Background, establishment and initial experiences of the Danish cardiovascular homograft biobank.

Odense University Hospital is a major tertiary vascular hospital in Scandinavia, performing approx. 200 aortic repairs annually. This article presents the rationale behind this endeavor and the early outcomes of the initial implantation of locally processed homografts. All patients receiving a homograft were identified from the established homograft biobank database and their medical records were reviewed after obtaining consent. All surgeons in charge of homograft implantations were semi structured interviewed regarding the harvesting procedure, the tools for detecting available homografts, their quality and delivery. The National board of Health approved the biobank fulling the EU Directive of Tissues and Cells after 18 months of preparation. From May 6, 2021, to March 1, 2023, 26 patients had a homograft implantation, with 7 for mycotic aneurysms, 10 for aorto-iliac graft infection, 6 for infra-inguinal graft infection, and 3 for graft infection in thoracic aorta. Six (23%) were emergently performed. Two (7.7%) died within 30 days postoperatively, both following in situ replacement of an infected aortoiliac graft, corresponding to a 20% mortality in this subgroup. The incidence of reinfections was 19.2%; one each in the mycotic aneurysm group, the aortoiliac graft infection group, and the thoracic graft infection group. After 90 days, two patients were diagnosed with aorto-enteric fistula. All involved surgeons could easily identify available suitable homografts, and within 2 h have homografts of acceptable quality and requested dimensions. The establishment of the Danish Cardiovascular Homograft Biobank was straightforward and effectively serves cardiovascular procedures performed 24/7. Additionally, the initial experiences seem comparable to others experiences.

Transplantation of cryopreserved cardiovascular homografts.

Due to degeneration, homografts were since the 1950s only used strictly for replacement of complex arterial segments and lesions incl. the aortic valve, replacement of infected arterial prostheses, and vascular access for patients on haemodialysis. During the 1990s, rate-differentiated freezing methods and anti-crystallization agents proved to prevent crystallisation, and more widespread use with expanded indications incl. coronary and lower limb bypasses began justified by promising midterm results. In 2021, the first Scandinavian homograft biobank was founded in Odense in Denmark. This review summarises the history and the experiences from this biobank.

Hepatitis C screening and linkage to care with a mobile clinic in Southern Denmark.

BACKGROUND: Knowing the prevalence of hepatitis C (HCV) in risk groups is essential for elimination. The aim of the study was to assess HCV prevalence among people with different risk profiles and the feasibility of linking people with HCV to care. METHODS: In Southern Denmark we tested people who were using shelters, cafés, and facilities for marginalized populations and the general population. We established a mobile clinic for HCV testing offering point-of-care HCV-antibody (HCV-Ab), point-of-care HCV RNA testing, and dried blood spot (DBS) testing. People with HCV infection were linked to care. RESULTS: Among 802 tested persons, we found an HCV-Ab /HCV RNA prevalence of 13% (n = 101) /3% (n = 24). We found a prevalence of 20% (n = 97)/5% (n = 24) among 475 persons tested at locations attended by people who inject drugs but 0%/0% when testing the general population. Of 24 people who were HCV RNA positive, 83% (n = 20) initiated treatment, 13% (n = 3) spontaneously cleared their infection, and one was lost to follow-up. CONCLUSION: General population testing has limited utility while focus on settings attended by people with increased HCV risk is more feasible. Linkage of people with a current HCV infection to care is feasible.

Low protection from breakthrough SARS-CoV-2 infection and mild disease course in ocrelizumab-treated patients with multiple sclerosis after three mRNA vaccine doses.

BACKGROUND: Our study investigated the rate of breakthrough SARS-CoV-2 infection and clinical outcomes in a cohort of multiple sclerosis (MS) patients who were treated with the anti-CD20 monoclonal antibody (Ab), ocrelizumab, before first, second and third BNT162b2 mRNA vaccinations. To correlate clinical outcomes with the humoral and cellular response. METHODS: The study was a prospective non-randomised controlled multicentre trial observational study. Participants with a diagnosis of MS who were treated for at least 12 months with ocrelizumab prior to the first BNT162b2 mRNA vaccination were prospectively followed up from January 2021 to June 2022. RESULTS: Out of 54 participants, 32 (59.3%) developed a positive SARS-CoV-2 PCR test in the study period. Mild infection was observed in all infected participants. After the third vaccination, the non-infected participants had higher mean Ab levels compared to the infected participants (54.3 binding antibody unit (BAU)/mL vs 26.5 BAU/mL, p=0.030). The difference in reactivity between spike-specific CD4+ and CD8+ T lymphocytes in the two groups was not significant. CONCLUSION AND RELEVANCE: The study results demonstrate rates of 59% in breakthrough infections after the third SARS-CoV-2 mRNA vaccination in ocrelizumab-treated patients with MS, without resulting in critical disease courses. These findings suggest the need for continuous development of prophylactic treatments when proved important in the protection of severe breakthrough infection.

BQ.1.1, XBB.1, and XBB.1.5 neutralization after bivalent mRNA COVID-19 booster in patients with cancer.

Ehmsen et al. evaluate the neutralizing capacity to current SARS-CoV-2 variants in patients with cancer before and after receiving the BNT162b2 bivalent mRNA vaccine booster. Bivalent vaccine provides some protection against BQ.1.1 but fails to protect against XBB.1 and XBB.1.5 in patients with cancer.

A Cross-Sectional Study of SARS-CoV-2 Antibodies and Risk Factors for Seropositivity in Staff in Day Care Facilities and Preschools in Denmark.

The aim of this study was to provide information about immunity against COVID-19 along with risk factors and behavior among employees in day care facilities and preschools (DCS) in Denmark. In collaboration with the Danish Union of Pedagogues, during February and March 2021, 47,810 members were offered a point-of-care rapid SARS-CoV-2 antibody test (POCT) at work and were invited to fill in an electronic questionnaire covering COVID-19 exposure. Seroprevalence data from Danish blood donors (total Ig enzyme-linked immunosorbent assay [ELISA]) were used as a proxy for the Danish population. A total of 21,018 (45%) DCS employees completed the questionnaire and reported their POCT result {median age, 44.3 years (interquartile range [IQR], [32.7 to 53.6]); females, 84.1%}, of which 20,267 (96.4%) were unvaccinated and included in analysis. A total of 1,857 (9.2%) participants tested seropositive, significantly higher than a seroprevalence at 7.6% (risk ratio [RR], 1.2; 95% confidence interval [CI], 1.14 to 1.27) among 40,541 healthy blood donors (median age, 42 years [IQR, 28 to 53]; males, 51.3%). Exposure at work (RR, 2.9; 95% CI, 2.3 to 3.6) was less of a risk factor than exposure within the household (RR, 12.7; 95% CI, 10.2 to 15.8). Less than 25% of participants reported wearing face protection at work. Most of the participants expressed some degree of fear of contracting COVID-19 both at work and outside work. SARS-CoV-2 seroprevalence was slightly higher in DCS staff than in blood donors, but possible exposure at home was associated with a higher risk than at work. DCS staff expressed fear of contracting COVID-19, though there was limited use of face protection at work. IMPORTANCE Identifying at-risk groups and evaluating preventive interventions in at-risk groups is imperative for the ongoing pandemic as well as for the control of future epidemics. Although DCS staff have a much higher risk of being infected within their own household than at their workplace, most are fearful of being infected with COVID-19 or bringing COVID-19 to work. This represents an interesting dilemma and an important issue which should be addressed by public health authorities for risk communication and pandemic planning. This study design can be used in a strategy for ongoing surveillance of COVID-19 immunity or other infections in the population. The findings of this study can be used to assess the need for future preventive interventions in DCS, such as the use of personal protective equipment.

Omicron BA.5 Neutralization among Vaccine-Boosted Persons with Prior Omicron BA.1/BA.2 Infections.

Worldwide, millions of persons have received multiple COVID-19 vaccinations and subsequently recovered from SARS-CoV-2 Omicron breakthrough infections. In 2 small, matched cohorts (n = 12, n = 24) in Denmark, we found Omicron BA.1/BA.2 breakthrough infection after 3-dose BNT162b2 vaccination provided improved Omicron BA.5 neutralization over 3-dose vaccination alone.

Seroprevalence and infection fatality rate of the SARS-CoV-2 Omicron variant in Denmark: A nationwide serosurveillance study.

Background: Introduction of the Omicron variant caused a steep rise in SARS-CoV-2 infections despite high vaccination coverage in the Danish population. We used blood donor serosurveillance to estimate the percentage of recently infected residents in the similarly aged background population with no known comorbidity. Methods: To detect SARS-CoV-2 antibodies induced due to recent infection, and not vaccination, we assessed anti-nucleocapsid (anti-N) immunoglobulin G (IgG) in blood donor samples. Individual level data on SARS-CoV-2 RT-PCR results and vaccination status were available. Anti-N IgG was measured fortnightly from January 18 to April 3, 2022. Samples from November 2021 were analysed to assess seroprevalence before introduction of the Omicron variant in Denmark. Findings: A total of 43 088 donations from 35 309 Danish blood donors aged 17-72 years were screened. In November 2021, 1·2% (103/8 701) of donors had detectable anti-N IgG antibodies. Adjusting for test sensitivity (estimates ranging from 74%-81%) and November seroprevalence, we estimate that 66% (95% confidence intervals (CI): 63%-70%) of the healthy, similarly aged Danish population had been infected between November 1, 2021, and March 15, 2022. One third of infections were not captured by SARS-CoV-2 RT-PCR testing. The infection fatality rate (IFR) was 6·2 (CI: 5·1-7·5) per 100 000 infections. Interpretation: Screening for anti-N IgG and linkage to national registers allowed us to detect recent infections and accurately assess assay sensitivity in vaccinated or previously infected individuals during the Omicron outbreak. The IFR was lower than during previous waves. Funding: The Danish Ministry of Health.

Immunological Characteristics of Patients Receiving Ultra-Short Treatment for Chronic Hepatitis C.

Reducing the treatment duration for chronic hepatitis C could be an important tool in the effort to reach the elimination goals set by the World Health Organization. The current challenge is to predict the target group who will achieve sustained virological response at week 12 (SVR12) with shorter treatment duration. The aim of this exploratory study was to characterize immune subsets with focus on inhibitory receptors in patients who experienced SVR12 or virological relapse following four weeks treatment with glecaprevir/pibrentasvir with or without ribavirin. A total of 32 patients were included in this study of whom 21 achieved SVR12 and 11 had virological relapse. All available samples at baseline (n = 31) and end of treatment (EOT) (n = 30) were processed for flow cytometric analysis in order to measure the expression of PD-1, 2B4, BY55, CTLA-4, TIM-3 and LAG-3 on 12 distinct T cell subsets. At baseline, patients with SVR12 (n=21) had numerically lower frequencies of inhibitory receptors for 83% (60/72) of the investigated T-cell subtypes. The most significant difference observed between the two groups was a lower frequency of stem cell-like memory T-cells CD4+PD1+ in the SVR group (p = 0.007). Furthermore, we observed a significant positive correlation between baseline viral load and the expression of PD-1 on the total CD8+ T-cells and effector memory T-cells CD4+ and CD8+ for patients with virological relapse. This study suggests a measurable immunologic phenotype at baseline of patients achieving SVR12 after short treatment compared to patients with virological relapse.

SARS-CoV-2 antibody prevalence among homeless people and shelter workers in Denmark: a nationwide cross-sectional study.

BACKGROUND: People experiencing homelessness (PEH) and associated shelter workers may be at higher risk of infection with "Severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2). The aim of this study was to determine the prevalence of SARS-CoV-2 among PEH and shelter workers in Denmark. DESIGN AND METHODS: In November 2020, we conducted a nationwide cross-sectional seroprevalence study among PEH and shelter workers at 21 recruitment sites in Denmark. The assessment included a point-of-care test for antibodies against SARS-CoV-2, followed by a questionnaire. The seroprevalence was compared to that of geographically matched blood donors considered as a proxy for the background population, tested using a total Ig ELISA assay. RESULTS: We included 827 participants in the study, of whom 819 provided their SARS-CoV-2 antibody results. Of those, 628 were PEH (median age 50.8 (IQR 40.9-59.1) years, 35.5% female) and 191 were shelter workers (median age 46.6 (IQR 36.1-55.0) years and 74.5% female). The overall seroprevalence was 6.7% and was similar among PEH and shelter workers (6.8% vs 6.3%, p = 0.87); and 12.2% among all participants who engaged in sex work. The overall participant seroprevalence was significantly higher than that of the background population (2.9%, p < 0.001). When combining all participants who reported sex work or were recruited at designated safe havens, we found a significantly increased risk of seropositivity compared to other participants (OR 2.23, 95%CI 1.06-4.43, p = 0.02). Seropositive and seronegative participants reported a similar presence of at least one SARS-CoV-2 associated symptom (49% and 54%, respectively). INTERPRETATIONS: The prevalence of SARS-CoV-2 antibodies was more than twice as high among PEH and associated shelter workers, compared to the background population. These results could be taken into consideration when deciding in which phase PEH are eligible for a vaccine, as part of the Danish national SARS-CoV-2 vaccination program rollout. FUNDING: TrygFonden and HelseFonden.

Persistently reduced humoral and sustained cellular immune response from first to third SARS-CoV-2 mRNA vaccination in anti-CD20-treated multiple sclerosis patients.

OBJECTIVE: To examine humoral and cellular response in multiple sclerosis patients on anti-CD20 therapy after third BNT162b2 mRNA SARS-CoV-2 vaccination. METHODS: A prospective longitudinal study design from first throughout third vaccination in Danish and American MS centers. All participants were treated with ocrelizumab. Antibody (Ab) levels were assessed before and after third vaccination using SARS-CoV-2 IgG II Quant assay (Abbott Laboratories). B- and T-lymphocytes enumeration was done with BD Multitest™6-color TBNK reagent. Spike-specific T-cell responses were measured through PBMC stimulation with spike peptide pools (JPT Peptide Technologies). RESULTS: We found that 14.0%, 37.7%, and 33.3% were seropositive after first, second and third vaccination. The median Ab-levels were 74.2 BAU/mL (range: 8.5-2427) after second vaccination, as well as 43.7 BAU/ml (range: 7.8-366.1) and 31.3 BAU/mL (range: 7.9-507.0) before and after third vaccination, respectively. No difference was found in levels after second and third vaccination (p = 0.1475). Seropositivity dropped to 25.0% of participants before the third vaccination, a relative reduction of 33.3% (p = 0.0020). No difference was found between frequencies of spike reactive CD4+and CD8+ T-cells after second (0.65 ± 0.08% and 0.95 ± 0.20%, respectively) and third vaccination (0.99 ± 0.22% and 1.3 ± 0.34%, respectively). CONCLUSION: In this longitudinal cohort we found no significant increased humoral or cellular response with administration of a third SARS-CoV-2 mRNA vaccination. These findings suggest the need for clinical strategies to include allowance of B cell reconstitution before repeat vaccination and/or provision of pre-exposure prophylactic monoclonal antibodies.

Four Weeks Treatment with Glecaprevir/Pibrentasvir + Ribavirin-A Randomized Controlled Clinical Trial.

Enhancing treatment uptake for hepatitis C to achieve the elimination goals set by the World Health Organization could be achieved by reducing the treatment duration. The aim of this study was to compare the sustained virological response at week 12 (SVR12) after four weeks of glecaprevir/pibrentasvir (GLE/PIB) + ribavirin compared to eight weeks of GLE/PIB and to estimate predictors for SVR12 with four weeks of treatment through a multicenter open label randomized controlled trial. Patients were randomized 2:1 (4 weeks:8 weeks) and stratified by genotype 3 and were treatment naïve of all genotypes and without significant liver fibrosis. A total of 27 patients were analyzed for predictors for SVR12, including 15 from the first pilot phase of the study. In the 'modified intention to treat' group, 100% (7/7) achieved cure after eight weeks and for patients treated for four weeks the SVR12 was 58.3% (7/12). However, patients with a baseline viral load <2 mill IU/mL had 93% SVR12. The study closed prematurely due to the low number of included patients due to the COVID-19 pandemic. Our results suggest that viral load should be taken into account when considering trials of short course treatment.

A multi-level intervention to eliminate hepatitis C from the Region of Southern Denmark: the C-Free-South project.

Denmark has signed the WHO strategy to eliminate hepatitis C virus (HCV). In the absence of a national strategy for elimination, a local action plan was developed in the Region of Southern Denmark (RSD). The aim of the strategy is to diagnose 90% of HCV-infected persons and treat 80% of those diagnosed by 2025. The strategy was developed by reviewing Danish data on HCV epidemiology and drug use to identify key populations for screening, linkage to care, and treatment. Based on available published data from 2016, an estimated 3028 persons in the RSD were HCV-RNA positive (population prevalence 0.21%). Of these, 1002 were attending clinical care, 1299 were diagnosed but not in clinical care, and 727 were undiagnosed. Three different interventions targeting the HCV-infected population and two interventions for HCV surveillance are planned to achieve elimination. The "C-Free-South" strategy aims to eliminate HCV in our region by identifying (90%) and treating (80%) of infected persons by the end of 2025, 5 years earlier than the WHO elimination target date.

Seroprevalence of SARS-CoV-2 antibodies in social housing areas in Denmark.

BACKGROUND: COVID-19 is thought to be more prevalent among ethnic minorities and individuals with low socioeconomic status. We aimed to investigate the prevalence of SARS-CoV-2 antibodies during the COVID-19 pandemic among citizens 15 years or older in Denmark living in social housing (SH) areas. METHODS: We conducted a study between January 8th and January 31st, 2021 with recruitment in 13 selected SH areas. Participants were offered a point-of-care rapid SARS-CoV-2 IgM and IgG antibody test and a questionnaire concerning risk factors associated with COVID-19. As a proxy for the general Danish population we accessed data on seroprevalence from Danish blood donors (total Ig ELISA assay) in same time period. RESULTS: Of the 13,279 included participants, 2296 (17.3%) were seropositive (mean age 46.6 (SD 16.4) years, 54.2% female), which was 3 times higher than in the general Danish population (mean age 41.7 (SD 14.1) years, 48.5% female) in the same period (5.8%, risk ratios (RR) 2.96, 95% CI 2.78-3.16, p > 0.001). Seropositivity was higher among males (RR 1.1, 95% CI 1.05-1.22%, p = 0.001) and increased with age, with an OR seropositivity of 1.03 for each 10-year increase in age (95% CI 1.00-1.06, p = 0.031). Close contact with COVID-19-infected individuals was associated with a higher risk of infection, especially among household members (OR 5.0, 95% CI 4.1-6.2 p < 0,001). Living at least four people in a household significantly increased the OR of seropositivity (OR 1.3, 95% CI 1.0-1.6, p = 0.02) as did living in a multi-generational household (OR 1.3 per generation, 95% CI 1.1-1.6, p = 0.003). Only 1.6% of participants reported not following any of the national COVID-19 recommendations. CONCLUSIONS: Danish citizens living in SH areas of low socioeconomic status had a three times higher SARS-CoV-2 seroprevalence compared to the general Danish population. The seroprevalence was significantly higher in males and increased slightly with age. Living in multiple generations households or in households of more than four persons was a strong risk factor for being seropositive. Results of this study can be used for future consideration of the need for preventive measures in the populations living in SH areas.

Long-term detection of SARS-CoV-2 antibodies after infection and risk of re-infection.

OBJECTIVES: To evaluate long-term sensitivity for detection of total antibodies against SARS-CoV-2 METHODS: From week 41, 2020, through week 26, 2021, all Danish blood donations were tested for SARS-CoV-2 antibodies with the Wantai assay. The results were linked with polymerase chain reaction (PCR) test results from the Danish Microbiological Database (MiBa). RESULTS: During the study period, 105,646 non-vaccinated Danish blood donors were tested for SARS-CoV-2 antibodies, and 3,806 (3.6%) had a positive PCR test before the blood donation. Among the donors with a positive PCR test, 94.2% subsequently also had a positive antibody test. The time between the positive PCR test and the antibody test was up to 15 months and there was no evidence of a decline in proportion with detectable antibodies over time. A negative serological result test was associated with a higher incidence of re-infection (Incidence Rate Ratio = 0.102 (95% confidence interval (CI): 0.039-0.262)). CONCLUSION: Among healthy blood donors, 94.2% developed SARS-CoV-2 antibodies after infection, and a lack of detectable antibodies was associated with re-infection.

SARS-CoV-2 antibody kinetics in blood donors with a previously positive SARS-CoV-2 antibody test within a seroprevalence survey.

The persistence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies is a matter of importance regarding the coronavirus disease 19 (COVID-19) pandemic. To observe antibody dynamics, 105 blood donors, positive for SARS-CoV-2 antibodies by a lateral flow test within a seroprevalence study, were included in this study. Thirty-nine (37%) of 105 the donors were confirmed positive by a total Ig Wantai enzyme-linked immunosorbent assay (ELISA). Three (8%) in this group of 39 reported severe and 26/39 (67%) mild to moderate COVID-19 symptoms. By further ELISA-testing, 33/39 (85%) donors were initially positive for IgG antibodies, 31/39 (79%) for IgA, and 32/39 (82%) for IgM, while 27/39 (69%) were positive for all three isotypes. Persistence of IgG, IgA, and IgM was observed in 73%, 79%, and 32% of donors, respectively, after 6-9 months of observation. For IgM antibodies, the decline in the proportion of positive donors was statistically significant (p = 0.002) during 12 months observation, for IgG only the decline at 3 months was statistically significant (p = 0.042). Four donors exhibited notable increases in antibody levels. In conclusion, persistent SARS-CoV-2 IgA antibodies and IgG antibodies at 6-9 months are present in approximately three of four individuals with previous mild to moderate COVID-19.

Estimation of SARS-CoV-2 Infection Fatality Rate by Age and Comorbidity Status Using Antibody Screening of Blood Donors During the COVID-19 Epidemic in Denmark.

BACKGROUND: Studies presenting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection fatality rate (IFR) for healthy individuals are warranted. We estimate IFR by age and comorbidity status using data from a large serosurvey among Danish blood donors and nationwide data on coronavirus disease 2019 (COVID-19) mortality. METHODS: Danish blood donors aged 17-69 years donating blood October 2020-February 2021 were tested with a commercial SARS-CoV-2 total antibody assay. IFR was estimated for weeks 11 to 42, 2020 and week 43, 2020 to week 6, 2021, representing the first 2 waves of COVID-19 epidemic in Denmark. RESULTS: In total, 84944 blood donors were tested for antibodies. The seroprevalence was 2% in October 2020 and 7% in February 2021. Among 3898039 Danish residents aged 17-69 years, 249 deaths were recorded. The IFR was low for people <51 years without comorbidity during the 2 waves (combined IFR=3.36 per 100000 infections). The IFR was below 3‰ for people aged 61-69 years without comorbidity. IFR increased with age and comorbidity but declined from the first to second wave. CONCLUSIONS: In this nationwide study, the IFR was very low among people <51 years without comorbidity.

Humoral immune response following SARS-CoV-2 mRNA vaccination concomitant to anti-CD20 therapy in multiple sclerosis.

BACKGROUND: The immunogenicity of COVID-19 vaccine among patients receiving anti-CD20 monoclonal antibody (Ab) treatment has not been fully investigated. Detectable levels of SARS-CoV-2 immunoglobulin G (IgG) are believed to have a predictive value for immune protection against COVID-19 and is currently a surrogate indicator for vaccine efficacy. OBJECTIVE: To determine IgG Abs in anti-CD20 treated patients with multiple sclerosis (MS). METHOD: IgG Abs against SARS-CoV-2 spike receptor-binding domain were measured with the SARS-CoV-2 IgG II Quant assay (Abbott Laboratories) before and after vaccination (n = 60). RESULTS: 36.7% of patients mounted a positive SARS-CoV-2 spike Ab response after the second dose of vaccine. Five patients (8.3%) developed Abs >264 BAU/mL, another 12 patients (20%) developed intermediate Abs between 54 BAU/mL and 264 BAU/mL and five patients (8.3%) had low levels <54 BAU/mL. Of all seropositive patients, 63.6% converted from seronegative to seropositive after the 2nd vaccine. CONCLUSION: Our study demonstrates decreased humoral response after BNT162b2 mRNA SARS-CoV-2 vaccine in MS patients receiving B-cell depleting therapy. Clinicians should advise patients treated with anti-CD20 to avoid exposure to SARS-CoV-2. Future studies should investigate the implications of a third booster vaccine in patients with low or absent Abs after vaccination.

Serum vaccine antibody concentrations in adults exposed to per- and polyfluoroalkyl substances: A birth cohort in the Faroe Islands.

Per- and polyfluoroalkyl substances (PFASs) are highly persistent in the environment and may cause depressed immune function. Previous studies have linked PFAS exposure to lower vaccine responses in children, but research in adults is limited. Therefore, the present study evaluated the associations between exposure to PFASs and serum antibody concentrations in adults vaccinated at age 28 years in the Faroe Islands. PFAS concentrations were determined from cord-blood collected at birth and serum samples collected at ages 7, 14, 22, and 28 years. Serum antibody concentrations against hepatitis type A and B, diphtheria, and tetanus were analyzed from blood samples collected about 6 mo after the first vaccine inoculation at age 28 years. Linear regression models were used to estimate changes in antibody concentration for each doubling of PFAS concentration. Potential effect modification by sex was assessed by including an interaction term between PFAS and sex. Although the 95% confidence intervals contain the null value, inverse trends were observed between serum perfluorooctanoate (PFOA) at ages 14 and 28 years and hepatitis type A antibody (anti-HAV) concentrations, as revealed by an estimated decrease of 0.71 (95% CI: -1.52, 0.09) and 0.24 (95% CI: -0.59, 0.10) signal-to-cutoff ratio for each doubling of exposure, respectively. Inverse trends were also observed between serum PFOA at ages 22 and 28 years and hepatitis type B antibody (anti-HBs) concentration, with an estimated decrease of 21% (95% CI: -42.20%, 7.34%) and of 17% (95% CI: -35.47%, 7.35%) in anti-HBs for each doubling of exposure, respectively. Sex-specific associations with anti-HAV were observed for cord-blood PFASs and serum PFAS concentrations at ages 7 and 14 years. No inverse associations of PFAS exposure were found with diphtheria and tetanus antibody concentrations. Future studies are needed to confirm these findings and further investigate the effects of PFASs on adult immune function.