SARS-CoV-2 infection and post-acute risk of non-Covid-19 infectious disease hospitalizations: a nationwide cohort study of Danish adults aged >=50 years (preprint)

Reports suggest that the potential long-lasting health consequences of SARS-CoV-2 infection may involve persistent dysregulation of some immune populations, but the potential clinical implications are unknown. In a nationwide cohort of 2,430,694 50+-year-olds, we compared the rates of non-Covid-19 infectious disease inpatient hospitalizations (of [≥]5 hours) following the acute phase of SARS-CoV-2 infection in 930,071 individuals with rates among SARS-CoV-2 uninfected from 1 January 2021 to 10 December 2022. The post-acute phase of SARS-CoV-2 infection was associated with an incidence rate ratio of 0.90 (95% confidence interval 0.88-0.92) for any infectious disease hospitalization. Findings were similar for upper- (1.08, 0.97-1.20), lower respiratory tract (0.90, 0.87-0.93), influenza (1.04, 0.94-1.15), gastrointestinal (1.28, 0.78-2.09), skin (0.98, 0.93-1.03), urinary tract (1.01, 0.96-1.08), certain invasive bacterial (0.96, 0.91-0.1.01), and other (0.96, 0.92-1.00) infectious disease hospitalizations and in subgroups. Our study does not support an increased susceptibility to non-Covid-19 infectious disease hospitalization following SARS-CoV-2 infection.

Safety of bivalent omicron-containing mRNA-booster vaccines: a nationwide cohort study (preprint)

Background: Safety data to support bivalent omicron-containing mRNA-booster vaccination are lacking. Methods: In a Danish nationwide cohort study from 1 January 2021 to 10 December 2022, we examined the association between bivalent omicron-containing mRNA-booster vaccination as a fourth Covid-19 vaccine dose and risk of adverse events in individuals aged [≥]50 years. Using incidence rate ratios estimated with Poisson regression, we compared the rates of hospital visits for 27 different adverse events in a 28-day main risk period following vaccination with a bivalent omicron-containing mRNA-booster vaccine as a fourth dose to reference period rates from day 29 after the third or fourth vaccine dose and onward. Secondary analyses included stratifying by sex, age, and vaccine type and assessing the associations using self-controlled case series and observed vs. expected cohort analyses. Results: 1,740,417 individuals (mean age 67.8 years, standard deviation 10.7) received a bivalent omicron-containing mRNA-booster vaccine as a fourth dose. Fourth dose vaccination with a bivalent omicron-containing booster did not statistically significantly increase the rate of any of the 27 adverse outcomes within 28 days, nor when analyzed according to age, sex, vaccine type, or using alternative analytical approaches. However, post-hoc analysis detected signals for myocarditis (statistically significantly so in females), although the outcome was very rare and findings were based on few cases. No risk of cerebrovascular infarction was found. Conclusions: Bivalent omicron-containing mRNA-booster vaccination as a fourth dose was not associated with an increased risk of 27 different adverse events in 50+-year-olds.

Comparative effectiveness of the bivalent BA.4-5 and BA.1 mRNA-booster vaccines in the Nordic countries (preprint)

Background: Data on the comparative vaccine effectiveness (CVE) of the bivalent mRNA-booster vaccines containing the original SARS-CoV-2 and omicron BA.4-5 and BA.1 subvariants are limited. Methods: In a period of BA.4-5 subvariants predominance, we estimated the CVE of the bivalent Comirnaty (Pfizer-BioNTech) and Spikevax (Moderna) BA.4-5 and BA.1 mRNA-booster vaccines given as a fourth dose in Denmark, Finland, Norway, and Sweden. From 1 July 2022 to 12 December 2022, we conducted nationwide cohort analyses using target trial emulation to compare risks of Covid-19 hospitalization and death in four-dose (second booster) with three-dose (first booster) vaccinated and between four-dose vaccinated individuals. Results: Compared with having received three vaccine doses, receipt of a bivalent BA.4-5 booster as a fourth dose was associated with a country-combined CVE against Covid-19 hospitalization of 80.5% (95% confidence interval, 69.5% to 91.5%). The corresponding CVE for bivalent BA.1 boosters was 74.0% (68.6% to 79.4%). CVE against Covid-19 death was 77.8% (48.3% to 100%) and 80.1% (72.0% to 88.2%) for bivalent BA.4-5 and BA.1 boosters as a fourth dose, respectively. The CVE of bivalent BA.4-5 vs. BA.1 boosters were 32.3% (10.6% to 53.9%) for Covid-19 hospitalization and 12.3% (-36.1% to 60.7%) for death (the latter estimable in Denmark only). Conclusions: Vaccination with bivalent BA.4-5 or BA.1 mRNA-booster vaccines as a fourth dose was associated with increased protection against Covid-19 hospitalization and death during a period of BA.4-5 predominance. Bivalent BA.4-5 boosters conferred moderately greater vaccine effectiveness against Covid-19 hospitalization compared with bivalent BA.1 boosters.

Comparative effectiveness of heterologous booster schedules with AZD1222, BNT162b2, or mRNA-1273 vaccines against COVID-19 during omicron predominance in the Nordic countries (preprint)

Objective: To investigate the effectiveness of heterologous booster schedules with AZD1222 (Oxford-AstraZeneca, referred to as AZD), BNT162b2 (Pfizer-BioNTech, BNT), and mRNA-1273 (Moderna, MOD) vaccines compared with primary schedules and with homologous mRNA-vaccine booster schedules during a period of omicron predominance. Design: Population-based cohort analyses. Setting: Denmark, Finland, Norway, and Sweden, 27 December 2020 to 28 February 2022. Participants: Adults that had received at least a primary vaccination schedule (ie, two doses) of the AZD, BNT, and/or MOD vaccines during the study period. Main outcome measures: Using the Kaplan-Meier estimator, we compared country-specific risks of SARS-CoV-2 infection and severe COVID-19 outcomes in heterologous booster vaccinated with primary schedule vaccinated (matched analyses) and homologous booster vaccinated (weighted analyses) since emergence of omicron. Results: Heterologous booster schedules improved protection against all outcomes compared with primary schedules, with the largest and most robust effects observed for severe COVID-19. Risk differences for documented infection ranged from -22.4% to -3.1% (comparative vaccine effectiveness [CVE] 9.7% to 60.9%; >63.2% for COVID-19 hospitalisation) across countries for AZD1BNT2BNT3 (AZD as primary dose followed by two doses of BNT) vs AZD1BNT2 and -22.2% to -3.2% (CVE 37.4% to 67.8%; >34.6% for hospitalisation) for BNT1BNT2MOD3 vs BNT1BNT2, the two most common heterologous booster schedules. Heterologous- and homologous booster schedules had comparable effectiveness. Risk differences of documented infection ranged from -0.4% to 4.4% (CVE -20.0% to 2.4%) for AZD1BNT2BNT3 vs BNT1BNT2BNT3 and -19.8% to 1.7% (CVE -14.6% to 53.8%) for BNT1BNT2MOD3 vs BNT1BNT2BNT3; for most comparisons, risk differences for severe COVID-19 outcomes were smaller than 1 per 1000 vaccinated. Previous infection followed by a booster dose conferred the greatest protection. Conclusion: Heterologous booster vaccine schedules are associated with an increased protection against omicron-related COVID-19 outcomes that is comparable to that afforded by homologous booster schedules.