A document by Mary Anissa Sinnathamby. Click on the document to view its contents.

Introduction: The aim of the study was to assess the seroprevalence of SARS-CoV-2 in the Republika Srpska, Bosnia and Herzegovina, after five waves of COVID-19 and one year after introduction of vaccination to better understand the true extent of the COVID-19 pandemic and role of vaccination in achieving herd immunity. Methods: The population-based study was conducted from December 2021 to February 2022 in a group of 4,463 individuals from the Republika Srpska. Total anti-SARS-CoV-2 antibodies were determined in serum specimens using the Wantai total antibody ELISA assay and Kantaro Quantitative IgG assays. Results: The overall cumulative seroprevalence was 94.6%. Of all participants, 61.3% were vaccinated against COVID-19. Significantly higher seroprevalence rates were observed among vaccinated participants. Among various professions, the highest seroprevalence was found in the service industry (98.1%), education (98.0%) and healthcare (96.9%). This study found that 2.2% of vaccinated participants, and 3.6% of individuals with SARS-CoV-2 positivity during 2021, had no detectable IgG antibodies. Both seroprevalence and antibody titres were significantly higher in people with hybrid immunity. Conclusion: Our findings reveal a 2,3-fold increase in seroprevalence of SARS-CoV-2 antibodies due to infection and vaccination, comparing to the first study performed one year earlier. This study provides better understanding of the SARS-CoV-2 transmission and highlights the important role of the vaccination in achieving the population immunity. Periodically conducted population-based seroprevalence studies are important for assessment of surveillance system performance and public compliance with vaccination policies. Keywords: COVID-19, SARS-CoV-2 antibodies, seroprevalence, population-based study, Bosnia and Herzegovina, UNITY, SEROPREV.

Background: The emergence of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in early 2020 and subsequent implementation of public health and social measures (PHSM) disrupted the epidemiology of respiratory viruses. This work describes the epidemiology of RSV observed during two winter seasons (weeks 40 to 20) and inter-seasonal periods (weeks 21 to 39) during the pandemic between October 2020 and September 2022. Methods: Using data submitted to The European Surveillance System (TESSy) by countries or territories in the World health Organization (WHO) European Region between weeks 40/2020 and 39/2022, we aggregated country-specific weekly RSV counts of sentinel, non-sentinel and Severe Acute Respiratory Infection (SARI) surveillance specimens and calculated percentage positivity. Results for both 2020/21 and 2021/22 seasons and inter-seasons were compared to pre-pandemic 2016/17 to 2019/20 seasons and inter-seasons. Results: Although more specimens were tested than in pre-COVID-19 pandemic seasons, very few RSV detections were reported during the 2020/21 season in all surveillance systems. During the 2021 inter-season, a gradual increase in detections was observed in all systems. In 2021/22, all systems saw early peaks of RSV infection, and during the 2022 inter-seasonal period, patterns of detections were closer to those seen before the COVID-19 pandemic. Conclusion: RSV surveillance continued throughout the COVID-19 pandemic, with an initial reduction in transmission, followed by very high and out-of-season RSV circulation (summer 2021) and then an early start of the 2021/22 season. RSV circulation during the 2022/23 season had not yet normalised.

Background Sarajevo Canton in the Federation of Bosnia and Herzegovina has recorded several waves of high SARS-CoV-2 transmission and has struggled to reach adequate vaccination coverage. We describe the evolution of infection- and vaccine-induced SARS-CoV-2 antibody response and persistence. Methods We conducted repeated cross-sectional analyses of blood donors aged 18-65 years in Sarajevo Canton in November-December 2020 and 2021. We analyzed serum samples for anti-nucleocapsid (anti-N) and anti-spike (anti-S) antibodies. To assess immune durability, we conducted longitudinal analyses of seropositive participants at 6 and 12 months. Results 1015 participants were included in Phase 1 (November-December 2020), and 1152 in Phase 2 (November-December 2021). Seroprevalence increased significantly from 19.2% (95% CI: 17.2-21.4%) in Phase 1 to 91.6% (95% CI: 89.8-93.1%) in Phase 2. Anti-S IgG titers were significantly higher among vaccinated (58.5%) than unvaccinated infected participants across vaccine products (p<0.001), though highest among those who received an mRNA vaccine. At 6 months, 78/82 (95.1%) participants maintained anti-spike seropositivity; at 12 months, 58/58 (100.0%) participants were seropositive and 33 (56.9%) had completed the primary vaccine series within 6 months. Among 11 unvaccinated participants who were not reinfected at 12 months, anti-S IgG declined from median 770.1 (IQR 615.0-1321.7) to 290.8 (IQR 175.7-400.3). Anti-N IgG antibodies waned earlier; from 35.4% seropositive at 6 months to 24.1% at 12 months. Conclusions SARS-CoV-2 seroprevalence increased significantly over 12 months from end of 2020 to end of 2021. Although individuals with previous infection may have residual protection, COVID-19 vaccination is vital to strengthening population immunity.

Background Healthcare workers (HCWs) have suffered considerable morbidity and mortality during the COVID-19 pandemic. Few studies have evaluated Coronavac vaccine effectiveness (VE), particularly in eastern Europe, where the vaccine has been widely used. Methods We conducted a prospective cohort study among HCWs in seven hospitals in Baku, Azerbaijan between May 17 to December 1, 2021, to evaluate primary series (two-dose) CoronaVac VE against symptomatic SARS-CoV-2 infection. Participants completed weekly symptom questionnaires, provided nasal swabs for SARS-CoV-2 RT-PCR testing when symptomatic, and provided serology samples at enrolment that were tested for anti-spike and anti-nucleocapsid antibodies. We estimated VE as (1 – hazard ratio)*100 using a Cox proportional hazards model with vaccination status as a time-varying covariate. Results We enrolled 1582 HCWs. At enrolment, 1040 (66%) had received two doses of CoronaVac; 421 (27%) were unvaccinated. During the study period, 72 PCR-positive SARS-CoV-2 infections occurred; 36/39 (92%) sequenced samples were classified as delta variant. The adjusted primary series VE against COVID-19 illness was 29% (95% CI:-51%;67%). For the delta-predominant period, adjusted primary series VE was 19% (95% CI:-81%;64%). For the entire analysis period, adjusted primary series VE was 39% (95% CI:-40%;73%) for HCW vaccinated within 14–149 days, and 19% (95%CI:-81;63) for those vaccinated ≥150 days. Conclusions During a delta-predominant period in Azerbaijan, point estimates suggest that primary series CoronaVac protected nearly 1 in 3 HCWs against COVID-19, but this finding was not statistically significant. Our findings underscore the need to consider booster doses in individuals who have received primary series CoronaVac.

We evaluated uptake and factors associated with COVID-19 vaccination among health workers (HWs) in Azerbaijan. Among 1,575 HWs, 73% had received at least one dose and 67% received two doses; all received CoronaVac. Factors associated with vaccination uptake included no previous COVID-19 infection, older age, belief in the vaccine’s safety, previous vaccination for influenza, having patient-facing roles, and good or excellent health by self-assessment. These findings could inform strategies to increase vaccination uptake as the campaign continues.

Respiratory Syncytial Virus (RSV) is a common seasonal respiratory virus and an important cause of illness among infants, but the burden of RSV disease is not well described among the older population. The objective of this study was to estimate the age-specific incidence of hospital admission among over 65s due to respiratory illnesses attributable to RSV in England to inform optimal vaccine and therapeutic interventions. We used linear multiple regression to examine the effect of changes in weekly counts of respiratory pathogens on the weekly counts of respiratory hospital admissions. The study population was all patients aged 65 years or over admitted to English hospitals between 2nd August 2010 and 30th July 2017. RSV was estimated to account for a seasonal annual average of 71 (95% CI 52-90) respiratory admissions per 100,000 in adults age 65-74 and 251 (95% CI 186-316) admissions per 100,000 adults age 75+. Pneumococcus was the pathogen responsible for highest annual average respiratory admission with 448 (95% CI 310-587) admissions per 100,000 adults age 65-74 and 1010 (95%CI 527-1493) admissions per 100,000 adults aged 75+. This study shows that RSV continues to exert a significant burden of disease among older adults in England. These findings will support development of policy for the use of RSV therapeutics and vaccines in this age group.