Risk of Vaccine Breakthrough SARS-CoV-2 Infection and Associated Factors in Healthcare Workers of Trieste Teaching Hospitals (North-Eastern Italy)

Background: Healthcare workers (HCWs) are particularly exposed to biological risk, including SARS-CoV-2 infection. In order to contrast the current pandemic and alleviate the burden of the disease on the healthcare system, a mass vaccination campaign against COVID-19 has been launched worldwide. Aim To evaluate the impact of COVID-19 vaccination in HCWs exposed to SARS-CoV-2, to describe the clinical presentation of COVID-19 in infected HCWs, and to investigate clinical and occupational risk factors for breakthrough infection. Design: Retrospective cohort study. Methods: The cohort of HCWs of Trieste Hospitals were followed up from 1 March 2020, to 30 November 2021 (21 months). All HCWs were periodically screened for SARS-CoV-2 infection by real-time PCR (RT–PCR) analysis. Clinical data were obtained through routine medical surveillance records. Risk factors for SARS-CoV-2 infection were investigated by univariable as well as multivariable logistic regression analysis. Results: Among 4394 HCWs routinely screened for SARS-CoV-2 by PCR on nasopharyngeal swab, a total of 800 incident cases were identified during the entire study period (1 March 2020 to 30 November 2021). Five hundred and sixty-four cases occurred before, and 236 after the start of the vaccination campaign against COVID-19, of whom 155 received a complete vaccination scheme before SARS-CoV-2 infection. Breakthrough infection was featured by mild or no symptoms and was significantly associated with the male sex, BMI > 25, and diabetes mellitus. Some categories of HCWs (physicians and nurse aids/auxiliary personnel) were at a higher risk of breakthrough infection. Conclusions: Fully vaccinated HCWs were less likely to acquire symptomatic as well as asymptomatic SARS-CoV-2 infection. Risk factors for SARS-CoV-2 infection after a full COVID-19 vaccination scheme included the male gender, diabetes mellitus, and overweight. HCWs with higher exposure to COVID-19 patients were at higher risk of breakthrough infection.     

The effectiveness of primary series CoronaVac vaccine in preventing COVID-19 illness: A prospective cohort study among healthcare workers in Azerbaijan,May–November 2021

Background

Healthcare workers (HCWs) have suffered considerable morbidity and mortality during the COVID-19 pandemic. Few studies have evaluated the 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 and November 30, 2021, to evaluate primary series (two-dose) CoronaVac VE against symptomatic SARS-CoV-2 infection. Participants completed weekly symptom questionnaires, provided nasopharyngeal swabs for SARS-CoV-2 RT-PCR testing when symptomatic, and provided serology samples at enrollment 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 exposure, adjusting for hospital and previous SARS-CoV-2 infection status.

Results

We enrolled 1582 HCWs. At enrollment, 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 variants. Primary series VE against COVID-19 illness was 29% (95% CI: −51%; 67%) for the entire analysis period. For the Delta-only period (July 1–November 30, 2021), primary series VE was 19% (95% CI: −81%; 64%). For the entire analysis period, primary series VE was 39% (95% CI: −40%; 73%) for HCWs vaccinated within 14–149 days and 19% (95% CI: −81%; 63%) for those vaccinated ≥150 days.

Conclusions

During a period in Azerbaijan characterized by mostly Delta circulation, VE point estimates suggested that primary series CoronaVac protected nearly 1 in 3 HCWs against COVID-19, but 95% confidence intervals were wide, with lower bounds that crossed zero, reflecting the limited precision of our VE estimates. Our findings underscore the need to consider booster doses for individuals who have received the primary series of CoronaVac.     

COVID-19 vaccination hesitancy among health care workers,communication, and policy-making

BackgroundCoronavirus disease 2019 (COVID-19) vaccine hesitancy in health care workers (HCWs) contributes to personal and patient risk in contracting COVID-19. Reasons behind hesitancy and how best to improve vaccination rates in HCWs are not clear.MethodsWe adapted a survey using the Health Belief Model framework to evaluate HCW vaccine hesitancy and reasons for choosing for or against COVID-19 vaccination. The survey was sent to 3 large academic medical centers in the Chicagoland area between March and May 2021.ResultsWe received 1974 completed responses with 85% of HCWs receiving or anticipating receiving COVID-19 vaccination. Multivariable logistic regression found HCWs were less likely to receive COVID-19 vaccination if they were Black (OR 0.34, 95% CI 0.15-0.80), Republican (OR 0.54, 95% CI 0.31-0.91), or allergic to any vaccine component (OR 0.27, 95% CI 0.10-0.70) and more likely to receive if they believed people close to them thought it was important for them to receive the vaccine (OR 5.2, 95% CI 3-8).ConclusionsA sizable number of HCWs remain vaccine hesitant 1 year into the COVID-19 pandemic. As HCWs are positively influenced by colleagues who believe in COVID-19 vaccination, development of improved communication across HCW departments and roles may improve vaccination rates.     

COVID-19 vaccine uptake and hesitancy opinions from frontline health care and social care workers: Survey data from 37 countries

Background and aimsVaccine hesitancy is an ongoing major challenge. We aimed to assess the uptake and hesitancy of the COVID-19 vaccination.MethodsA short online survey was posted between April 12 to July 31, 2021 targeted at health and social care workers (HCWs) across the globe.Results275 from 37 countries responded. Most were hospital or primary care physicians or nurses, 59% women, aged 18–60 years, and 21% had chronic conditions with most prevalent being diabetes, hypertension, and asthma. We found that most HCWs (93%) had taken or willing to receive the COVID-19 vaccine. While 7% were vaccine hesitant (mainly women aged 30–39 years), respondents main concerns was the safety or potential side effects. Vaccine willing respondents raised concerns of unequal access to the COVID-19 vaccination in some countries, and highlighted that the only solution to overcoming COVID-19 infections was the vaccine booster doses given annually and free mass vaccination.ConclusionsThis study found that the majority of the frontline HCWs are willing to receive the COVID-19 vaccine. Further promotion of the COVID-19 vaccine would reassure and persuade HCWs to become vaccinated.     

Investigating COVID-19 Vaccine Impact on the Risk of Hospitalisation through the Analysis of National Surveillance Data Collected in Belgium

The national vaccination campaign against SARS-CoV-2 started in January 2021 in Belgium. In the present study, we aimed to use national hospitalisation surveillance data to investigate the recent evolution of vaccine impact on the risk of COVID-19 hospitalisation. We analysed aggregated data from 27,608 COVID-19 patients hospitalised between October 2021 and February 2022, stratified by age category and vaccination status. For each period, vaccination status, and age group, we estimated risk ratios (RR) corresponding to the ratio between the probability of being hospitalised following SARS-CoV-2 infection if belonging to the vaccinated population and the same probability if belonging to the unvaccinated population. In October 2021, a relatively high RR was estimated for vaccinated people > 75 years old, possibly reflecting waning immunity within this group, which was vaccinated early in 2021 and invited to receive the booster vaccination at that time. In January 2022, a RR increase was observed in all age categories coinciding with the dominance of the Omicron variant. Despite the absence of control for factors like comorbidities, previous infections, or time since the last administered vaccine, we showed that such real-time aggregated data make it possible to approximate trends in vaccine impact over time.     

Seroprevalence of SARS-CoV-2 IgG Antibodies and Factors Associated with SARS-CoV-2 IgG Neutralizing Activity among Primary Health Care Workers 6 Months after Vaccination Rollout in France

We aimed to investigate the immunoglobulin G response and neutralizing activity against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) among primary health care workers (PHCW) in France and assess the association between the neutralizing activity and several factors, including the coronavirus disease 2019 (COVID-19) vaccination scheme. A cross-sectional survey was conducted between 10 May 2021 and 31 August 2021. Participants underwent capillary blood sampling and completed a questionnaire. Sera were tested for the presence of antibodies against the nucleocapsid (N) protein and the S-1 portion of the spike (S) protein and neutralizing antibodies. In total, 1612 PHCW were included. The overall seroprevalences were: 23.6% (95% confidence interval (CI) 21.6–25.7%) for antibodies against the N protein, 94.7% (93.6–95.7%) for antibodies against the S protein, and 81.3% (79.4–83.2%) for neutralizing antibodies. Multivariate regression analyses showed that detection of neutralizing antibodies was significantly more likely in PHCW with previous SARS-CoV-2 infection than in those with no such history among the unvaccinated (odds ratio (OR) 16.57, 95% CI 5.96–59.36) and those vaccinated with one vaccine dose (OR 41.66, 95% CI 16.05–120.78). Among PHCW vaccinated with two vaccine doses, the detection of neutralizing antibodies was not significantly associated with previous SARS-CoV-2 infection (OR 1.31, 95% CI 0.86–2.07), but was more likely in those that received their second vaccine dose within the three months before study entry than in those vaccinated more than three months earlier (OR 5.28, 95% CI 3.51–8.23). This study highlights that previous SARS-CoV-2 infection and the time since vaccination should be considered when planning booster doses and the design of COVID-19 vaccine strategies.     

Enhanced national surveillance of severe acute respiratory infections (SARI) within COVID-19 surveillance,Slovenia, weeks 13 to 37 2021

We monitored trends of severe COVID-19 morbidity in Slovenia during weeks 13 to 37 2021. National weekly rates of severe acute respiratory infections (SARI) cases testing positive for SARS-CoV-2 at admission in all hospitals varied between 0.2 and 16.3 cases per 100,000 population. Of those without previous COVID-19 diagnosis, SARI COVID-19 admission rates ranged between 0.3 and 17.5 per 100,000 unvaccinated, and 0.0 and 7.3 per 100,000 fully vaccinated individuals. National SARI COVID-19 surveillance is essential in informing COVID-19 response.     

Multisystem Inflammatory Syndrome in Children: The impact of vaccination status on importation of COVID-19 among international travellers

Governments worldwide are looking for ways to safely enable international travel while mitigating the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the associated coronavirus disease 2019 (COVID-19). However, few data describe the impact of vaccination on importation of COVID-19. We took advantage of the sequential introduction of two government policies in Canada to evaluate the real-world evidence of vaccine effectiveness among 30,361 international travellers arriving by air in Alberta, Canada. The proportion of COVID-19-positive results for travellers who were either fully vaccinated or partially vaccinated was 0.02% (95% CI: 0.00–0.10) (i.e. one positive case among 5,817 travellers). In contrast, 1.42% (95% CI: 1.27–1.58) of unvaccinated travellers tested positive for SARS-CoV-2 (341 cases among 24,034 travellers). These findings suggest that COVID-19 vaccinations approved in Canada, substantially reduced the risk of travel-related importation of COVID-19 when combined with other public health measures. The low absolute rate of infection among fully vaccinated or partially vaccinated international travellers may inform quarantine requirements in this population.     

Association of Reduced Hospitalizations and Mortality Rates Among COVID-19-Vaccinated Patients With Heart Failure

BackgroundPatients with heart failure (HF) are at high risk for adverse outcomes when they have COVID-19. Reports of COVID-19 vaccine-related cardiac complications may contribute to vaccine hesitancy in patients with HF.MethodsTo analyze the impact of COVID-19 vaccine status on clinical outcomes in patients with HF, we conducted a retrospective cohort study of the association of COVID-19 vaccination status with hospitalizations, intensive care unit admission and mortality after adjustment for covariates. Inverse probability treatment-weighted models were used to adjust for potential confounding.ResultsOf 7094 patients with HF, 645 (9.1%) were partially vaccinated, 2200 (31.0%) were fully vaccinated, 1053 were vaccine-boosted (14.8%), and 3196 remained unvaccinated (45.1%) by January 2022. The mean age was 73.3 ± 14.5 years, and 48% were female. Lower mortality rates were observed in patients who were vaccine-boosted, followed by those who were fully vaccinated; they experienced lower mortality rates (HR 0.33; CI 0.23, 0.48) and 0.36 (CI 0.30, 0.43), respectively, compared to unvaccinated individuals (P< 0.001) over the mean follow-up time of 276.5 ± 104.9 days, whereas no difference was observed between those who were unvaccinated or only partially vaccinated.ConclusionCOVID-19 vaccination was associated with significant reduction in all-cause hospitalization rates and mortality rates, lending further evidence to support the importance of vaccination implementation in the high-risk population of patients living with HF.     

SARS-CoV-2 primary and breakthrough infections in patients with cancer: Implications for patient care

Initial reports of SARS-CoV-2 caused COVID-19 suggested that patients with malignant diseases were at increased risk for infection and its severe consequences. In order to provide early United States population-based assessments of SARS-CoV-2 primary infections in unvaccinated patients with hematologic malignancies or cancer, and SARS-CoV-2 breakthrough infections in vaccinated patients with hematologic malignancies or cancer, we conducted retrospective studies using two, unique nationwide electronic health records (EHR) databases. Using these massive databases to provide highly statistically significant data, our studies demonstrated that, compared to patients without malignancies, risk for COVID-19 was increased in patients with all cancers and with all hematologic malignancies. Risks varied with specific types of malignancy. Patients with hematologic malignancies or cancer were at greatest risk for COVID-19 during the first year after diagnosis. Risk for infection was increased for patients 65 years and older, compared to younger patients and among Black patients compared to white patients.When patients with hematologic malignancies or cancer were vaccinated against SARS-CoV-2, their risk for breakthrough infections was decreased relative to primary infections but remained elevated relative to vaccinated patients without malignancies. Compared to vaccinated patients without malignancies, vaccinated patients with hematologic malignancy or cancer showed increased risk for infection at earlier post vaccination time points. As with primary infections, risk for breakthrough infections was greatest in patients during their first year of hematologic malignancy or cancer. There were no signs of racial disparities among vaccinated patients with hematologic malignancies or cancer. These results provide the population basis to understand the significance of subsequent immunologic studies showing relative defective and delayed immunoresponsiveness to SARS-CoV-2 vaccines among patients with hematologic malignancies and cancers. These studies further provide the basis for recommendations regarding COVID-19 vaccination, vigilance and maintaining mitigation strategies in patients with hematologic malignancies and cancers.     

Early and Longitudinal Humoral Response to the SARS-CoV-2 mRNA BNT162b2 Vaccine in Healthcare Workers: Significance of BMI,Adipose Tissue and Muscle Mass on Long-Lasting Post-Vaccinal Immunity

Background: This study aimed to investigate the early and longitudinal humoral response in Healthcare Workers (HCWs) after two doses of the BNT162b2 vaccine and to assess the association between metabolic and anthropometric parameters and the humoral response after vaccination. Methods: The study included 243 fully vaccinated HCWs: 25.50% previously infected with SARS-CoV-2 (with prior history of COVID-19—PH) and 74.40%—uninfected, seronegative before the first vaccination (with no prior history of COVID-19—NPH). IgG antibodies were measured, and sera were collected: prior to the vaccination, 21 days after the first dose, and 14 days and 8 months after the second dose. Results: 21 days after the first dose, 90.95% of individuals were seropositive; 14 days after the second dose, persistent immunity was observed in 99.18% HCWs, 8 months after complete vaccination—in 61.73%. Statistical analysis revealed that HCWs with PH had a greater chance of maintaining a humoral response beyond eight months after vaccination. Increased muscle mass, decreased fat mass, and younger age may positively affect long-term immunity. Smokers have a reduced chance of developing immunity compared to non-smokers. Conclusions: Fully vaccinated HCWs with PH are more likely to be seropositive than fully inoculated volunteers with NPH.     

The Association of Social Factors and Health Insurance Coverage with COVID-19 Vaccinations and Hesitancy,July 2021

BackgroundThere are racial differences in COVID-19 vaccination rates, but social factors, such as lack of health insurance or food insecurity, may explain some of the racial disparities.ObjectiveTo assess social factors, including insurance coverage, that may affect COVID-19 vaccination as of June–July 2021 and vaccine hesitancy among those not yet vaccinated, and how these may affect racial equity in vaccinations.DesignCross-sectional analysis of nationally representative survey data.ParticipantsAdults 18 to 64 participating in the Census Bureau’s Household Pulse Survey for June 23 to July 5, 2021.Main MeasuresVaccination: receipt of at least one dose of a COVID-19 vaccine. Vaccine hesitancy: among those not yet vaccinated, intent to definitely or probably not get vaccinated.Key ResultsIn unadjusted analyses, black adults were less likely to be vaccinated than other respondents, but, after social factors were included, including health insurance status, food sufficiency, income and education, and state-level political preferences, differences between black and white adults were no longer significant and Hispanics were more likely to be vaccinated (OR = 1.87, p < .001). Among those not yet vaccinated, black and Hispanic adults were vaccine hesitant than white adults (ORs = .37 and .45, respectively, both p < .001) and insurance status and food insufficiency were not significantly associated with vaccine hesitancy. The percent of state voters for former President Trump in 2020 was significantly associated with lower vaccination rates and with increased vaccine hesitancy.DiscussionThe results indicate that much of the gap in COVID vaccination rates for minority adults are due to social barriers, rather than differences in racial attitudes. Unvaccinated minority adults expressed less vaccine hesitancy than white adults. Social barriers like food insecurity and insurance coverage could have deterred prompt COVID-19 vaccinations. Reducing these problems might help increase vaccination rates.     

Covid-19 vaccine acceptance,hesitancy, and refusal among Canadian healthcare workers: A multicenter survey

BackgroundDeterminants of COVID-19 vaccine acceptance among healthcare workers (HCW) remains poorly understood. We assessed HCWs’ willingness to be vaccinated and reasons underlying hesitancy.MethodsCross-sectional survey across 17 healthcare institutions. HCWs eligible for vaccination (Pfizer-BioNTech mRNA) in December 2020 were invited to receive immunization. Multivariate logistic regression was performed to identify predictors of acceptance. Reasons for refusal among those who never intended to be vaccinated (ie, firm refusers) and those who preferred delaying vaccination (ie, vaccine hesitants) were assessed.ResultsAmong 2,761 respondents (72% female, average age, 44), 2,233 (80.9%) accepted the vaccine. Physicians, environmental services workers and healthcare managers were more likely to accept vaccination compared to nurses. Male sex, age over 50, rehabilitation center workers, and occupational COVID-19 exposure were independently associated with vaccine acceptance by multivariate analysis. Factors for refusal included vaccine novelty, wanting others to receive it first, and insufficient time for decision-making. Among those who declined, 74% reported they may accept future vaccination. Vaccine firm refusers were more likely than vaccine hesitants to distrust pharmaceutical companies and to prefer developing a natural immunity by getting COVID-19.ConclusionsVaccine hesitancy exists among HCWs. Our findings provide useful information to plan future interventions and improve acceptance.     

Prevalence of Anti-SARS-CoV-2 Specific Antibodies in Health-Care Workers Compared to General Population during an Early Phase of the Pandemic,Tehran-Iran

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly transmits in general population, mainly between health-care workers (HCWs) who are in close contact with patients. Objective: To study the seropositivity of HCWs as a high-risk group compared to general population. Methods: 72 samples were obtained from HCWs working in Masih Daneshvari hospital as one of the main COVID-19 admission centers in Tehran, during April 4 to 6, 2020. Also we collected 2021 blood samples from general population. The SARS-CoV-2 specific IgM, and IgG antibodies in the collected serum specimens were measured by commercial ELISA kits. Results: Based on the clinical manifestations, 25.0%, 47.2%, and 27.8% of HCWs were categorized as symptomatic with typical symptoms, symptomatic with atypical symptoms, and asymptomatic, respectively. Symptomatic individuals with typical and atypical symptoms were 63.2% and 36.8% positive in RT-PCR test, respectively. Anti-SARS-CoV-2 IgM and IgG antibodies were detected in 15.3% and 27.8% of HCWs samples, respectively. Antibody testing in the general population indicated that SARS-CoV-2 specific IgM and IgG were found in (162/2021) 8%, and (290/2021) 14.4%, respectively. The frequency of positive cases of IgM and IgG were significantly increased in HCWs compared to general population (p= 0.028 for IgM and p= 0.002 for IgG). Conclusion: The frequency of SARS-CoV-2 specific antibodies in HCWs was higher than general population indicating a higher viral transmission via close exposure with COVID-19 patients.     

Vaccine effectiveness against SARS-CoV-2 transmission and infections among household and other close contacts of confirmed cases,the Netherlands,February to May 2021

Several studies report high effectiveness of COVID-19 vaccines against SARS-CoV-2 infection and severe disease, however an important knowledge gap is the vaccine effectiveness against transmission (VET). We present estimates of the VET to household and other close contacts in the Netherlands, from February to May 2021, using contact monitoring data. The secondary attack rate among household contacts was lower for fully vaccinated than unvaccinated index cases (11% vs 31%), with an adjusted VET of 71% (95% confidence interval: 63–77).     

Effectiveness and safety of pandemic influenza A (H1N1) 2009 vaccine in healthcare workers at a university hospital in Japan

Pandemic influenza A (H1N1) virus (AH1pdm) emerged in April 2009. An inactivated, split-virus, unadjuvanted AH1pdm vaccine was manufactured in Japan, and vaccination was initiated with top priority for healthcare workers (HCWs) on October 19, 2009. A retrospective cohort study was conducted to evaluate the effectiveness of a single-dose vaccine for HCWs in a hospital in Japan. A total of 1,567 (84.5%) of 1,854 HCWs were vaccinated. Thirty-seven were infected with AH1pdm before the vaccine became available, and were excluded. The other 250 were not vaccinated for personal reasons. We analyzed the influenza infection rate with or without vaccination and related adverse events. Among the 1,817 HCWs without previous infection, 37 were infected with AH1pdm; 13 (5.2%) of 250 unvaccinated HCWs became infected, which was a significantly higher rate than the 24 (1.5%) of 1,567 vaccinated HCWs (P=0.001). Multivariate analysis revealed that age of 20-29 years was a risk factor for infection (adjusted odds ratio [aOR], 3.7; P<0.001), and that vaccination was a preventive factor (aOR, 0.20; P<0.001). Adverse events occurred in 549 of 1,060 HCWs, but most were mild. Although vaccination was carried out during AH1pdm epidemic expansion, the single-dose AH1pdm vaccine proved effective in HCWs, and severe adverse events were rare.     

High SARS-CoV-2 Prevalence among Healthcare Workers in Cochabamba,Bolivia

Healthcare workers (HCWs) are at increased risk of SARS-CoV-2 infection. The aim of the study was to estimate the SARS-CoV-2 seroprevalence among HCWs in Cochabamba, Bolivia and to determine the potential risk factors. In January 2021, a cross-sectional SARS-CoV-2 seroprevalence study was conducted in 783 volunteer clinical and non-clinical HCWs in tertiary care facilities. It was based on IgG detection using ELISA, chemiluminiscence, and seroneutralisation tests from dried blood spots. Analysis revealed a high seroprevalence (43.4%) of SARS-CoV-2 IgG antibodies. The combination of anosmia and ageusia (OR: 68.11; 95%-CI 24.83–186.80) was predictive of seropositivity. Belonging to the cleaning staff (OR: 1.94; 95%-CI 1.09–3.45), having more than two children in the same house (OR: 1.74; 95%-CI 1.12–2.71), and having been in contact with a close relative with COVID-19 (OR: 3.53; 95%-CI 2.24–5.58) were identified as risk factors for seropositivity in a multivariate analysis. A total of 47.5% of participants had received medication for COVID-19 treatment or prevention, and only ~50% of symptomatic subjects accessed PCR or antigenic testing. This study confirms a massive SARS-CoV-2 attack rate among HCWs in Cochabamba by the end of January 2021. The main risk factors identified are having a low-skilled job, living with children, and having been in contact with an infected relative in the household.     

Evolution of seroprevalence to SARS-CoV-2 in blood donors in Sarajevo Canton,Federation of Bosnia and Herzegovina: Cross-sectional and longitudinal studies

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

One thousand fifteen 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 re-infected 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.     

High SARS-CoV-2 Seroprevalence among Healthcare Workers in Bamako,Mali

In Mali, a country in West Africa, cumulative confirmed COVID-19 cases and deaths among healthcare workers (HCWs) remain enigmatically low, despite a series of waves, circulation of SARS-CoV-2 variants, the country’s weak healthcare system, and a general lack of adherence to public health mitigation measures. The goal of the study was to determine whether exposure is important by assessing the seroprevalence of anti-SARS-CoV-2 IgG antibodies in HCWs. The study was conducted between November 2020 and June 2021. HCWs in the major hospitals where COVID-19 cases were being cared for in the capital city, Bamako, Mali, were recruited. During the study period, vaccinations were not yet available. The ELISA of the IgG against the spike protein was optimized and quantitatively measured. A total of 240 HCWs were enrolled in the study, of which seropositivity was observed in 147 cases (61.8%). A continuous increase in the seropositivity was observed, over time, during the study period, from 50% at the beginning to 70% at the end of the study. HCWs who provided direct care to COVID-19 patients and were potentially highly exposed did not have the highest seropositivity rate. Vulnerable HCWs with comorbidities such as obesity, diabetes, and asthma had even higher seropositivity rates at 77.8%, 75.0%, and 66.7%, respectively. Overall, HCWs had high SARS-CoV-2 seroprevalence, likely reflecting a “herd” immunity level, which could be protective at some degrees. These data suggest that the low number of cases and deaths among HCWs in Mali is not due to a lack of occupational exposure to the virus but rather related to other factors that need to be investigated.     

Seroprevalence,Waning and Correlates of Anti-SARS-CoV-2 IgG Antibodies in Tyrol,Austria: Large-Scale Study of 35,193 Blood Donors Conducted between June 2020 and September 2021

There is uncertainty about the seroprevalence of anti-SARS-CoV-2 antibodies in the general population of Austria and about the waning of antibodies over time. We conducted a seroepidemiological study between June 2020 and September 2021, enrolling blood donors aged 18–70 years across Tyrol, Austria (participation rate: 84.0%). We analyzed serum samples for antibodies against the spike or the nucleocapsid proteins of SARS-CoV-2. We performed a total of 47,363 samples taken from 35,193 individuals (median age, 43.1 years (IQR: 29.3–53.7); 45.3% women; 10.0% with prior SARS-CoV-2 infection). Seroprevalence increased from 3.4% (95% CI: 2.8–4.2%) in June 2020 to 82.7% (95% CI: 81.4–83.8%) in September 2021, largely due to vaccination. Anti-spike IgG seroprevalence was 99.6% (95% CI: 99.4–99.7%) among fully vaccinated individuals, 90.4% (95% CI: 88.8–91.7%) among unvaccinated individuals with prior infection and 11.5% (95% CI: 10.8–12.3%) among unvaccinated individuals without known prior infection. Anti-spike IgG levels were reduced by 44.0% (95% CI: 34.9–51.7%) at 5–6 months compared with 0–3 months after infection. In fully vaccinated individuals, they decreased by 31.7% (95% CI: 29.4–33.9%) per month. In conclusion, seroprevalence in Tyrol increased to 82.7% in September 2021, with the bulk of seropositivity stemming from vaccination. Antibody levels substantially and gradually declined after vaccination or infection.