SARS-CoV-2 antibody levels and long COVID occurrence in blood donors.

BACKGROUND: Long COVID is a common condition lacking consensus definition; determinants remain incompletely understood. Characterizing immune profiles associated with long COVID could support the development of preventive and therapeutic strategies. METHODS: We used a survey to investigate blood donors' infection/vaccination history and acute/persistent symptoms following COVID-19. The prevalence of long COVID was evaluated using self-report and an adapted definition from the RECOVER study. We evaluated factors associated with long COVID, focusing on anti-spike and anti-nucleocapsid SARS-CoV-2 antibodies. Lastly, we investigated long COVID clinical subphenotypes using hierarchical clustering. RESULTS: Of 33,610 participants, 16,003 (48%) reported having had COVID-19; 1853 (12%) had self-reported long COVID, 685 (4%) met an adapted RECOVER definition, and 2050 (13%) met at least one definition. Higher anti-nucleocapsid levels measured 12-24 weeks post-infection were associated with higher risk of self-reported and RECOVER long COVID. Higher anti-spike IgG levels measured 12-24 weeks post-infection were associated with lower risk of self-reported long COVID. Higher total anti-spike measured 24-48 weeks post-infection was associated with lower risk of RECOVER long COVID. Cluster analysis identified four clinical subphenotypes; patterns included neurological and psychiatric for cluster 1; neurological and respiratory for cluster 2; multi-systemic for cluster 3; and neurological for cluster 4. DISCUSSION: Long COVID prevalence in blood donors varies depending on the adopted definition. Anti-SARS-CoV-2 antibodies were time-dependently associated with long COVID; higher anti-nucleocapsid levels were associated with higher risk; and higher anti-spike levels were associated with lower risk of long COVID. Different underlying pathophysiologic mechanisms may be associated with distinct clinical subphenotypes.

Differences in SARS-CoV-2 antibodies depending on age, blood group, and sex in a Swedish blood donor cohort.

This study aimed to describe differences in prevalence and the long-term presence of nucleocapsid antibodies (N-antibodies) elicited by SARS-CoV-2 infection in a Swedish blood donor population not subjected to lockdown. We tested 20,651 blood donor samples for nucleocapsid antibodies from the beginning of March 2020 and 27 months onwards using the Roche Elecsys Anti-SARS-CoV-2 assay. The proportion of positive SARS-CoV-2 antibody samples was determined each week. After the exclusions of one-time donors and subjects with incomplete data, 19,726 samples from 4003 donors remained. Differences in antibody prevalences stratified for age, sex, and blood groups (ABO and RhD) were determined, as well as antibody loss and recovery. Lower antibody prevalence was seen for older donors, blood group AB, and RhD-negative subjects. A significant decrease in antibody titer between the first and the second antibody-positive donation was seen for the whole study group, females, older subjects, blood group O, AB, and RhD-positive subjects. The titer waned below the detection limit in 60 (3.0%) of 1983 N-antibody-positive donors, and for 18 of these donors, a second episode with antibodies was detected. We showed that N-antibodies persist for months or years and that surprisingly few antibody-positive donors lost their antibodies. We also conclude that antibody prevalence in a Swedish population never subject to lockdown did not apparently differ from populations that were subject to stricter regulations.

Acceptability of self-administered antigen test for COVID-19 in the Philippines.

OBJECTIVES: In response to the Omicron surge in early 2022, the HTA Philippines evaluated the acceptability of Filipinos in using self-administered antigen tests (SAAgTs) as part of COVID-19 HTAs in the Philippines. METHODS: Scoping review from literature databases was initially conducted to identify preset codes in the use of SAAgT. Preset codes were used to establish the questions for focus group discussions (FGDs). Semi-structured questionnaires were created through Delphi technique. FGDs with four stakeholder groups (i.e., nine healthcare workers [HCWs], seven representatives of at-risk groups, six economic frontliners, and seven representatives of micro-small-medium-sized enterprises) were conducted. RESULTS: Discomfort in being a target of stigma and being prescribed an "illness identity" when suspected or confirmed COVID-19-positive, along with lack of confidence to perform self-test, caused hesitancy in self-testing among participants. The need for subsidies for test kits from the government or employers was emphasized to increase its accessibility. Having a designated access point and reporting system for SAAgT was highlighted to avoid nepotism (padrino system attributed to debt of gratitude), inequitable distribution, and lapses in reporting. A participatory approach to education was perceived as crucial to reduce any misconceptions associated with the use of SAAgT. CONCLUSIONS: All FGD groups expressed favorable reviews on the implementation of SAAgT because it can potentially reduce the burden of health facility-administered tests. These findings were considered by the HTA Council in the recommendation of SAAgT as part of the overarching national strategies for the diagnosis and screening of COVID-19.

Longitudinal study comparing IgG antibodies induced by heterologous prime-boost COVID-19 vaccine.

Vaccines are critical cost-effective tools to control the COVID-19 pandemic. The heterologous prime-boost vaccination has been used by many countries to overcome supply issues, so the effectiveness and safety of this strategy need to be better clarified. This study aims to verify the effect of heterologous prime-boost COVID-19 vaccination on healthcare professionals from Dante Pazzanese Hospital in Brazil. It was performed serological assays of vaccinated individuals after 2-dose of CoronaVac (Sinovac; n = 89) or ChAdOx1 nCoV-19 (Oxford-AstraZeneca; n = 166) followed by a BNT162b2 booster (Pfizer-BioNTech; n = 255). The serum antibodies anti-S (spike), anti-N (nucleocapsid), and anti-RBD (receptor binding domain) were assessed by enzyme-linked immunosorbent assay. The heterologous booster dose induced a 10-fold higher anti-Spike antibody regardless of the 2-dose of a prime vaccine. It was strikingly observed that BNT162b2 enhanced levels of anti-spike antibodies, even in those individuals who did not previously respond to the 2-dose of CoronaVac. In conclusion, the heterologous scheme of vaccination using mRNA as a booster vaccine efficiently enhanced the antibody response against SARS-CoV-2, especially benefiting those elderly who were seronegative with a virus-inactivated vaccine.

Two-phase Bayesian latent class analysis to assess diagnostic test performance in the absence of a gold standard: COVID-19 serological assays as a proof of concept.

BACKGROUND AND OBJECTIVES: In this proof-of-concept study, which included blood donor samples, we aimed to demonstrate how Bayesian latent class models (BLCMs) could be used to estimate SARS-CoV-2 seroprevalence in the absence of a gold standard assay under a two-phase sampling design. MATERIALS AND METHODS: To this end, 6810 plasma samples from blood donors who resided in Québec (Canada) were collected from May to July 2020 and tested for anti-SARS-CoV-2 antibodies using seven serological assays (five commercial and two non-commercial). RESULTS: SARS-CoV-2 seroprevalence was estimated at 0.71% (95% credible interval [CrI] = 0.53%-0.92%). The cPass assay had the lowest sensitivity estimate (88.7%; 95% CrI = 80.6%-94.7%), while the Héma-Québec assay had the highest (98.7%; 95% CrI = 97.0%-99.6%). CONCLUSION: The estimated low seroprevalence (which indicates a relatively limited spread of SARS-CoV-2 in Quebec) might change rapidly-and this tool, developed using blood donors, could enable a rapid update of the prevalence estimate in the absence of a gold standard. Further, the present analysis illustrates how a two-stage BLCM sampling design, along with blood donor samples, can be used to estimate the performance of new diagnostic tests and inform public health decisions regarding a new or emerging disease for which a perfect reference standard does not exist.

Antibody response, associated symptoms and profile of patients presumably infected by SARS-CoV-2 with taste or smell disorders in the SAPRIS multicohort study.

BACKGROUND: Taste or smell disorders have been reported as strongly associated with COVID-19 diagnosis. We aimed to identify subject characteristics, symptom associations, and antibody response intensity associated with taste or smell disorders. METHODS: We used data from SAPRIS, a study based on a consortium of five prospective cohorts gathering 279,478 participants in the French general population. In the analysis, we selected participants who were presumably infected by SARS-CoV-2 during the first epidemic wave. RESULTS: The analysis included 3,439 patients with a positive ELISA-Spike. Sex (OR = 1.28 [95% CI 1.05-1.58] for women), smoking (OR = 1.54 [95% CI 1.13-2.07]), consumption of more than 2 drinks of alcohol a day (OR = 1.37 [95% CI 1.06-1.76]) were associated with a higher probability of taste or smell disorders. The relationship between age and taste or smell disorders was non-linear. Serological titers were associated with taste or smell disorders: OR = 1.31 [95% CI 1.26-1.36], OR = 1.37 [95% CI 1.33-1.42] and OR = 1.34 [95% CI 1.29-1.39] for ELISA-Spike, ELISA-Nucleocapsid and seroneutralization, respectively. Among participants with taste or smell disorders, 90% reported a wide variety of other symptoms whereas 10% reported no other symptom or only rhinorrhea. CONCLUSIONS: Among patients with a positive ELISA-Spike test, women, smokers and people drinking more than 2 drinks a day were more likely to develop taste or smell disorders. This symptom was strongly associated with an antibody response. The overwhelming majority of patients with taste or smell disorders experienced a wide variety of symptoms.

Sequential IgG antibody monitoring for virus-inactivated and adenovirus-vectored COVID-19 vaccine in Brazilian healthcare workers.

Vaccination certainly is the best way to fight against the COVID-19 pandemic. In this study, the seroconversion effectiveness of two vaccines against severe acute respiratory syndrome coronavirus 2 was assessed in healthcare workers: virus-inactivated CoronaVac (CV, n = 303), and adenovirus-vectored Oxford-AstraZeneca (AZ, n = 447). The immunoglobulin G (IgG) antibodies anti-spike glycoprotein and anti-nucleocapsid protein were assessed by enzyme-linked immunosorbent assay at the time before vaccination (T1), before the second dose (T2), and 30 days after the second dose (T3). Of all individuals vaccinated with AZ, 100% (n = 447) exhibited seroconversion, compared to 91% (n = 276) that were given CV vaccine. Among individuals who did not respond to the CV, only three individuals showed a significant increase in the antibody level 4 months later the booster dose. A lower seroconversion rate was observed in elders immunized with the CV vaccine probably due to the natural immune senescence, or peculiarity of this vaccine. The AZ vaccine induced a higher humoral response; however, more common side effects were also observed. Nonvaccinated convalescent individuals revealed a similar rate of anti-spike IgG to individuals that were given two doses of CV vaccine, which suggests that only a one-shot COVID-19 vaccine could produce an effective immune response in convalescents.

Saliva as a diagnostic specimen for SARS-CoV-2 detection: A scoping review.

OBJECTIVES: This scoping review aims to summarize the diagnostic value of saliva assessed from current studies that (1) compare its performance in reverse transcriptase-polymerase chain reaction testing to nasopharyngeal swabs, (2) evaluate its performance in rapid and point-of-care COVID-19 diagnostic tests, and (3) explore its use as a specimen for detecting anti-SARS-CoV-2 antibodies. MATERIALS AND METHODS: A systematic search was performed on the following databases: Medline and Embase (Ovid), World Health Organization, Centers for Disease Control and Prevention, and Global Health (Ovid) from January 2019 to September 2021. Of the 657 publications identified from the searches, n = 146 articles were included in the final scoping review. RESULTS: Our findings showcase that salivary samples exceed nasopharyngeal swabs in detecting SARS-CoV-2 using reverse transcriptase-polymerase chain reaction testing in several studies. A select number of rapid antigen and point-of-care tests from the literature were also identified capable of high detection rates using saliva. Moreover, anti-SARS-CoV-2 antibodies have been shown to be detectable in saliva through biochemical assays. CONCLUSION: We highlight the potential of saliva as an all-rounded specimen in detecting SARS-CoV-2. However, future large-scale clinical studies will be needed to support its widespread use as a non-invasive clinical specimen for COVID-19 testing.

Indicators of recent COVID-19 infection status: findings from a large occupational cohort of staff and postgraduate research students from a UK university.

BACKGROUND: Researchers conducting cohort studies may wish to investigate the effect of episodes of COVID-19 illness on participants. A definitive diagnosis of COVID-19 is not always available, so studies have to rely on proxy indicators. This paper seeks to contribute evidence that may assist the use and interpretation of these COVID-indicators. METHODS: We described five potential COVID-indicators: self-reported core symptoms, a symptom algorithm; self-reported suspicion of COVID-19; self-reported external results; and home antibody testing based on a 'lateral flow' antibody (IgG/IgM) test cassette. Included were staff and postgraduate research students at a large London university who volunteered for the study and were living in the UK in June 2020. Excluded were those who did not return a valid antibody test result. We provide descriptive statistics of prevalence and overlap of the five indicators. RESULTS: Core symptoms were the most common COVID-indicator (770/1882 participants positive, 41%), followed by suspicion of COVID-19 (n = 509/1882, 27%), a positive symptom algorithm (n = 298/1882, 16%), study antibody lateral flow positive (n = 124/1882, 7%) and a positive external test result (n = 39/1882, 2%), thus a 20-fold difference between least and most common. Meeting any one indicator increased the likelihood of all others, with concordance between 65 and 94%. Report of a low suspicion of having had COVID-19 predicted a negative antibody test in 98%, but positive suspicion predicted a positive antibody test in only 20%. Those who reported previous external antibody tests were more likely to have received a positive result from the external test (24%) than the study test (15%). CONCLUSIONS: Our results support the use of proxy indicators of past COVID-19, with the caveat that none is perfect. Differences from previous antibody studies, most significantly in lower proportions of participants positive for antibodies, may be partly due to a decline in antibody detection over time. Subsequent to our study, vaccination may have further complicated the interpretation of COVID-indicators, only strengthening the need to critically evaluate what criteria should be used to define COVID-19 cases when designing studies and interpreting study results.

Prevalence of SARS-CoV-2 antibodies in Denmark: nationwide, population-based seroepidemiological study.

Seroprevalence studies have proven an important tool to monitor the progression of the coronavirus disease 2019 (COVID-19) pandemic. We present results of consecutive population-based seroprevalence surveys performed in Denmark in 2020. In spring, late summer and autumn/winter of 2020, invitation letters including a questionnaire covering symptoms were sent to representative samples of the population above 12 years and to parents of children below 18 years in the sample. Blood samples were analysed for total Ig and seroprevalence estimates per population segment were calculated and compared to other surveillance parameters. Based on 34 081 participants (participation rate 33%), seroprevalence estimates increased from 1.2% (95%CI: 0.3-1.9%) in May to 4.1% (95%CI: 3.1-4.9%) in December 2020. Seroprevalence estimates were roughly three times higher in those aged 12-29 years compared to 65 + and higher in metropolitan municipalities. By December 2020, 1.5% of the population had tested positive by RT-PCR. Infected individuals in older age groups were hospitalised several fold more often than in younger. Amongst seropositives, loss of taste/smell were the more specific symptoms, 32-56% did not report any symptoms. In more than half of seroconverted families, we did not see evidence of transmission between generations. Seroprevalence increased during 2020; adolescents were primarily infected in the autumn/winter. Denmark has a high per capita test rate; roughly one undiagnosed infection of SARS-CoV-2 were estimated to occur for each diagnosed case. Approximately half were asymptomatically infected. The epidemic appears to have progressed relatively modestly during 2020 in Denmark.

Kinetics of Anti-SARS-CoV-2 IgG among healthcare workers in a General Hospital.

SARS-CoV-2 is a newly-discovered positive-sense RNA virus, the cause of coronavirus disease 2019 (COVID-19) currently spreading worldwide. The SARS-CoV-2 S glycoprotein is considered a main target for neutralizing antibodies. In order to better understand the kinetics of the antibody response, we evaluated the relation between two consecutive antibody titers determined over an average period of four months. A total of 628 subjects were included in the study. A significant reduction of the antibody titers over time was found: Ab Titer 1: 8.1 Arbitrary Units (AU)/mL (IQR: 4.8-29.3); Ab Titer 2: 6.2 AU/mL (IQR: 0-28.5); p<0.0001. A Receiver Operator Characteristic curve analysis showed an Area Under the Curve (AUC) of 0.973 (95% CI: 0.962-0.984; p<0.0001) with an Ab titer 1 threshold of 110 AU/mL to predict an Ab Titer 2 ≥50 AU/mL with 100% specificity. Likewise, an AUC of 0.952 (95% CI: 0.930-0.974; p<0.0001) with an Ab titer 1 threshold of 185 AU/mL was found to predict an Ab Titer 2 ≥100 AU/mL. This study showed that the SARS-CoV-2 S1/S2 IgG median titer declined over an average period of four months and that the first IgG determination thresholds found can help predict IgG values after the same interval.

[Effectiveness and safety of COVID-19 vaccines in healthcare workers in Buenos Aires City, Argentina.] / Efectividad y seguridad de las vacunas contra la Covid-19 en trabajadores de la salud en la Ciudad de Buenos Aires, Argentina.

Introduction: COVID-19 vaccination aids pandemic limitation. In Argentina, three vaccines are approved, and healthcare workers are priorized (HCWs). The aim was to determine the effectiveness of COVID-19 vaccines, analyzing change in Immunoglobulin G levels and the incidence of new COVID-19 cases up to 12 months after the second dose. Methods: Prospective cohort of HCWs between March 2021- 2022. COVIDAR IgG test was used to measure antibodies. A mixed-effects model was employed to compare the levels of immunoglobulin G at different time points, Kaplan Meier was used to estimate incident COVID-19 cases. Results: 82 participants were included Adverse events were frequent but mild. All participant showed positive antibody at 12 months. Antibodies levels showed an increase one year after 2nd dose. Sinopharm took a long time to yield positive results. More than half of the people had mild COVID-19 disease. Conclusion: COVID-19 vaccines are safe and effective.

Introducción: La vacunación COVID-19 ayuda a limitar la pandemia. En Argentina, se aprobaron tres vacunas y se priorizó a los trabajadores de la salud (TDS). El objetivo fue determinar la efectividad de las vacunas COVID-19, analizando el cambio en los niveles de Inmunoglobulina G y la incidencia de nuevos casos de COVID-19 hasta 12 meses después de la segunda dosis. Métodos: Cohorte prospectiva de TDS entre marzo de 2021 y 2022. Se utilizó la prueba COVIDAR IgG para medir los anticuerpos. Se empleó un modelo de efectos mixtos para comparar los niveles de inmunoglobulina G en diferentes puntos temporales, se utilizó Kaplan Meier para estimar los casos de COVID-19 incidentes. Resultados: se incluyeron 82 participantes. Los eventos adversos fueron frecuentes pero leves. Todos los participantes mostraron anticuerpos positivos a los 12 meses. Los niveles de anticuerpos mostraron un aumento un año después de la segunda dosis. Sinopharm tardó mucho tiempo en arrojar resultados positivos. Más de la mitad de las personas tuvieron una enfermedad leve de COVID-19. Conclusión: Las vacunas COVID-19 son seguras y efectivas.

Nine-Month Trend of IgG Antibody Persistence and Associated Symptoms Post-SARS-CoV-2 Infection.

Between 2 and 8.5% of patients who recover from COVID-19 do not develop antibodies, and the durability of IgG antibodies is under scrutiny. Therefore, the presence and persistence of IgM and IgG antibodies were evaluated in a group of patients diagnosed with SARS-CoV-2 from May to August 2020. Out of 2199 suspected COVID-19 cases, 1264 were confirmed for SARS-CoV-2 by rRT-PCR; 328 consented to participate in the study, with 220 participants followed for 9 months, including 124 men (56%) and 96 women (44%). The primary symptoms were headache, dry cough, and fever. IgG antibodies developed in 95% of patients within 4 weeks post-diagnosis, and a second evaluation at 9 months showed that 72.7% still had detectable IgG antibodies. The presence of IgM in one individual (0.45%) suggested the possibility of reinfection.

Association between severe acute respiratory syndrome coronavirus 2 antibody status and reinfection: A case-control study nested in a Colorado-based prospective cohort study.

The association between the presence of detectable antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and SARS-CoV-2 reinfection is not well established. The objective of this study was to determine the association between antibody seronegativity and reinfection. METHODS: Participants in Colorado, USA, were recruited between June 15, 2020, and March 28, 2021, and encouraged to complete SARS-CoV-2 molecular ribonucleic acid (RNA) and serology testing for antibodies every 28 days for 10 months. Participants with reinfections (positive SARS-CoV-2 RNA test ≥ 90 days after the first positive RNA test) were matched to controls without reinfections by age, sex, date of the first positive RNA test, date of the last serology test, and serology test type. Using conditional logistic regression, case patients were compared to control patients on the last serologic test result, with adjustment for demographic and clinical confounders. RESULTS: The cohort (n = 4,235) included 2,033 participants with ≥ 1 positive RNA test, of whom 120 had reinfection. Among the 80 case patients who could be matched, the last serologic test was negative in 12 of the cases (15.0 %) whereas the last serologic test was negative in 77 of 1,034 (7.5 %) controls. Seronegativity (adjusted OR [aOR] 2.24; 95 % CI 1.07, 4.68), Hispanic ethnicity (aOR 1.87; 95 % 1.10, 3.18), and larger household size (aOR 1.15; 95 % 1.01, 1.30 for each additional household member) were associated with reinfection. CONCLUSIONS: Seronegative status, Hispanic ethnicity, and increasing household size were associated with reinfection. Serologic testing could be considered to reduce vaccine hesitancy in higher risk populations.

SARS CoV-2 seroprevalence and diagnostic accuracy during a COVID-19 outbreak in a major penitentiary complex in Brazil, June to July 2020.

PURPOSE: This study aims to estimate the overall SARS-CoV-2 seroprevalence and evaluate the accuracy of an antibody rapid test compared to a reference serological assay during a COVID-19 outbreak in a prison complex housing over 13,000 prisoners in Brasília. DESIGN/METHODOLOGY/APPROACH: The authors obtained a randomized, stratified representative sample of each prison unit and conducted a repeated serosurvey among prisoners between June and July 2020, using a lateral-flow immunochromatographic assay (LFIA). Samples were also retested using a chemiluminescence enzyme immunoassay (CLIA) to compare SARS-CoV-2 seroprevalence and 21-days incidence, as well as to estimate the overall infection fatality rate (IFR) and determine the diagnostic accuracy of the LFIA test. FINDINGS: This study identified 485 eligible individuals and enrolled 460 participants. Baseline and 21-days follow-up seroprevalence were estimated at 52.0% (95% CI 44.9-59.0) and 56.7% (95% CI 48.2-65.3) with LFIA; and 80.7% (95% CI 74.1-87.3) and 81.1% (95% CI 74.4-87.8) with CLIA, with an overall IFR of 0.02%. There were 78.2% (95% CI 66.7-89.7) symptomatic individuals among the positive cases. Sensitivity and specificity of LFIA were estimated at 43.4% and 83.3% for IgM; 46.5% and 91.5% for IgG; and 59.1% and 77.3% for combined tests. ORIGINALITY/VALUE: The authors found high seroprevalence of anti-SARS-CoV-2 antibodies within the prison complex. The occurrence of asymptomatic infection highlights the importance of periodic mass testing in addition to case-finding of symptomatic individuals; however, the field performance of LFIA tests should be validated. This study recommends that vaccination strategies consider the inclusion of prisoners and prison staff in priority groups.

Characteristics of COVID-19 vaccinated and unvaccinated patients admitted to Careggi University Hospital, Florence, Italy.

More than 11.5 billion COVID-19 vaccine doses have been administered around the world. Although vaccine effectiveness for severe infections is reported to be 89.0%, breakthrough infections are common and may lead to severe outcome in fragile population. We conducted a real-world observational study on 420 COVID-19 admitted patients from July 2021 to January 2022 in a tertiary level Italian hospital. We collected patient's vaccination and SARS-CoV-2 serological status, SARS-CoV-2 treatments, oxygen supports, intensive (ICU) and subintensive (sub-ICU) care unit admissions, length of staying (LoS) and in-hospital mortality. One-hundred-seventy-two vaccinated and 248 unvaccinated patients were admitted during the study period. Vaccinated group (Vg) had a significantly more elevated Charlson Comorbidity Index than Unvaccinated group (UVg), and no statistical differences were found in terms of in-hospital mortality, LoS or ICU and sub-ICU admissions. Among Vg, anti-S antibodies were detected in 86.18% of patients (seropositives). Vaccinated seronegative patients' in-hospital mortality was significantly higher than vaccinated seropositive patients (33.33% vs 10.69%, p = 0.0055): in particular, mortality rate in 45-69 years old population was higher in vaccinated seronegative group, and comparable in patients ≥ 70 years old. No differences in terms of outcome were registered between Vg and UVg, taking into account that Vg was considerably older and with more comorbidities. In line with other recent observations, higher mortality rate was evidenced for seronegative vaccinated patients. Primary prophylaxis and early treatments result to be necessary, especially for older and immunosuppressed populations.

Seroprevalence of SARS-CoV-2 Antibodies in Denmark: Results of Two Nationwide Population-Based Surveys, February and May 2021.

Background: Seroprevalence studies can be used to measure the progression of national COVID-19 epidemics. The Danish National Seroprevalence Survey of SARS-CoV-2 infections (DSS) was conducted as five separate surveys between May 2020 and May 2021. Here, we present results from the two last surveys conducted in February and May 2021. Methods: Persons aged 12 or older were randomly selected from the Danish Population Register and those having received COVID-19 vaccination subsequently excluded. Invitations to have blood drawn in local test centers were sent by mail. Samples were analyzed for whole Immunoglobulin by ELISA. Seroprevalence was estimated by sex, age and geography. Comparisons to vaccination uptake and RT-PCR test results were made. Results: In February 2021, we found detectable antibodies in 7.2% (95% CI: 6.3-7.9%) of the invited participants (participation rate 25%) and in May 2021 in 8.6% (95% CI: 7.6-9.5%) of the invited (participation rate: 14%). Seroprevalence did not differ by sex, but by age group, generally being higher among the <50 than 50+ year-olds. In May 2021, levels of seroprevalence varied from an estimated 13% (95% CI: 12-15%) in the capital to 5.2% (95% CI: 3.4-7.4%) in rural areas. Combining seroprevalence results with vaccine coverage, estimates of protection against infection in May 2021 varied from 95% among 65+ year-olds down to 10-20% among 12-40 year-olds. In March-May 2021, an estimated 80% of all community SARS-CoV-2 infections were diagnosed by RT-PCR and captured by surveillance. Conclusion: Seroprevalence estimates doubled during the 2020-21 winter wave of SARS-CoV-2 infections and then stabilized as vaccinations were rolled out. The epidemic affected large cities and younger people the most. Denmark saw comparatively low infections rates, but high test coverage; an estimated four out of five infections were detected by RT-PCR in March-May 2021.

Correction to "Performance of a serological IgM and IgG qualitative test for COVID-19 diagnosis: An experimental study in Brazil".

[This corrects the article on p. 100 in vol. 12, PMID: 36196438.].

Analysis of COVID-19 Incidence and Protective Potential of Persisting IgG Class Antibodies against SARS-CoV-2 Infection in Hospital Staff in Poland.

The immune responses to both SARS-CoV-2 infection and vaccines are of key importance in prevention efforts. In April and May 2020, 703 study participants tested for COVID-19 by PCR tests were registered. In June and July 2020, they were examined for the presence of SARS-CoV-2 S1/S2 IgG. From October 2020 to January 2021, those among the study population with COVID-19 confirmed by PCR tests were registered, and the same group of participants was invited to be examined again for the presence of SARS-CoV-2 antibodies. In June 2020, antibodies were detected in only 88% of those who had PCR-confirmed COVID-19 in April-May 2020, which suggests that a significant proportion of persons in the Polish population do not produce antibodies after contact with SARS-CoV-2 antigens or rapidly lose them and reach levels below the lab detection limit. The levels of IgG class anti-SARS-CoV-2 antibodies were significantly lower among people who previously had COVID-19 than for those who had received COVID-19 vaccination, which confirms the high immunogenicity of the vaccines against COVID-19 in the Polish population. The study confirms that a detectable level of IgG class anti-SARS-CoV-2 antibodies cannot be considered a reliable marker of the presence and strength of COVID-19 immunity preventing individuals from acquiring SARS-CoV-2 infection.

SARS-CoV-2 antibodies persist up to 12 months after natural infection in healthy employees working in non-medical contact-intensive professions.

OBJECTIVES: This study aimed to evaluate dynamics of antibody levels after exposure to SARS-CoV-2 for 12 months in Dutch non-vaccinated hairdressers and hospitality staff. METHODS: In this prospective cohort study, blood samples were collected every 3 months for 1 year and analyzed using a qualitative total antibody enzyme-linked immunosorbent assay (ELISA) and a quantitative immunoglobulin (Ig)G antibody ELISA. Participants completed questionnaires, providing information on demographics, health, and work. Differences in antibody levels were evaluated using Mann-Whitney U and Wilcoxon signed-rank tests. Beta coefficients (ß) and 95% confidence intervals (CIs) were calculated using linear regression. RESULTS: Ninety-five of 497 participants (19.1%) had ≥1 seropositive measurement before their last visit using the qualitative ELISA. Only 2.1% (2/95) seroreverted during follow-up. Of 95 participants, 82 (86.3%) tested IgG seropositive in the quantitative ELISA too. IgG antibody levels significantly decreased in the first months (P <0.01) but remained detectable for up to 12 months in all participants. Older age (ß, 10-years increment: 24.6, 95% CI: 5.7-43.5) and higher body mass index (ß, 5kg/m² increment: 40.0, 95% CI: 2.9-77.2) were significantly associated with a higher peak of antibody levels. CONCLUSION: In this cohort, SARS-CoV-2 antibodies persisted for up to 1 year after initial seropositivity, suggesting long-term natural immunity.