To accurately interpret COVID-19 seroprevalence surveys, knowledge of serum-IgG responses to SARS-CoV-2 with a better understanding of patients who do not seroconvert, is imperative. This study aimed to describe serum-IgG responses to SARS-CoV-2 in a cohort of patients with both severe and mild COVID-19, including extended studies of patients who remained seronegative more than 90 days post symptom onset. SARS-CoV-2-specific IgG antibody levels were quantified using two clinically validated and widely used commercial serological assays (Architect, Abbott Laboratories and iFlash 1800, YHLO), detecting antibodies against the spike and nucleocapsid proteins. Forty-seven patients (mean age 49 years, 38% female) were included. All (15/15) patients with severe symptoms and 29/32 (90.6%) patients with mild symptoms of COVID-19 developed SARS-CoV-2-specific IgG antibodies in serum. Time to seroconversion was significantly shorter (median 11 vs. 22 days, P = 0.04) in patients with severe compared to mild symptoms. Of the three patients without detectable IgG-responses after >90 days, all had detectable virus-neutralizing antibodies and in two, spike-protein receptor binding domain-specific IgG was detected with an in-house assay. Antibody titers were preserved during follow-up and all patients who seroconverted, irrespective of the severity of symptoms, still had detectable IgG levels >75 days post symptom onset. Patients with severe COVID-19 both seroconvert earlier and develop higher concentrations of SARS-CoV-2-specific IgG than patients with mild symptoms. Of those patients who not develop detectable IgG antibodies, all have detectable virus-neutralizing antibodies, suggesting immunity. Our results showing that not all COVID-19 patients develop detectable IgG using two validated commercial clinical methods, even over time, are vital for the interpretation of COVID-19 seroprevalence surveys.

Studies on sociodemographic disparities in Covid-19 vaccination uptake in the general population are still limited and mostly focused on older adults. This study examined sociodemographic differences in Covid-19 vaccination uptake in the total Swedish population aged 18–64 years. National Swedish register data within the SCIFI-PEARL project were used to cross-sectionally investigate sociodemographic differences in Covid-19 vaccination among Swedish adults aged 18–64 years (n = 5,987,189) by 12 October 2021. Using logistic regression models, analyses were adjusted for sociodemographic factors, region of residence, history of Covid-19, and comorbidities. An intersectional analysis approach including several cross-classified subgroups was used to further address the complexity of sociodemographic disparities in vaccination uptake. By 12 October 2021, 76·0% of the Swedish population 18–64 years old had received at least two doses of Covid-19 vaccine, an additional 5·5% had received only one dose, and 18·5% were non-vaccinated. Non-vaccinated individuals were, compared to vaccinated, more often younger, male, had a lower income, were not gainfully employed, and/or were born outside Sweden. The social patterning for vaccine dose two was similar, but weaker, than for dose one. After multivariable adjustments, findings remained but were attenuated indicating the need to consider different sociodemographic factors simultaneously. The intersectional analysis showed a large variation in vaccine uptake ranging from 32% to 96% in cross-classified subgroups, reflecting considerable sociodemographic heterogeneity in vaccination coverage. Our study, addressing the entire Swedish population aged 18–64 years, showed broad sociodemographic disparities in Covid-19 vaccine uptake but also wide heterogeneities in coverage. The intersectional analysis approach indicates that focusing on specific sociodemographic factors in isolation and group average risks without considering the heterogeneity within such groups will risk missing the full variability of vaccine coverage. SciLifeLab / Knut & Alice Wallenberg Foundation, Swedish Research Council, Swedish government ALF agreement, FORMAS.

It has been hypothesised that the measles-mumps-rubella (MMR) vaccine may afford cross-protection against SARS-CoV-2 which may contribute to the wide variability in disease severity of Covid-19. We employed a test negative case-control study, utilising a recent measles outbreak during which many healthcare workers received the MMR vaccine, to investigate the potential protective effect of MMR against SARS-CoV-2 in 5905 subjects (n = 805 males, n = 5100 females). The odds ratio for testing positive for SARS-CoV-2, in recently MMR-vaccinated compared to not recently MMR-vaccinated individuals was 0.91 (95% CI 0.76, 1.09). An interaction analysis showed a significant interaction for sex. After sex-stratification, the odds ratio for testing positive for males was 0.43 (95% CI 0.24, 0.79, P = 0.006), and 1.01 (95% CI 0.83, 1.22, P = 0.92) for females. Our results indicate that there may be a protective effect of the MMR vaccine against SARS-CoV-2 in males but not females.

The objective of this study was to provide a comprehensive characterization of patients diagnosed with post-COVID-19 condition (PCC) during the first 16 months of use of the International Classification of Diseases revision 10 (ICD-10) diagnosis code U09.9 in Sweden. We used data from national registers and primary health care databases for all adult inhabitants of the two largest regions in Sweden, comprising 4.1 million inhabitants (approximately 40% of the Swedish population). We present the cumulative incidence and incidence rate of PCC overall and among subgroups and describe patients with COVID-19 with or without PCC regarding sociodemographic characteristics, comorbidities, subsequent diseases, COVID-19 severity, and virus variants. Of all registered COVID-19 cases available for PCC diagnosis (n = 506,107), 2.0% (n = 10,196) had been diagnosed with PCC using ICD-10 code U09.9 as of February 15, 2022 in the two largest regions in Sweden. The cumulative incidence was higher among women than men (2.3% vs 1.6%, P <0.001). The majority of PCC cases (n = 7162, 70.2%) had not been hospitalized for COVID-19. This group was more commonly female (69.9% vs 52.9%, P <0.001), had a tertiary education (51.0% vs 44.1%, P <0.001), and was older (median age difference 5.7 years, P <0.001) than non-hospitalized patients with COVID-19 without PCC. This characterization furthers the understanding of patients diagnosed with PCC and could support policy makers with appropriate societal and health care resource allocation.