS-CoV-2 (N=224), and of non-SARS-CoV-2 influenza-like illness (N=184), and laboratory-confirmed cases of SARS-CoV-2 infection (N=115) with various severity of COVID-19 were tested for SARS-CoV-2-specific concentrations of IgG. Results Our assay discriminated SARS-CoV-2-induced antibodies and those induced by other viruses. The assay obtained a specificity between 95.1 and 99.0% with a sensitivity ranging from 83.6-95.7%. By merging the test results for all 3 antigens a specificity of 100% was achieved with a sensitivity of at least 90%. Hospitalized COVID-19 patients developed higher IgG concentrations and the rate of IgG production increased faster compared to non-hospitalized cases. Conclusions The bead-based serological assay for quantitation of SARS-CoV-2-specific antibodies proved to be robust and can be conducted in many laboratories. Finally, we demonstrated that testing of antibodies against different antigens increases sensitivity and specificity compared to single antigen-specific IgG determination.

NCT00815282.

Background Assessing the duration of immunity following infection with SARS-CoV-2 is a first priority to gauge the degree of protection following infection. Such knowledge is lacking especially in the general population. Here, we studied changes in Immunoglobulin (Ig) isotype seropositivity and IgG binding strength of SARS-CoV-2-specific serum antibodies up to 7 months following onset of symptoms in a nationwide sample. Methods Participants from a prospective representative serological study in the Netherlands were included based on IgG seroconversion to the Spike S1 protein of SARS-CoV-2 (N=353), with up to three consecutive serum samples per seroconverted participant (N=738). IgM, IgA and IgG antibody concentrations to S1, and increase in IgG avidity in relation to time since onset of disease symptoms, were determined. Results While SARS-CoV-2-specific IgM and IgA antibodies declined rapidly after the first month post onset of disease, specific IgG was still present in 92% (95% confidence interval, CI, 89-95) of the participants after 7 months. The estimated 2-fold decrease of IgG antibodies was 158 days (95% CI 136-189). Concentrations sustained better in persons reporting significant symptoms compared to asymptomatic persons or those with mild upper respiratory complaints only. Similarly, avidity of IgG antibodies for symptomatic persons showed a steeper increase over time compared with persons with mild or no symptoms (p=0.022). Conclusion SARS-CoV-2-specific IgG antibodies persist and show increasing avidity over time, indicative of underlying immune maturation. These data support development of immune memory against SARS-CoV-2 providing insight into protection of the general unvaccinated part of the population.

BackgroundIn 2002 a Meningococcal serogroup C (MenC) conjugate vaccine, with tetanus toxoid as carrier protein, was introduced in the Netherlands as a single-dose at 14 months of age. A catch-up campaign was performed targeting all individuals aged 14 months to 18 years. We determined the MenC-specific immunity before and after introduction of the MenC conjugate (MenCC) vaccine.Methods and FindingsTwo cross-sectional population-based serum banks, collected in 1995/1996 (n = 8539) and in 2006/2007 (n = 6386), were used for this study. The main outcome measurements were the levels of MenC polysaccharide(PS)-specific IgG and serum bactericidal antibodies (SBA) after routine immunization, 4–5 years after catch-up immunization or by natural immunity. There was an increasing persistence of PS-specific IgG and SBA with age in the catch-up immunized cohorts 4–5 years after their MenCC immunization (MenC PS-specific IgG, 0.25 µg/ml (95%CI: 0.19–0.31 µg/ml) at age 6 years, gradually increasing to 2.34 µg/ml,(95%CI: 1.70–3.32 µg/ml) at age 21–22 years). A comparable pattern was found for antibodies against the carrier protein in children immunized above 9 years of age. In case of vaccination before the age of 5 years, PS-specific IgG was rapidly lost. For all age-cohorts together, SBA seroprevalence (≥8) increased from 19.7% to 43.0% in the pre- and post-MenC introduction eras, respectively. In non-immunized adults the SBA seroprevalence was not significantly different between the pre- and post-MenC introduction periods, whereas PS-specific IgG was significantly lower in the post-MenC vaccination (GMT, age ≥25 years, 0.10 µg/ml) era compared to the pre-vaccination (GMT, age ≥25 years, 0.43 µg/ml) era.ConclusionMenCC vaccination administered above 5 years of age induced high IgG levels compared to natural exposure, increasing with age. In children below 14 months of age and non-immunized cohorts lower IgG levels were observed compared to the pre-vaccination era, whereas functional levels remained similar in adults. Whether the lower IgG poses individuals at increased risk for MenC disease should be carefully monitored. Large-scale introduction of a MenCC vaccine has led to improved protection in adolescents, but in infants a single-dose schedule may not provide sufficient protection on the long-term and therefore a booster-dose early in adolescence should be considered.

ObjectivesIn order to assess HPV-specific IgG characteristics, we evaluated multiple aspects of the humoral antibody response that will provide insight in the HPV humoral immune response induced by HPV infection and vaccination.MethodsCross-reactivity of HPV-specific antibodies induced by infection or vaccination was assessed with VLP16 or 18 inhibition using a VLP-based multiplex immunoassay (MIA) for HPV16, 18, 31, 33, 45, 52 and 58. HPV16/18 specific IgG1-4 subclasses and avidity were determined with the VLP-MIA in sera after HPV infection and after vaccination. Neutralizing antibodies were determined in a small subset of single-seropositive and multi-seropositive naturally derived antibodies.ResultsNaturally derived antibodies from single-positive sera were highly genotype-specific as homologue VLP-inhibition percentages varied between 78-94%. In multi-positive sera, cross-reactive antibodies were observed both within and between α7 and α9 species. After vaccination, cross-reactive antibodies were mainly species-specific. Avidity of vaccine-derived HPV-specific antibodies was 3 times higher than that of antibodies induced by HPV infection (p<0.0001). IgG1 and IgG3 were found to be the predominant subclasses observed after HPV infection and vaccination. In the small subset tested, the number of single-positive sera with neutralizing capacity was higher than of multi-positive sera.ConclusionNaturally derived HPV-specific antibodies from single-positive samples showed different characteristics in terms of cross-reactivity and neutralizing capacity compared with antibodies from multi-positive sera. Post-vaccination, HPV antibody avidity was approximately 3 times higher than antibody avidity induced by HPV infection. Therefore, antibody avidity might be a potential surrogate of protection.

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The close genetic relationship of human and animal strains of norovirus has raised the possibility of transmission of noroviruses from animals to humans and may explain the emergence of certain norovirus strains. To assess if exposure to bovine noroviruses (NoV) might result in infection in humans, an enzyme immunoassay (EIA) was designed and validated in order to detect antibodies against bovine norovirus. This and two other EIAs were used to test sera from 210 veterinarians and 630 matched population controls for IgG and IgA antibodies to recombinant capsid protein of bovine NoV (rBoV), Norwalk virus (rNV), and Lordsdale virus (rLDV). Of 840 participants, IgG reactivity to rBoV was found in 185 (22%), to rNV in 638 (76%) and to rLDV in 760 (90%). IgG reactivity to rBoV was more common in veterinarians (58/210: 28%) than in controls (127/630: 20% [P = 0.03]). IgA reactivity to rBoV was similar in both veterinarians and controls. Cross-reactivity of IgA and IgG antibodies to rBoV and rNV was seen, but 26% of all specimens positive rBoV antibodies showed high IgG reactivity to rBoV but low reactivity to rNV, suggesting a specific response to bovine antigen. No evidence of overall cross-reactivity of antibodies to rBoV and rLDV was seen. Among veterinarians, youth spent on farm (Odds Ratio [OR] = 1.8) and membership of the bovine practitioners' society (OR = 2.7) were significantly associated with IgG seroreactivity to rBoV. These data indicate that bovine strains of NoV may infect humans though less frequently than human strains.