Nationwide SARS-CoV-2 Seroprevalence Trends in the Netherlands in the Variant of Concern Era, 2021-2022: an Ongoing Prospective Cohort Study (preprint)

BackgroundRepeated population-based SARS-CoV-2 serosurveillance is key in complementing other surveillance tools. AimAssessing trends in infection- and/or vaccine-induced immunity, including breakthrough infections, among (sub)groups and regions in the Dutch population during the Variant of Concern (VOC)-era whilst varying levels of stringency, to evaluate population immunity dynamics and inform future pandemic response planning. MethodsIn this prospective population-based cohort, randomly-selected participants (n=9,985) aged 1-92 years (recruited since early-2020) donated home-collected fingerstick blood samples at six timepoints in 2021-2022, covering waves dominated by Alpha, Delta, and Omicron (BA.1, BA.2, BA.5). IgG antibody assessments against Spike-S1 and Nucleoprotein were combined with vaccination- and testing data to estimate infection-induced (inf) and total (infection- and vaccination-induced) seroprevalence. ResultsIn 2021, nationwide inf-seroprevalence rose modestly from 12% since Alpha to 26% amidst Delta, while total seroprevalence increased rapidly to nearly 90%, particularly fast in vulnerable groups (i.e., elderly and those with comorbidities). Highest infection rates were noticeable in adolescents and young adults, low/middle educated elderly, non-Western, contact professions (other than healthcare), and low-vaccination coverage regions. In 2022, following Omicron emergence, inf-seroprevalence elevated sharply to 62% and further to 86%, with frequent breakthrough infections and reduction of seroprevalence dissimilarities between most groups. Whereas >90% of <60-year-olds had been infected, 30% of vaccinated vulnerable individuals had not acquired hybrid immunity. ConclusionAlthough total SARS-CoV-2 seroprevalence had increased rapidly, infection rates were unequally distributed within the Dutch population. Ongoing tailored vaccination efforts and (sero-)monitoring of vulnerable groups remain important given their lowest rate of hybrid immunity and highest susceptibility to severe disease.

Reduced antibody acquisition with increasing age following vaccination with BNT162b2: results from a large study performed in the general population aged 12 to 92 years (preprint)

Vaccine-induced protection of the population against severe COVID-19, hospitalization and death is of utmost importance, especially in the elderly. However, limited data are available on humoral immune responses following COVID-19 vaccination in the general population across a broad age range. We performed an integrated analysis of the effect of age, sex and prior SARS-CoV-2 infection on Spike S1-specific (S1) IgG concentrations up to three months post BNT162b2 vaccination. 1,735 persons, eligible for COVID-19 vaccination through the national program, were recruited from the general population (12 to 92 years old). Sixty percent were female and the median vaccination interval was 35 days (interquartile range, IQR: 35-35). All participants had seroconverted to S1 one month after two doses of vaccine. S1 IgG was higher in participants with a history of SARS-CoV-2 infection (median: 4,535 BAU/ml, IQR: 2,341-7,205) compared to infection-naive persons (1,842 BAU/ml, 1,019-3,116) after two doses, p<0.001. In infection-naive persons, linear mixed effects regression showed a strong negative association between age and S1 IgG one month after the first vaccination (p<0.001) across the entire age range. The association was still present after the second vaccination, but less pronounced. Females had higher S1 IgG than males after both the first and second vaccination (p<0.001); although this difference was lower after the second dose. In persons with an infection history, age nor sex was associated with peak S1 IgG. As IgG decreased with age and time since vaccination, older persons may become at risk of infection, especially with escape variants such as Omicron.

SARS-CoV-2 Spike S1-specific IgG kinetic profiles following mRNA- versus vector-based vaccination in the general Dutch population (preprint)

mRNA- and vector-based vaccines are used at a large scale to prevent COVID-19. We compared Spike S1-specific (S1) IgG antibodies after vaccination with mRNA-based (Comirnaty, Spikevax) or vector-based (Janssen, Vaxzevria) vaccines, using samples from a Dutch nationwide cohort. mRNA vaccines induced faster inclines and higher S1 antibodies compared to vector-based vaccines in adults 18-64 years old (n=2,412). For all vaccines, one dose resulted in boosting of S1 antibodies in adults with a history of SARS-CoV-2 infection. For Comirnaty, two to four months following the second dose (n=196), S1 antibodies in adults aged 18-64 years old (436 BAU/mL, interquartile range: 328-891) were less variable and median concentrations higher compared to those in persons [≥]80 years old (366, 177-743), but differences were not statistically significant (p>0.100). Nearly all participants seroconverted following COVID-19 vaccination, including the aging population. These data confirm results from controlled vaccine trials in a general population, including vulnerable groups.

Seropositivity to Nucleoprotein to detect SARS-CoV-2 infections: a tool to detect breakthrough infections after COVID-19 vaccination (preprint)

BackgroundWith COVID-19 vaccine roll-out ongoing in many countries globally, monitoring of breakthrough infections is of great importance. Antibodies persist in the blood after a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Since COVID-19 vaccines induce immune response to the Spike protein of the virus, which is the main serosurveillance target to date, alternative targets should be explored to distinguish infection from vaccination. MethodsMultiplex immunoassay data from 1,513 SARS-CoV-2 RT-qPCR-tested individuals (352 positive and 1,161 negative) with a primary infection and no vaccination history were used to determine the accuracy of Nucleoprotein-specific immunoglobulin G (IgG) in detecting past SARS-CoV-2 infection. We also described Spike S1 and Nucleoprotein-specific IgG responses in 230 COVID-19 vaccinated individuals (Pfizer/BioNTech). ResultsThe sensitivity of Nucleoprotein seropositivity was 85% (95% confidence interval: 80-90%) for mild COVID-19 in the first two months following symptom onset. Sensitivity was lower in asymptomatic individuals (67%, 50-81%). Participants who had experienced a SARS-CoV-2 infection up to 11 months preceding vaccination, as assessed by Spike S1 seropositivity or RT-qPCR, produced 2.7-fold higher median levels of IgG to Spike S1 [≥]14 days after the first dose as compared to those unexposed to SARS-CoV-2 at [≥]7 days after the second dose (p=0.011). Nucleoprotein-specific IgG concentrations were not affected by vaccination in naive participants. ConclusionsSerological responses to Nucleoprotein may prove helpful in identifying SARS-CoV-2 infections after vaccination. Furthermore, it can help interpret IgG to Spike S1 after COVID-19 vaccination as particularly high responses shortly after vaccination could be explained by prior exposure history.

Tolerability, safety and immunogenicity of intradermal delivery of a fractional dose mRNA -1273 SARS-CoV-2 vaccine in healthy adults as a dose sparing strategy (preprint)

Background There is an urgent need for fair and equitable access to safe and effective vaccines to end the COVID-19 pandemic. Shortages in reagents and vaccines are a major challenge, as well as limited knowledge on dose response relationship with mRNA COVID-19 vaccines. We explored intradermal fractional dose administration of a mRNA SARS-CoV-2/COVID-19 vaccine as a potential dose-sparing strategy. Methods We conducted a proof-of-concept, dose-escalation, open-label, randomised-controlled vaccine trial (IDSCOVA) in healthy adults aged 18-30 years. To test initial safety, ten participants received 10 g mRNA-1273 vaccine through intradermal injection at day 1 and 29. Following a favourable safety review, thirty participants were 1:1 randomised to receive 20 g mRNA-1273 either intradermally or intramuscularly. The primary endpoint was tolerability and safety. The secondary endpoint was seroconversion and specific IgG concentration against SARS-CoV-2 spike S1 and Receptor Binding Domain (RBD) after the second dose at day 43. We compared results to two historical cohorts of non-hospitalised COVID-19 patients and vaccinated individuals. Findings Thirty-eight of forty included participants (median age 25 years) completed the study. There were no serious adverse events. Self-reported local adverse reactions after intradermal delivery were mild, both in the 10 g and the 20 g group. In the higher dose group, systemic adverse reactions were more common, but still well tolerated. All 38 participants mounted substantially higher IgG-anti-S1 and IgG-anti-RBD concentrations at day 43 than COVID-19 controls. At day 43, anti-S1 (95% CI) was 1,696 (1,309-2,198) BAU/mL for the 10 g intradermal group, 1,406 (953.5-2,074) BAU/mL for the 20 g intramuscular group and 2,057 (1,421-2,975) BAU/mL for the 20 g intradermal group. Anti-S1 was 107.2 (63-182.2) BAU/mL for the convalescent plasma control group and 1,558 (547.8-4,433) BAU/mL for the individuals vaccinated with 100 g mRNA-1273. Interpretation Intradermal administration of 10 g and 20 g mRNA-1273 vaccine was well tolerated and safe, and resulted in a robust antibody response. Intradermal vaccination has the potential to be deployed for vaccine dose-sparing.

Tolerability, Safety and Immunogenicity of Intradermal Delivery of a Fractional Dose mRNA -1273 SARS-CoV-2 Vaccine in Healthy Adults as a Dose Sparing Strategy (preprint)

Background: There is an urgent need for fair and equitable access to safe and effective vaccines to end the COVID-19 pandemic. Shortages in reagents and vaccines are a major challenge, as well as limited knowledge on dose response relationship with mRNA COVID-19 vaccines. We explored intradermal fractional dose administration of a mRNA SARS-CoV-2/COVID-19 vaccine as a potential dose-sparing strategy. Methods: We conducted a proof-of-concept, dose-escalation, open-label, randomised-controlled vaccine trial (IDSCOVA) in healthy adults aged 18-30 years. To test initial safety, ten participants received 10 µg mRNA-1273 vaccine through intradermal injection at day 1 and 29. Following a favourable safety review, thirty participants were 1:1 randomised to receive 20 µg mRNA-1273 either intradermally or intramuscularly. The primary endpoint was tolerability and safety. The secondary endpoint was seroconversion and specific IgG concentration against SARS-CoV-2 spike S1 and Receptor Binding Domain (RBD) after the second dose at day 43. We compared results to two historical cohorts of non-hospitalised COVID-19 patients and vaccinated individuals. Findings: Thirty-eight of forty included participants (median age 25 years) completed the study. There were no serious adverse events. Self-reported local adverse reactions after intradermal delivery were mild, both in the 10 µg and the 20 µg group. In the higher dose group, systemic adverse reactions were more common , but still well tolerated. All 38 participants mounted substantially higher IgG-anti-S1 and IgG-anti-RBD concentrations at day 43 than COVID-19 controls. At day 43, anti-S1 (95% CI) was 1,696 (1,309-2,198) BAU/mL for the 10 µg intradermal group, 1,406 (953·5-2,074) BAU/mL for the 20 µg intramuscular group and 2,057 (1,421-2,975) BAU/mL for the 20 µg intradermal group. Anti-S1 was 107·2 (63-182·2) BAU/mL for the convalescent plasma control group and 1,558 (547·8-4,433) BAU/mL for the individuals vaccinated with 100 µg mRNA-1273.Interpretation: Intradermal administration of 10 µg and 20 µg mRNA-1273 vaccine was well tolerated and safe, and resulted in a robust antibody response. Intradermal vaccination has the potential to be deployed for vaccine dose-sparing.Clinical Trial Registration Details: registered in the Netherlands Trial Register (NTR) (https://www.trialregister.nl/trial/9275).Funding Information: The trial was supported by crowdfunding (Wake Up to Corona).Declaration of Interests: All authors declare no competing interests. Ethics Approval Statement: The trial was performed in accordance with the ethical principles of the Declaration of Helsinki and Good Clinical Practice guidelines developed by the International Harmonisation Task Force. The protocol was approved by the Medical Ethical Committee Leiden, Den Haag, Delft (NL 76702.058.21). All participants provided written informed consent. The vaccine manufacturer was not involved in this trial.

SARS-CoV-2-specific antibody detection for sero-epidemiology: a multiplex analysis approach accounting for accurate seroprevalence (preprint)

Background The COVID-19 pandemic demands detailed 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.