Vaccine effectiveness against SARS-CoV-2 infection or COVID-19 hospitalization with the Alpha, Delta, or Omicron SARS-CoV-2 variant: A nationwide Danish cohort study.

BACKGROUND: The continued occurrence of more contagious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants and waning immunity over time require ongoing reevaluation of the vaccine effectiveness (VE). This study aimed to estimate the effectiveness in 2 age groups (12 to 59 and 60 years or above) of 2 or 3 vaccine doses (BNT162b2 mRNA or mRNA-1273) by time since vaccination against SARS-CoV-2 infection and Coronavirus Disease 2019 (COVID-19) hospitalization in an Alpha-, Delta-, or Omicron-dominated period. METHODS AND FINDINGS: A Danish nationwide cohort study design was used to estimate VE against SARS-CoV-2 infection and COVID-19 hospitalization with the Alpha, Delta, or Omicron variant. Information was obtained from nationwide registries and linked using a unique personal identification number. The study included all previously uninfected residents in Denmark aged 12 years or above (18 years or above for the analysis of 3 doses) in the Alpha (February 20 to June 15, 2021), Delta (July 4 to November 20, 2021), and Omicron (December 21, 2021 to January 31, 2022) dominated periods. VE estimates including 95% confidence intervals (CIs) were calculated (1-hazard ratio∙100) using Cox proportional hazard regression models with underlying calendar time and adjustments for age, sex, comorbidity, and geographical region. Vaccination status was included as a time-varying exposure. In the oldest age group, VE against infection after 2 doses was 90.7% (95% CI: 88.2; 92.7) for the Alpha variant, 82.3% (95% CI: 75.5; 87.2) for the Delta variant, and 39.9% (95% CI: 26.3; 50.9) for the Omicron variant 14 to 30 days since vaccination. The VE waned over time and was 73.2% (Alpha, 95% CI: 57.1; 83.3), 50.0% (Delta, 95% CI: 46.7; 53.0), and 4.4% (Omicron, 95% CI: -0.1; 8.7) >120 days since vaccination. Higher estimates were observed after the third dose with VE estimates against infection of 86.1% (Delta, 95% CI: 83.3; 88.4) and 57.7% (Omicron, 95% CI: 55.9; 59.5) 14 to 30 days since vaccination. Among both age groups, VE against COVID-19 hospitalization 14 to 30 days since vaccination with 2 or 3 doses was 98.1% or above for the Alpha and Delta variants. Among both age groups, VE against COVID-19 hospitalization 14 to 30 days since vaccination with 2 or 3 doses was 95.5% or above for the Omicron variant. The main limitation of this study is the nonrandomized study design including potential differences between the unvaccinated (reference group) and vaccinated individuals. CONCLUSIONS: Two vaccine doses provided high protection against SARS-CoV-2 infection and COVID-19 hospitalization with the Alpha and Delta variants with protection, notably against infection, waning over time. Two vaccine doses provided only limited and short-lived protection against SARS-CoV-2 infection with Omicron. However, the protection against COVID-19 hospitalization following Omicron SARS-CoV-2 infection was higher. The third vaccine dose substantially increased the level and duration of protection against infection with the Omicron variant and provided a high level of sustained protection against COVID-19 hospitalization among the +60-year-olds

Relative vaccine protection, disease severity, and symptoms associated with the SARS-CoV-2 omicron subvariant BA.2.86 and descendant JN.1 in Denmark: a nationwide observational study

BACKGROUND: During the 2023 Danish COVID-19 vaccination campaign, an updated monovalent mRNA vaccine targeting the SARS-CoV-2 omicron XBB.1.5 subvariant was administered. However, the rapid spread of a genetically divergent omicron BA.2.86 subvariant, JN.1, since September, 2023, poses potential challenges due to its rapid dominance and possible immune escape. Using national electronic health registry data from all regions of Denmark, we aimed to investigate whether the SARS-CoV-2 subvariant BA.2.86, and its descendant JN.1, differed from other circulating variants in terms of their ability to escape vaccine protection, the risk of infection leading to severe disease, and self-reported symptoms among infected people. METHODS: In this observational study, we included all residents of Denmark aged 65 years and older who tested positive for SARS-CoV-2 by PCR between Oct 1 and Dec 31, 2023, and for whom genomic data on the SARS-CoV-2 variant that had caused their infection were available. Data from clinical testing, sentinel, and self-sampling-based surveillance were linked with national electronic civil, vaccination, and hospitalisation registers. The relative protection of the XBB.1.5 updated COVID-19 vaccine against BA.2.86 infections versus infections with other variants was analysed in a case-only study, and the relative risk of hospitalisation in people infected with BA.2.86 versus other variants was analysed in a case-control study. Both analyses were adjusted for time, comorbidities, and previous vaccination history, among other potential confounders. Additionally, prevalence patterns in self-reported symptoms among people of all ages infected with SARS-CoV-2 were reported separately by subvariant. FINDINGS: Of the 7581 people in Denmark aged 65 years or older who tested positive for SARS-CoV-2 by PCR during the study period, 5882 (78%) samples were eligible for sequencing. 3862 (66%) of these passed quality control, were successfully sequenced, and the SARS-CoV-2 variant and subvariant identified, and these individuals were included in the study. Of these 3862 people, 2184 (57%) were infected with the BA.2.86 subvariant, including 1615 JN.1 infections. Participants infected with BA.2.86 had 1·52 (95% CI 1·25-1·86) times the odds, and those infected with JN.1 had 1·60 (1·27-2·02) times the odds, of having received the XBB.1.5 vaccine at least 7 days before their infection compared with participants infected with a non-BA.2.86 variant. The severity analysis showed no evidence of association between the infecting variant and the risk of COVID-19 hospitalisation (odds ratio 1·04 [95% CI 0·86-1·26] for BA.2.86 and 1·07 [0·85-1·34] for JN.1). Similarly, there was no evidence of differences in self-reported symptoms by variant strain. INTERPRETATION: Compared with other SARS-CoV-2 variants, BA.2.86 and the JN.1 sublineage were less sensitive to vaccine-induced immune protection from the XBB.1.5 updated COVID-19 vaccine; however, we found no evidence that infection with BA.2.86 or JN.1 resulted in increased disease severity or different symptom profiles. Although less effective against the new variants, XBB.1.5 vaccination remains protective and reduces the risk of infection and COVID-19 disease. FUNDING: The Danish Government and the EU's EU4Health programme

Risk of Pharmacological or Hospital Treatment for Depression in Patients with Colorectal Cancer–Associations with Pre-Cancer Lifestyle, Comorbidity and Clinical Factors

We investigated the risk of depression in colorectal cancer (CRC) patients and associated risk factors. The 1324 patients with CRC and 6620 matched cancer-free participants from the Diet, Cancer and Health study were followed for up to 16 years for either a first hospitalization for depression or antidepressant prescription after diagnosis of CRC cancer or study entry date. Information on the outcome and covariates was retrieved from the Danish Colorectal Cancer Group database, the national health registries and questionnaires. Cumulative incidence of depression was estimated, and Cox regression models were used to evaluate the association between risk factors and depression incidence. During follow-up, 191 (14.4%) patients with CRC and 175 (2.6%) cancer-free comparison persons experienced depression. After adjustments, in the first year after cancer diagnosis, patients with CRC had a 12-fold higher hazard compared with the cancer-free population (HR, 12.01; 95% CI, 7.89–18.28). The risk decreased during follow-up but remained significantly elevated with an HR of 2.65 (95% CI, 1.61–4.36) after five years. Identified risk factors were presence of comorbidities, advanced disease stage and use of radiotherapy, while life style factors (pre-cancer or at diagnosis) and chemotherapy did not seem to contribute to the increased risk

Vaccine effectiveness against SARS-CoV-2 reinfection during periods of Alpha, Delta, or Omicron dominance: A Danish nationwide study.

BackgroundIndividuals with a prior Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection have a moderate to high degree of protection against reinfection, though seemingly less so when the Omicron variant of SARS-CoV-2 started to circulate. The aim of this study was to evaluate the vaccine effectiveness (VE) against SARS-CoV-2 reinfection, Coronavirus Disease 2019 (COVID-19)-related hospitalization, and COVID-19-related death, in individuals with prior SARS-CoV-2 infection, and to assess the effect of time since vaccination during periods with different dominant SARS-CoV-2 variants.Methods and findingsThis study used a nationwide cohort design including all individuals with a confirmed SARS-CoV-2 infection, who were alive, and residing in Denmark between 1 January 2020 and 31 January 2022. Using Danish nationwide registries, we obtained information on SARS-CoV-2 infections, COVID-19 vaccination, age, sex, comorbidity, staying at hospital, and country of origin. The study population included were individuals with prior SARS-CoV-2 infection. Estimates of VE against SARS-CoV-2 reinfection with 95% confidence intervals (CIs) were calculated using a Poisson regression model and adjusted for age, sex, country of origin, comorbidity, staying at hospital, calendar time, and test incidence using a Cox regression model. The VE estimates were calculated separately for three periods with different dominant SARS-CoV-2 variants (Alpha (B.1.1.7), Delta (B.1.617.2), or Omicron (B.1.1.529)) and by time since vaccination using unvaccinated as the reference. In total, 148,527 person-years and 44,192 SARS-CoV-2 infections were included for the analysis regarding reinfections. The study population comprised of 209,814 individuals infected before or during the Alpha period, 292,978 before or during the Delta period, and 245,530 before or during the Omicron period. Of these, 40,281 individuals had completed their primary vaccination series during the Alpha period (19.2%), 190,026 during the Delta period (64.9%), and 158,563 during the Omicron period (64.6%). VE against reinfection following any COVID-19 vaccine type administered in Denmark, peaked at 71% (95% CI: -Inf to 100%) at 104 days or more after vaccination during the Alpha period, 94% (95% CI: 92% to 96%) 14 to 43 days after vaccination during the Delta period, and 60% (95% CI: 58% to 62%) 14 to 43 days after vaccination during the Omicron period. Waning immunity following vaccination was observed and was most pronounced during the Omicron period. Due to too few events, it was not possible to estimate VE for hospitalization and death. Study limitations include potentially undetected reinfections, differences in health-seeking behavior, or risk behavior between the compared groups.ConclusionsThis study shows that in previously infected individuals, completing a primary vaccination series was associated with a significant protection against SARS-CoV-2 reinfection compared with no vaccination. Even though vaccination seems to protect to a lesser degree against reinfection with the Omicron variant, these findings are of public health relevance as they show that previously infected individuals still benefit from COVID-19 vaccination in all three variant periods

Vaccine effectiveness against SARS-CoV-2 reinfection during periods of Alpha, Delta, or Omicron dominance: A Danish nationwide study

BACKGROUND: Individuals with a prior Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection have a moderate to high degree of protection against reinfection, though seemingly less so when the Omicron variant of SARS-CoV-2 started to circulate. The aim of this study was to evaluate the vaccine effectiveness (VE) against SARS-CoV-2 reinfection, Coronavirus Disease 2019 (COVID-19)-related hospitalization, and COVID-19-related death, in individuals with prior SARS-CoV-2 infection, and to assess the effect of time since vaccination during periods with different dominant SARS-CoV-2 variants. METHODS AND FINDINGS: This study used a nationwide cohort design including all individuals with a confirmed SARS-CoV-2 infection, who were alive, and residing in Denmark between 1 January 2020 and 31 January 2022. Using Danish nationwide registries, we obtained information on SARS-CoV-2 infections, COVID-19 vaccination, age, sex, comorbidity, staying at hospital, and country of origin. The study population included were individuals with prior SARS-CoV-2 infection. Estimates of VE against SARS-CoV-2 reinfection with 95% confidence intervals (CIs) were calculated using a Poisson regression model and adjusted for age, sex, country of origin, comorbidity, staying at hospital, calendar time, and test incidence using a Cox regression model. The VE estimates were calculated separately for three periods with different dominant SARS-CoV-2 variants (Alpha (B.1.1.7), Delta (B.1.617.2), or Omicron (B.1.1.529)) and by time since vaccination using unvaccinated as the reference. In total, 148,527 person-years and 44,192 SARS-CoV-2 infections were included for the analysis regarding reinfections. The study population comprised of 209,814 individuals infected before or during the Alpha period, 292,978 before or during the Delta period, and 245,530 before or during the Omicron period. Of these, 40,281 individuals had completed their primary vaccination series during the Alpha period (19.2%), 190,026 during the Delta period (64.9%), and 158,563 during the Omicron period (64.6%). VE against reinfection following any COVID-19 vaccine type administered in Denmark, peaked at 71% (95% CI: -Inf to 100%) at 104 days or more after vaccination during the Alpha period, 94% (95% CI: 92% to 96%) 14 to 43 days after vaccination during the Delta period, and 60% (95% CI: 58% to 62%) 14 to 43 days after vaccination during the Omicron period. Waning immunity following vaccination was observed and was most pronounced during the Omicron period. Due to too few events, it was not possible to estimate VE for hospitalization and death. Study limitations include potentially undetected reinfections, differences in health-seeking behavior, or risk behavior between the compared groups. CONCLUSIONS: This study shows that in previously infected individuals, completing a primary vaccination series was associated with a significant protection against SARS-CoV-2 reinfection compared with no vaccination. Even though vaccination seems to protect to a lesser degree against reinfection with the Omicron variant, these findings are of public health relevance as they show that previously infected individuals still benefit from COVID-19 vaccination in all three variant periods

Crude vaccine effectiveness against SARS-CoV-2 reinfection during periods of Alpha, Delta, or Omicron dominance.

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Checklist of items that should be included in reports of <i>cohort studies</i>.

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Adjusted VE against SARS-CoV-2 reinfection during periods of Alpha, Delta, or Omicron dominance.

(A) Alpha variant (B.1.1.7), 20 February–15 June 2021. (B) Delta variant (B.1.617.2), 4 July–20 November 2021. (C) Omicron variant (B.1.1.529), 21 December 2021–31 January 2022. VE adjusted for age, sex, country of origin, comorbidity, staying at hospital, calendar time, and test incidence. CI, confidence interval; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2; VE, vaccine effectiveness.</p

Adjusted VE against SARS-CoV-2 reinfection during periods of Alpha, Delta, or Omicron dominance.

Adjusted VE against SARS-CoV-2 reinfection during periods of Alpha, Delta, or Omicron dominance.</p

Definition of country of origin.

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