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Post-acute symptoms are not uncommon after SARS-CoV-2 infection with pre-Omicron variants. How Omicron and COVID-19 booster vaccination influence the risk of post-acute symptoms is less clear. We analyzed data from the nationwide Danish questionnaire study EFTER-COVID comprising 44,553 individuals ≥15 years old, tested between July 2021 and January 2022, in order to evaluate the association of the Omicron variant and COVID-19 booster vaccination with post-acute symptoms and new-onset general health problems, four months after infection with SARS-CoV-2. Risk differences (RDs) were estimated by comparing Omicron -cases to controls, Omicron to Delta -cases, and Omicron vaccinated cases with three to -two doses, adjusted for age, sex, BMI, self-reported chronic diseases, Charlson comorbidity index, healthcare occupation, and vaccination status. Four months after testing for SARS-CoV-2 during the Omicron period, cases experienced substantial post-acute symptoms and new-onset health problems compared to controls; the largest RD was observed for memory issues (RD=7.2%, 95%CI: 6.4 to 8.1). However, risks were generally lower than in the Delta period, particularly for dysosmia (RD=-15.0%, 95%CI: -17.0 to -13.2) and dysgeusia (RD=-11.2%, 95%CI: -13.2 to -9.5). Booster vaccination was associated with fewer post-acute symptoms and new-onset health problems, four months after Omicron infection, compared to two COVID-19 vaccine doses., Post-acute symptoms are not uncommon after SARS-CoV-2 infection with pre-Omicron variants. How Omicron and COVID-19 booster vaccination influence the risk of post-acute symptoms is less clear. We analyzed data from the nationwide Danish questionnaire study EFTER-COVID comprising 44,553 individuals ≥15 years old, tested between July 2021 and January 2022, in order to evaluate the association of the Omicron variant and COVID-19 booster vaccination with post-acute symptoms and new-onset general health problems, four months after infection with SARS-CoV-2. Risk differences (RDs) were estimated by comparing Omicron -cases to controls, Omicron to Delta -cases, and Omicron vaccinated cases with three to -two doses, adjusted for age, sex, BMI, self-reported chronic diseases, Charlson comorbidity index, healthcare occupation, and vaccination status. Four months after testing for SARS-CoV-2 during the Omicron period, cases experienced substantial post-acute symptoms and new-onset health problems compared to controls; the largest RD was observed for memory issues (RD=7.2%, 95%CI: 6.4 to 8.1). However, risks were generally lower than in the Delta period, particularly for dysosmia (RD=-15.0%, 95%CI: -17.0 to -13.2) and dysgeusia (RD=-11.2%, 95%CI: -13.2 to -9.5). Booster vaccination was associated with fewer post-acute symptoms and new-onset health problems, four months after Omicron infection, compared to two COVID-19 vaccine doses.

Importance: Fatigue remains one of the most common and debilitating symptoms of post-COVID-19 condition; however, existing studies are limited to select populations and often lack noninfected controls. It also remains unclear to what extent severity of infection and psychiatric conditions, which are often linked to chronic fatigue, modify the risk of post-COVID-19 condition fatigue symptoms. Objective: To evaluate the impact of SARS-CoV-2 infection on self-reported fatigue and postexertional malaise over time and to explore possible risk factors, such as the impact of acute SARS-CoV-2 hospitalization and preexisting psychiatric conditions on postacute fatigue. Design, Setting, and Participants: In this cohort study, Danish residents aged 15 years and older were invited to participate in the EFTER-COVID survey, which used repeated, self-reported online questionnaires that collected information on fatigue (Fatigue Assessment Scale) and postexertional malaise scores (DePaul Symptom Questionnaire) after individuals' index SARS-CoV-2 polymerase chain reaction test. Participants were included if they completed a baseline and at least 1 follow-up questionnaire 2 to 18 months after testing for SARS-CoV-2. Exposure: Testing for SARS-CoV-2 infection. Main Outcomes and Measures: The primary outcomes were fatigue and postexertional malaise 2 to 18 months after testing. Mixed-effects models were used to compare scores between SARS-CoV-2 test-positive and test-negative individuals (testing period April 2021 to February 2023). Results: Of a total of 50 115 participants (median [IQR] age at test date, 57 [46-67] years; 29 774 female [59.4%]), 25 249 were test positive and 24 866 were test negative. Most participants were vaccinated with at least 2 doses (21 164 test-negative participants [85.1%] and 22 120 test-positive participants [87.6%]) before their SARS-CoV-2 index test and fatigue reporting. In the period 2 to 18 months after testing, SARS-CoV-2 infection was associated w

We appreciate the opportunity to respond to the four comments by Porsbjerg et al. regarding our study on long-term effectiveness of pollen allergen immunotherapy (AIT) in stopping intranasal corticosteroid (INCS) use during the pollen season.1 We observed effectiveness was limited to the first five of 18 years studied.

OBJECTIVES: To investigate the associations of physical activity (PA) and sedentary behaviour in early childhood with asthma and reduced lung function in later childhood within a large collaborative study. DESIGN: Pooling of longitudinal data from collaborating birth cohorts using meta-analysis of separate cohort-specific estimates and analysis of individual participant data of all cohorts combined. SETTING: Children aged 0-18 years from 26 European birth cohorts. PARTICIPANTS: 136 071 individual children from 26 cohorts, with information on PA and/or sedentary behaviour in early childhood and asthma assessment in later childhood. MAIN OUTCOME MEASURE: Questionnaire-based current asthma and lung function measured by spirometry (forced expiratory volume in 1 s (FEV1), FEV1/forced vital capacity) at age 6-18 years. RESULTS: Questionnaire-based and accelerometry-based PA and sedentary behaviour at age 3-5 years was not associated with asthma at age 6-18 years (PA in hours/day adjusted OR 1.01, 95% CI 0.98 to 1.04; sedentary behaviour in hours/day adjusted OR 1.03, 95% CI 0.99 to 1.07). PA was not associated with lung function at any age. Analyses of sedentary behaviour and lung function showed inconsistent results. CONCLUSIONS: Reduced PA and increased sedentary behaviour before 6 years of age were not associated with the presence of asthma later in childhood.

Background and Aims To demonstrate that administration of 7500 Trichuris suis ova [TSO] every second week over 24 weeks would reduce the intestinal inflammation in moderate ulcerative colitis. Methods A single-centre, randomised, double-blinded, placebo-controlled, phase 2b clinical trial of 7500 Trichuris suis ova every 2 weeks for 24 weeks compared with placebo in moderate activity of ulcerative colitis [Mayo score 6–10] were performed. Primary outcome: clinical remission; secondary outcomes: clinical response at 24 weeks, complete corticosteroid-free clinical remission, endoscopic remission, symptomatic remission at 12 and 24 weeks, and partial Mayo score over time. Results In all, 119 patients were randomised to Trichuris suis ova [n = 60] or placebo [n = 59]. At Week 24, clinical remission was achieved in 30% of Trichuris suis ova-treated vs 34% of placebo-treated (risk ratio [RR] = 0.89; 95% confidence interval [CI]: 0.52–1.50; p = 0.80, intention to treat). No difference was found in clinical response in any of the clinical response subgroups. However, in patients who did not need treatment with corticosteroids during the trial, a temporary effect of TSO was seen in the analysis of symptomatic remission at Week 12 [p = 0.01] and the partial Mayo score at Week 14 and Week 18 [p < 0.05 and p = 0.02]. Conclusions Compared with placebo, Trichuris suis ova administration was not superior in achieving clinical remission at Week 24 in ulcerative colitis or in achieving clinical Mayo score reduction, complete corticosteroid-free clinical remission, or endoscopic remission. However, Trichuris suis ova treatment induced symptomatic temporary remission at Week 12.

Objectives To investigate the associations of physical activity (PA) and sedentary behaviour in early childhood with asthma and reduced lung function in later childhood within a large collaborative study.Design Pooling of longitudinal data from collaborating birth cohorts using meta-analysis of separate cohort-specific estimates and analysis of individual participant data of all cohorts combined.Setting Children aged 0-18 years from 26 European birth cohorts.Participants 136 071 individual children from 26 cohorts, with information on PA and/or sedentary behaviour in early childhood and asthma assessment in later childhood.Main outcome measure Questionnaire-based current asthma and lung function measured by spirometry (forced expiratory volume in 1 s (FEV1), FEV1/forced vital capacity) at age 6-18 years.Results Questionnaire-based and accelerometry-based PA and sedentary behaviour at age 3-5 years was not associated with asthma at age 6-18 years (PA in hours/day adjusted OR 1.01, 95% CI 0.98 to 1.04; sedentary behaviour in hours/day adjusted OR 1.03, 95% CI 0.99 to 1.07). PA was not associated with lung function at any age. Analyses of sedentary behaviour and lung function showed inconsistent results.Conclusions Reduced PA and increased sedentary behaviour before 6 years of age were not associated with the presence of asthma later in childhood., Funding Agencies|Netherlands Organisation for Health Research and Development (ZonMW); Netherlands Heart Foundation; Swedish Research Council [K2005-72X-11242-11A, K2008-69X-20826-01-4]; Swedish Child Diabetes Foundation (Barndiabetesfonden); JDRF Wallenberg Foundation [K 98-99D-12813-01A]; Medical Research Council of Southeast Sweden (FORSS); Swedish Council for Working Life and Social Research [FAS2004-1775]; Ostgota Brandstodsbolag; Swedish Research Council; Swedish Research Council for Health, Working Life and Welfare, Formas; Swedish Heart-Lung Foundation; Swedish Asthma and Allergy Research Foundation; Region Stockholm (ALF project, and for cohort and database maintenance); European Research Council (TRIBAL) [757919]; Commission of the European Community; European Union; Project EarlyNutrition [289346]; Polish Ministry of Science and Higher Education [2571/7.PR/2012/2]; EU H2020 project PHC-2014-DynaHealth [633595]; European Research Council [322605]; COPSAC; Lundbeck Foundation [R16-A1694]; Ministry of Health [903516]; Danish Council for Strategic Research [0603-00280B]; Capital Region Research Foundation; Danish National Research Foundation; Danish Regional Committees; Pharmacy Foundation; Egmont Foundation; March of Dimes Birth Defects Foundation; Health Foundation; Novo Nordisk Foundation; Lundbeck Foundation; National Institute for Research in Public Health; National Agency for Research (ANR non-thematic programme); French Speaking Association for the Study of Diabetes and Metabolism (Alfediam); Mutuelle Generale de l'Education Nationale; Nestle; French National Institute for Health Education (INPES); Paris-Sud University; French National Istitute for Population Health Surveillance (InVS); French Agency for Environment Security (AFFSET); French Ministry of Health Perinatal Program; Inserm Nutrition Research Program; Institut Federatif de Recherche and Cohort Program; French Ministry of Research; EURIP and FIRE doctoral school-Programme Bettencourt; Fon

Purpose To follow SARS-CoV-2-infected persons up to 18 months after a positive test in order to assess the burden and nature of post acute symptoms and health problems. Participants Persons in Denmark above 15 years of age, who were tested positive for SARS-CoV-2 during 1 September 2020 to 21 February 2023 using a RT-PCR test. As a reference group, three test-negative individuals were selected for every two test-positive individuals by matching on test date. Findings to date In total, 2 427 913 invitations to baseline questionnaires have been sent out and 839 528 baseline questionnaires (34.5%) have been completed. Females, the age group 50–69 years, Danish-born and persons, who had received at least one SARS-CoV-2 vaccination booster dose were more likely to participate. Follow-up questionnaires were sent at 2, 4, 6, 9, 12 and 18 months after the test, with response rates at 42%–54%. Future plans New participants have been recruited on a daily basis from 1 August 2021 to 23 March 2023. Data collection will continue until the last follow-up questionnaires (at 18 months after test) have been distributed in August 2024.

The emergence of bloodstream infections (BSI) caused by vancomycin-resistant Enterococci (VRE) has caused concern.Nonetheless, it remains unclear whether these types are associated with an excess risk of severe outcomes whencompared with infections caused by vancomycin-susceptible Enterococci (VSE). This cohort study includedhospitalized patients in Denmark with Enterococcus faecium-positive blood cultures collected between 2010 and 2019identified in the Danish Microbiology Database. We estimated 30-day hazard ratio (HR) of death or discharge amongVRE compared to VSE patients adjusted for age, sex, and comorbidity. The cohort included 6071 patients withE. faecium BSI (335 VRE, 5736 VSE) among whom VRE increased (2010–13, 2.6%; 2014–16, 6.3%; 2017–19; 9.4%).Mortality (HR 1.08, 95%CI 0.90–1.29; 126 VRE, 37.6%; 2223 VSE, 37.0%) or discharge (HR 0.89, 95%CI 0.75–1.06; 126VRE, 37.6%; 2386 VSE, 41.6%) was not different between VRE and VSE except in 2014 (HR 1.87, 95% CI 1.18–2.96).There was no interaction between time from admission to BSI (1–2, 3–14, and >14 days) and HR of death (P = 0.14) ordischarge (P = 0.45) after VRE compared to VSE, despite longer time for VRE patients (17 vs. 10 days for VSE, P <0.0001). In conclusion, VRE BSI was not associated with excess morbidity and mortality. The excess mortality in 2014only may be attributed to improved diagnostic- and patient-management practices after 2014, reducing time toappropriate antibiotic therapy. The high level of mortality after E. faecium BSI warrants further study., The emergence of bloodstream infections (BSI) caused by vancomycin-resistant Enterococci (VRE) has caused concern. Nonetheless, it remains unclear whether these types are associated with an excess risk of severe outcomes when compared with infections caused by vancomycin-susceptible Enterococci (VSE). This cohort study included hospitalized patients in Denmark with Enterococcus faecium-positive blood cultures collected between 2010 and 2019 identified in the Danish Microbiology Database. We estimated 30-day hazard ratio (HR) of death or discharge among VRE compared to VSE patients adjusted for age, sex, and comorbidity. The cohort included 6071 patients with E. faecium BSI (335 VRE, 5736 VSE) among whom VRE increased (2010–13, 2.6%; 2014–16, 6.3%; 2017–19; 9.4%). Mortality (HR 1.08, 95%CI 0.90–1.29; 126 VRE, 37.6%; 2223 VSE, 37.0%) or discharge (HR 0.89, 95%CI 0.75–1.06; 126 VRE, 37.6%; 2386 VSE, 41.6%) was not different between VRE and VSE except in 2014 (HR 1.87, 95% CI 1.18–2.96). There was no interaction between time from admission to BSI (1–2, 3–14, and >14 days) and HR of death (P = 0.14) or discharge (P = 0.45) after VRE compared to VSE, despite longer time for VRE patients (17 vs. 10 days for VSE, P < 0.0001). In conclusion, VRE BSI was not associated with excess morbidity and mortality. The excess mortality in 2014 only may be attributed to improved diagnostic- and patient-management practices after 2014, reducing time to appropriate antibiotic therapy. The high level of mortality after E. faecium BSI warrants further study.

Background Because long-term effectiveness of pollen allergen immune therapy (AIT) for allergic rhinitis (AR) is not well-described, we studied effectiveness over 18 years in Denmark. Methods A register-based cohort study using data on filled prescriptions, 1995–2016, Denmark. In a cohort of 1.1 million intranasal corticosteroid inhaler users (proxy for AR), we matched users treated with grass, birch or mugwort AIT 1:2 with non-treated users on baseline year and 24 characteristics in the 3 years prior to baseline. The primary outcome was the odds ratio (OR) of using anti-allergic nasal inhaler during the pollen season in the treated versus non-treated group by years since baseline. Results Among 7760 AR patients treated with pollen AIT, the OR of using nasal inhaler 0–5 years after baseline was reduced when compared with 15,520 non-treated AR individuals (0–2 years, OR 0.84 (0.81–0.88); 3–5 years, OR 0.88 (0.84–0.92)), but was close to unity or higher thereafter (6–9 years, OR 1.03 (0.97–1.08); 10–18 years, OR 1.18 (1.11–1.26)). In post hoc analyses, results were more consistent for those who already had 3 of 3 baseline years of use, and in patients using nasal inhaler in the latest pollen season (0–2 years, OR 0.76 (0.72–0.79); 3–5 years OR 0.86 (0.81–0.93); 6–9 years, OR 0.94 (0.87–1.02); 10–18 years, OR 0.94 (0.86–1.04)) as opposed to no such use. Conclusions Patients treated with pollen AIT in routine care to a higher degree stopped using anti-allergic nasal inhaler 0–5 years after starting the standard 3 years of therapy, and not beyond 5 years. Post hoc analyses suggested effectiveness was more consistent among patients with persistent AR., Background: Because long-term effectiveness of pollen allergen immune therapy (AIT) for allergic rhinitis (AR) is not well-described, we studied effectiveness over 18 years in Denmark. Methods: A register-based cohort study using data on filled prescriptions, 1995–2016, Denmark. In a cohort of 1.1 million intranasal corticosteroid inhaler users (proxy for AR), we matched users treated with grass, birch or mugwort AIT 1:2 with non-treated users on baseline year and 24 characteristics in the 3 years prior to baseline. The primary outcome was the odds ratio (OR) of using anti-allergic nasal inhaler during the pollen season in the treated versus non-treated group by years since baseline. Results: Among 7760 AR patients treated with pollen AIT, the OR of using nasal inhaler 0–5 years after baseline was reduced when compared with 15,520 non-treated AR individuals (0–2 years, OR 0.84 (0.81–0.88); 3–5 years, OR 0.88 (0.84–0.92)), but was close to unity or higher thereafter (6–9 years, OR 1.03 (0.97–1.08); 10–18 years, OR 1.18 (1.11–1.26)). In post hoc analyses, results were more consistent for those who already had 3 of 3 baseline years of use, and in patients using nasal inhaler in the latest pollen season (0–2 years, OR 0.76 (0.72–0.79); 3–5 years OR 0.86 (0.81–0.93); 6–9 years, OR 0.94 (0.87–1.02); 10–18 years, OR 0.94 (0.86–1.04)) as opposed to no such use. Conclusions: Patients treated with pollen AIT in routine care to a higher degree stopped using anti-allergic nasal inhaler 0–5 years after starting the standard 3 years of therapy, and not beyond 5 years. Post hoc analyses suggested effectiveness was more consistent among patients with persistent AR.

Background To compare the intrinsic virulence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron variant with the delta variant in hospitalized adults with coronavirus disease 2019 (COVID-19). Methods All adults hospitalized in the Capital Region of Copenhagen with a positive reverse transcription polymerase chain reaction test for SARS-CoV-2 and an available variant determination from 1 September 2021 to 11 February 2022. Data from health registries and patient files were used. Omicron and Delta patients were matched (1:1) by age, sex, comorbidities, and vaccination status. We calculated crude and adjusted hazard ratios (aHRs) for severe hypoxemia and mortality at 30 and 60 days. Results 1,043 patients were included. Patients with Omicron were older, had more comorbidities, were frailer, and more often had three vaccine doses than those with Delta. Fewer patients with Omicron developed severe hypoxemia than those with Delta (aHR, 0.55; 95% confidence interval, 0.38 0.78). Omicron patients exhibited decreased aHR for 30- day mortality compared to Delta (aHR, 0.61; 0.39 0.95). Omicron patients who had received three vaccine doses had lower mortality compared to Delta patients who received three doses (aHR, 0.31;0.16 0.59), but not among those who received two or 0 1 doses (aHR, 0.86; 0.41 1.84 and 0.94; 0.49 1.81 respectively). Similar findings were observed for mortality at 60 days. Similar outcomes were obtained in the analyses of 316 individually matched patients. Conclusions Among adults hospitalized with COVID-19, those with Omicron had less severe hypoxemia and nearly 40% higher 30- and 60-day survival, as compared with those with Delta, mainly driven by a larger proportion of Omicron patients vaccinated with three doses of an mRNA vaccine.

Background Estimates of immunity and severity for the SARS-CoV-2 omicron subvariant BA.5 are important to assess the public health impact associated with its rapid global spread despite vaccination. We estimated natural and vaccine immunity and severity of BA.5 relative to BA.2 in Denmark, a country with high mRNA-vaccination coverage and free-of-charge RT-PCR testing. Methods This nation-wide population-based study in Denmark included residents aged 18 years or older who had taken an RT-PCR test between 10 April and 30 June, 2022 (ie, the outcome period), and who the national COVID-19 surveillance system identified as having information since February 2020 on RT-PCR tests, whole-genome sequencing, vaccinations, and hospitalisation with a positive RT-PCR test and COVID-19 as the main diagnosis. First, we used a case–control design, in which cases were people infected with BA.5 or BA.2 during the outcome period and controls were people who tested negative for SARS-CoV-2 infection during the outcome period. We calculated the protection provided by a previous PCR-confirmed omicron infection against BA.5 and BA.2 infection and hospitalisation among triple-vaccinated individuals. Second, we compared vaccination status in people infected with BA.5 versus BA.2 and estimated relative vaccine protection against each subvariant. Third, we compared rates of hospitalisation for COVID-19 among people infected with BA.5 versus BA.2. We estimated effects using logistic regression with adjustment for sex, age, region, PCR-test date, comorbidity and, as appropriate, vaccination and previous infection status. Findings A total of 210 (2·4%) of 8678 of BA.5 cases, 192 (0·7%) of 29 292 of BA.2 cases, and 33 972 (19·0%) of 178 669 PCR-negative controls previously had an omicron infection, which was estimated in the adjusted analyses to offer 92·7% (95% CI 91·6–93·7) protection against BA.5 infection and 97·1% (96·6–97·5) protection against BA.2 infection. We, BACKGROUND: Estimates of immunity and severity for the SARS-CoV-2 omicron subvariant BA.5 are important to assess the public health impact associated with its rapid global spread despite vaccination. We estimated natural and vaccine immunity and severity of BA.5 relative to BA.2 in Denmark, a country with high mRNA-vaccination coverage and free-of-charge RT-PCR testing.METHODS: This nation-wide population-based study in Denmark included residents aged 18 years or older who had taken an RT-PCR test between 10 April and 30 June, 2022 (ie, the outcome period), and who the national COVID-19 surveillance system identified as having information since February 2020 on RT-PCR tests, whole-genome sequencing, vaccinations, and hospitalisation with a positive RT-PCR test and COVID-19 as the main diagnosis. First, we used a case-control design, in which cases were people infected with BA.5 or BA.2 during the outcome period and controls were people who tested negative for SARS-CoV-2 infection during the outcome period. We calculated the protection provided by a previous PCR-confirmed omicron infection against BA.5 and BA.2 infection and hospitalisation among triple-vaccinated individuals. Second, we compared vaccination status in people infected with BA.5 versus BA.2 and estimated relative vaccine protection against each subvariant. Third, we compared rates of hospitalisation for COVID-19 among people infected with BA.5 versus BA.2. We estimated effects using logistic regression with adjustment for sex, age, region, PCR-test date, comorbidity and, as appropriate, vaccination and previous infection status.FINDINGS: A total of 210 (2·4%) of 8678 of BA.5 cases, 192 (0·7%) of 29 292 of BA.2 cases, and 33 972 (19·0%) of 178 669 PCR-negative controls previously had an omicron infection, which was estimated in the adjusted analyses to offer 92·7% (95% CI 91·6-93·7) protection against BA.5 infection and 97·1% (96·6-97·5) protection against BA.2 infection. We found simil

Excess mortality is an important metric summarising COVID-19 disease burden, informing public health policy and future preparedness needs.1 However, separating the deaths that occurred from COVID-19 versus those from all other causes is challenging. Essentially, the unknowns are the counterfactual, should an infection wave not have happened. A solution to this challenge is to estimate expected number of individuals who would have died and compare this with the observed number of deaths. The estimation of expected number of deaths must consider changes in population and seasonal dynamics and be based on an appropriate reference period. The COVID-19 Excess Mortality Collaborators2 present an important study that estimates 18·2 million excess deaths spread across 191 countries and territories in the first 2 years of the COVID-19 pandemic, 2020 and 2021. The authors use an ensemble-based approach to estimate global excess mortality due to data paucity in many countries. Although this global estimate might be broadly correct and serves as an important reminder of the effect of COVID-19, we strongly caution against the over-interpretation of the constituent country estimates. For European countries, we instead recommend the use of EuroMOMO—a standard and coordinated approach for mortality monitoring in Europe. EuroMOMO estimates expected excess mortality, correcting for delay in registration and changes in population and seasonality during a 5-year reference period.3 EuroMOMO excess mortality estimates include both surplus and deficit mortality, with deficit mortality expected under stringent control restrictions. Whether the COVID-19 Excess Mortality Collaborators2 consider both surplus and deficit mortality is unclear.

Background: The level of protection after a SARS-CoV-2 infection against reinfection and COVID-19 disease remains important with much of the world still unvaccinated. Methods: Analysing nationwide, individually referable, Danish register data including RT-PCR-test results, we conducted a cohort study using Cox regression to compare SARS-CoV-2 infection rates before and after a primary infection among still unvaccinated individuals, adjusting for sex, age, comorbidity and residency region. Estimates of protection against infection were calculated as 1 minus the hazard ratio. Estimates of protection against symptomatic infections and infections leading to hospitalisation were also calculated. The prevalence of infections classified as symptomatic or asymptomatic was compared for primary infections and reinfections. The study also assessed protection against each of the main viral variants after a primary infection with an earlier variant by restricting follow-up time to distinct, mutually exclusive periods during which each variant dominated. Findings: Until 1 July 2021 the estimated protection against reinfection was 83.4% (95%CI: 82.2–84.6%); but lower for the 65+ year-olds (72.2%; 95%CI: 53.2–81.0%). Moderately higher estimates were found for protection against symptomatic disease, 88.3% overall (95%CI: 85.9–90.3%). First-time cases who reported no symptoms were more likely to experience a reinfection (odds ratio: 1.48; 95%CI: 1.35–1.62). By autumn 2021, when infections were almost exclusively caused by the Delta variant, the estimated protection following a recent first infection was 91.3% (95%CI: 89.7–92.7%) compared to 71.4% (95%CI: 66.9–75.3%) after a first infection over a year earlier. With Omicron, a first infection with an earlier variant in the past 3-6 months gave an estimated 51.0% (95%CI: 50.1–52.0%) protection, whereas a first infection longer than 12 months earlier provided only 19.0% (95%CI: 17.2–20.5%) protection. Protection by an earlier variant

Background: Estimates of the severity of the SARS-CoV-2 omicron variant (B.1.1.529) are crucial to assess the public health impact associated with its rapid global dissemination. We estimated the risk of SARS-CoV-2-related hospitalisations after infection with omicron compared with the delta variant (B.1.617.2) in Denmark, a country with high mRNA vaccination coverage and extensive free-of-charge PCR testing capacity. Methods: In this observational cohort study, we included all RT-PCR-confirmed cases of SARS-CoV-2 infection in Denmark, with samples taken between Nov 21 (date of first omicron-positive sample) and Dec 19, 2021. Individuals were identified in the national COVID-19 surveillance system database, which included results of a variant-specific RT-PCR that detected omicron cases, and data on SARS-CoV-2-related hospitalisations (primary outcome of the study). We calculated the risk ratio (RR) of hospitalisation after infection with omicron compared with delta, overall and stratified by vaccination status, in a Poisson regression model with robust SEs, adjusted a priori for reinfection status, sex, age, region, comorbidities, and time period. Findings: Between Nov 21 and Dec 19, 2021, among the 188 980 individuals with SARS-CoV-2 infection, 38 669 (20·5%) had the omicron variant. SARS-CoV-2-related hospitalisations and omicron cases increased during the study period. Overall, 124 313 (65·8%) of 188 980 individuals were vaccinated, and vaccination was associated with a lower risk of hospitalisation (adjusted RR 0·24, 95% CI 0·22–0·26) compared with cases with no doses or only one dose of vaccine. Compared with delta infection, omicron infection was associated with an adjusted RR of hospitalisation of 0·64 (95% CI 0·56–0·75; 222 [0·6%] of 38 669 omicron cases admitted to hospital vs 2213 [1·5%] of 150 311 delta cases). For a similar comparison by vaccination status, the RR of hospitalisation was 0·57 (0·44–0·75) among cases with no or only one dose of vaccine

Following emergence of the SARS-CoV-2 variant Omicron in November 2021, the dominant BA.1 sub-lineage was replaced by the BA.2 sub-lineage in Denmark. We analysed the first 2,623 BA.2 cases from 29 November 2021 to 2 January 2022. No epidemiological or clinical differences were found between individuals infected with BA.1 versus BA.2. Phylogenetic analyses showed a geographic east-to-west transmission of BA.2 from the Capital Region with clusters expanding after the Christmas holidays. Mutational analysis shows distinct differences between BA.1 and BA.2.