Annual risk of hepatitis E virus infection and seroreversion: Insights from a serological cohort in Sitakunda, Bangladesh

Hepatitis E virus (HEV) is a major cause of acute jaundice in South Asia. Gaps in our understanding of transmission are driven by non-specific symptoms and scarcity of diagnostics, impeding rational control strategies. In this context, serological data can provide important proxy measures of infection. We enrolled a population-representative serological cohort of 2,337 individuals in Sitakunda, Bangladesh. We estimated the annual risks of HEV infection and seroreversion both using serostatus changes between paired serum samples collected 9 months apart, and by fitting catalytic models to the age-stratified cross-sectional seroprevalence. At baseline, 15% (95 CI: 14-17%) of people were seropositive, with seroprevalence highest in the relatively urban south. During the study, 27 individuals seroreverted (annual seroreversion risk: 15%, 95 CI: 10-21%), and 38 seroconverted (annual infection risk: 3%, 95CI: 2-5%). Relying on cross-sectional seroprevalence data alone, and ignoring seroreversion, underestimated the annual infection risk five-fold (0.6%, 95 CrI: 0.5-0.6%). When we accounted for the observed seroreversion in a reversible catalytic model, infection risk was more consistent with measured seroincidence. Our results quantify HEV infection risk in Sitakunda and highlight the importance of accounting for seroreversion when estimating infection incidence from cross-sectional seroprevalence data.

Diminished neutralizing activity against the XBB1.5 strain in 55.9% of individuals post 6 months COVID-19 mRNA booster vaccination: insights from a pseudovirus assay on 1,353 participants in the Fukushima vaccination community survey, Japan

This study investigates the neutralizing activity against the XBB1.5 variant and the ancestral strain in a population post-bivalent vaccination using a pseudo virus assay validated with authentic virus assay. While bivalent booster vaccination and past infections enhanced neutralization against the XBB 1.5 strain, individuals with comorbidities showed reduced responses. The study suggests the need for continuous vaccine updates to address emerging SARS-CoV-2 variants and highlights the importance of monitoring real-world immune responses.

Lack of seroprotection against diphtheria in the Austrian population, in light of reported diphtheria cases in Europe, 2022

Following an increase in diphtheria cases in Europe since 2022, we retrospectively estimated the prevalence of seroprotection against diphtheria and tetanus in 10,247 Austrian residents (population: 8,978,929) voluntarily tested between 2018 and 2022. Lack of seroprotection against diphtheria was found in 36% compared with 4% against tetanus. The geometric mean antibody concentration against tetanus was 7.9-fold higher compared with that for diphtheria. Raising awareness of regular booster vaccinations against diphtheria in combination with tetanus and pertussis is urgently needed.

Susceptibility to hepatitis B virus infection in adults living in Spain

BACKGROUND

A protective hepatitis B virus (HBV) vaccine has been available for four decades. Universal HBV vaccination of infants is recommended by the WHO since the 1990s. Furthermore, HBV immunization is advised for all adults with high-risk behaviours and no seroprotection. However, HBV vaccine coverage remains globally suboptimal. The advent of new more efficacious trivalent HBV vaccines has renewed the interest in HBV vaccination. At present, the extent of current HBV susceptibility in adults remains unknown in Spain.

METHODS

HBV serological markers were assessed on a large and representative sample of adults in Spain, including blood donors and individuals belonging to high-risk groups. Serum HBsAg, anti-HBc and anti-HBs were tested in specimens collected during the last couple of years.

RESULTS

From 13 859 consecutive adults tested at seven cities across the Spanish geography, overall 166 (1.2%) had positive HBsAg. Past HBV infection was recognized in 14% and prior vaccine immunization in 24%. Unexpectedly, 37% of blood donors and 63% of persons belonging to high-risk groups had no serum HBV markers and therefore were potentially HBV susceptible.

CONCLUSION

Roughly 60% of adults living in Spain seem to be HBV susceptible. Waning immunity might be more common than expected. Hence, HBV serological testing should be performed at least once in all adults regardless of risk exposures. HBV vaccine full courses or boosters should be administered to all adults lacking serological evidence of HBV protection.

Characterizing Longitudinal Antibody Responses in Recovered Individuals Following COVID-19 Infection and Single-Dose Vaccination: A Prospective Cohort Study

BACKGROUND

Investigating antibody titers in individuals who have been both naturally infected with SARS-CoV-2 and vaccinated can provide insight into antibody dynamics and correlates of protection over time.

METHODS

Human coronavirus (HCoV) IgG antibodies were measured longitudinally in a prospective cohort of qPCR-confirmed, COVID-19 recovered individuals (k = 57) in British Columbia pre- and post-vaccination. SARS-CoV-2 and endemic HCoV antibodies were measured in serum collected between Nov. 2020 and Sept. 2021 (n = 341). Primary analysis used a linear mixed-effects model to understand the effect of single dose vaccination on antibody concentrations adjusting for biological sex, age, time from infection and vaccination. Secondary analysis investigated the cumulative incidence of high SARS-CoV-2 anti-spike IgG seroreactivity equal to or greater than 5.5 log10 AU/mL up to 105 days post-vaccination. No re-infections were detected in vaccinated participants, post-vaccination by qPCR performed on self-collected nasopharyngeal specimens.

RESULTS

Bivariate analysis (complete data for 42 participants, 270 samples over 472 days) found SARS-CoV-2 spike and RBD antibodies increased 14-56 days post-vaccination (p < 0.001) and vaccination prevented waning (regression coefficient, B = 1.66 [95%CI: 1.45-3.46]); while decline of nucleocapsid antibodies over time was observed (regression coefficient, B = -0.24 [95%CI: -1.2-(-0.12)]). A positive association was found between COVID-19 vaccination and endemic human β-coronavirus IgG titer 14-56 days post vaccination (OC43, p = 0.02 & HKU1, p = 0.02). On average, SARS-CoV-2 anti-spike IgG concentration increased in participants who received one vaccine dose by 2.06 log10 AU/mL (95%CI: 1.45-3.46) adjusting for age, biological sex, and time since infection. Cumulative incidence of high SARS-CoV-2 spike antibodies (>5.5 log10 AU/mL) was 83% greater in vaccinated compared to unvaccinated individuals.

CONCLUSIONS

Our study confirms that vaccination post-SARS-CoV-2 infection provides multiple benefits, such as increasing anti-spike IgG titers and preventing decay up to 85 days post-vaccination.

SARS-CoV-2 antibody persistence in COVID-19 convalescent plasma donors: Dependency on assay format and applicability to serosurveillance

BACKGROUND

Antibody response duration following severe acute respiratory syndrome coronavirus 2 infection tends to be variable and depends on severity of disease and method of detection.

STUDY DESIGN AND METHODS

COVID-19 convalescent plasma from 18 donors was collected longitudinally for a maximum of 63-129 days following resolution of symptoms. All the samples were initially screened by the Ortho total Ig test to confirm positivity and subsequently tested with seven additional direct sandwich or indirect binding assays (Ortho, Roche, Abbott, Broad Institute) directed against a variety of antigen targets (S1, receptor binding domain, and nucleocapsid [NC]), along with two neutralization assays (Broad Institute live virus PRNT and Vitalant Research Institute [VRI] Pseudovirus reporter viral particle neutralization [RVPN]).

RESULTS

The direct detection assays (Ortho total Ig total and Roche total Ig) showed increasing levels of antibodies over the time period, in contrast to the indirect IgG assays that showed a decline. Neutralization assays also demonstrated declining responses; the VRI RVPN pseudovirus had a greater rate of decline than the Broad PRNT live virus assay.

DISCUSSION

These data show that in addition to variable individual responses and associations with disease severity, the detection assay chosen contributes to the heterogeneous results in antibody stability over time. Depending on the scope of the research, one assay may be preferable over another. For serosurveillance studies, direct, double Ag-sandwich assays appear to be the best choice due to their stability; in particular, algorithms that include both S1- and NC-based assays can help reduce the rate of false-positivity and discriminate between natural infection and vaccine-derived seroreactivity.

Intensified antibody response elicited by boost suggests immune memory in individuals administered two doses of SARS-CoV-2 inactivated vaccine

Neutralizing antibodies in the subjects of an inactivated SARS-CoV-2 vaccine clinical trial showed a decreasing trend over months. An investigation studying the third immunization suggested that the waning of neutralizing antibodies in individuals administered two doses of inactivated vaccine does not mean the disappearance of immunity.