ABSTRACT
ObjectiveTo 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. DesignPopulation-based cohort analyses. SettingDenmark, Finland, Norway, and Sweden, 27 December 2020 to 28 February 2022. ParticipantsAdults 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 measuresUsing 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. ResultsHeterologous 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. ConclusionHeterologous 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.
ABSTRACT
BackgroundThe elderly are highly vulnerable to severe Covid-19. Waning immunity and emergence of Omicron have caused concerns about reduced effectiveness of Covid-19 vaccines. The objective was to estimate vaccine effectiveness (VE) against severe Covid-19 among the elderly. MethodsThis nationwide, register-based cohort analysis included all residents aged 70 years and over in Finland. The follow-up started on December 27, 2020, and ended on March 31, 2022. The outcomes of interest were Covid-19-related hospitalization and intensive care unit (ICU) admission timely associated with SARS-CoV-2 infection. VE was estimated as one minus the hazard ratio comparing the vaccinated and unvaccinated and taking into account time since vaccination. Omicron-specific VE was evaluated as the effectiveness observed since January 1, 2022. ResultsThe cohort included 896220 individuals. Comirnaty (BioNTech/Pfizer) VE against Covid-19-related hospitalization was 93% (95% CI 89%-95%) and 85% (95% CI 82%-87%) 14-90 and 91-180 days after the second dose; VE increased to 95% (95% CI 94%-96%) 14-60 days after the third dose. VE of other homologous and heterologous three dose series was similar. Protection against severe Covid-19 requiring ICU treatment was even better. Since January 1, 2022, Comirnaty VE was 98% (95% CI 92%-99%) and 92% (95% CI 87%-95%) 14-90 and 91-180 days after the second and 98% (95% CI 95%-99%) 14-60 days after the third dose. ConclusionsVE against severe Covid-19 is high among the elderly. It waned slightly after two doses, but a third restored the protection. VE against severe Covid-19 remained high even after the emergence of Omicron.
ABSTRACT
Recently, Covid-19 vaccine effectiveness has decreased especially against mild disease due to emergence of the Delta variant and waning protection. In this register-based study among healthcare workers in Finland, the vaccine effectiveness of two-dose mRNA vaccine series against SARS-CoV-2 infection decreased from 82% (95% CI 79-85%) 14-90 days after vaccination to 53% (43-62%) after 6 months. Similar trend was observed for other series. Waning was not observed against Covid-19 hospitalization. These results facilitate decision-making of booster doses for healthcare workers.
ABSTRACT
IntroductionThe aim of this study was to investigate how age and underlying medical conditions affect the risk of severe outcomes following SARS-CoV-2 infection and how they should be weighed while prioritising vaccinations against COVID-19. MethodsThis population-based register study includes all SARS-CoV-2 PCR-test-positive cases until 24 Feb 2021, based on the Finnish National Infectious Diseases Register. The cases were linked to other registers to identify presence of comorbidities and severe outcomes (hospitalisation, intensive care treatment, death). The odds of severe outcomes were compared in those with and without the pre-specified comorbidities using logistic regression. Furthermore, population-based rates were compared between those with a given comorbidity and those without any of the specified comorbidities using negative binomial regression. ResultsAge and various comorbidities were found to be predictors of severe COVID-19. Compared to 60-69-year-olds, the odds ratio (OR) of death was 7.1 for 70-79-year-olds, 26.7 for 80-89-year-olds, and 55.8 for [≥]90-year-olds. Among the 20-69-year-olds, chronic renal disease (OR 9.4), malignant neoplasms (5.8), hematologic malignancy (5.6), chronic pulmonary disease (5.4), and cerebral palsy or other paralytic syndromes (4.6) were strongly associated with COVID-19 mortality; severe disorders of the immune system (8.0), organ or stem cell transplant (7.2), chronic renal disease (6.7), and diseases of myoneural junction and muscle (5.5) were strongly associated with COVID-19 hospitalisation. Type 2 diabetes and asthma, two very common comorbidities, were associated with all three outcomes, with ORs from 2.1 to 4.3. The population-based rate of SARS-CoV-2 infection decreased with age. Taking the 60-69-year-olds as reference, the rate ratio was highest (3.0) for 20-29-year-olds but <1 for 70-79-year-olds and 80-89-year-olds. ConclusionComorbidities predispose for severe COVID-19 among younger ages. In vaccine prioritisation both the risk of infection and the risk of severe outcomes, if infected, should be combined.
ABSTRACT
BackgroundIn Finland, both mRNA and adenovirus vector (AdV) Covid-19 vaccines have been used after the vaccination campaign started on December 27, 2020. Vaccination of the elderly and chronically ill was prioritized and the interval between doses set to 12 weeks. The objective of this interim analysis was to evaluate first and second dose vaccine effectiveness (VE) in a real-world setting. MethodsDuring the first 5 months of the campaign, a register-based cohort study was conducted in the Finnish elderly aged 70+ years and those aged 16-69 years with medical conditions predisposing to severe Covid-19 (chronically ill). Using Cox regression, VE against SARS-CoV-2 infection and Covid-19 hospitalization was estimated comparing the hazard in the vaccinated with that in the unvaccinated. ResultsThe cohorts included 901092 elderly (89% vaccinated) and 774526 chronically ill (69% vaccinated) individuals. Three weeks after the first dose, mRNA VE against infection was 45% (95% confidence interval, 36-53%) and 40% (26-51%) in elderly and chronically ill; mRNA VE against hospitalization was 63% (49-74%) and 82% (56-93%). In chronically ill, AdV VE was 42% (32-50) and 62% (42- 75%) against infection and hospitalization, respectively. One week after the second dose, mRNA VE against infection was 75% (65-82%) and 77% (65-85%) in elderly and chronically ill; mRNA VE against hospitalization was 93% (70-98%) and 90% (29-99%). ConclusionsCovid-19 vaccines protect against SARS-CoV-2 infection and Covid-19 hospitalization. A single dose provides moderate protection in elderly and chronically ill, although 2 doses are clearly superior. summaryThis register-based cohort study demonstrates that Covid-19 vaccines protect against SARS-CoV-2 infection and Covid-19 hospitalization among Finnish elderly and chronically ill. Vaccine effectiveness against hospitalization was moderate after 1 dose and increased to [≥]90% after 2 doses.
