Effectiveness of vaccination against SARS-CoV-2 infection and Covid-19 hospitalisation among Finnish elderly and chronically ill—An interim analysis of a nationwide cohort study

Abstract

Background In 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. Methods During the first five 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 hospitalisation was estimated comparing the hazard in the vaccinated with that in the unvaccinated. Results The 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 hospitalisation was 63% (49–74%) and 82% (56–93%). In chronically ill, AdV VE was 42% (32–50) and 62% (42–75%) against infection and hospitalisation, 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 hospitalisation was 93% (70–98%) and 90% (29–99%). Conclusions Covid-19 vaccines protect against SARS-CoV-2 infection and Covid-19 hospitalisation. A single dose provides moderate protection in elderly and chronically ill, although two doses are clearly superior.

High vaccine effectiveness against severe Covid-19 in the elderly in Finland before and after the emergence of Omicron

“…We used the data in the Care Register for Health Care from 2015 onwards to count the number of nights hospitalized between 2015 and 2019 and to assess the presence of comorbidities that predispose to severe Covid-19 according to a recent study of predictors of Covid-19 hospitalization [26]. We completed the collection of data on predisposing comorbidities with primary health care records and prescription data as described in a previous study [3].…”

“…The elderly are highly vulnerable to severe coronavirus disease 2019 (Covid-19) (1) and, therefore, protecting them is essential to reduce the disease burden caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Covid-19 vaccinations prevent SARS-CoV-2 infections and decrease the number of Covid-19 hospitalizations in a population (2)(3)(4)(5)(6)(7).…”

Protective Duration of ChAdOx1 and BNT162b2 Vaccines Against SARS-CoV-2 Infection

“…In comparison, the median protection duration of the primary COVID-19 vaccinations was longer among those aged 60 years and older compared with other age groups (adolescents and adults). Several studies revealed that BNT162b2, Moderna, and ChAdOx1 vaccines’ effectiveness are high among elderly individuals [ 12 , 15 , 16 ]. A common explanation for these outcomes is the priority of vaccine administration among elderly individuals as they are considered a high-risk group for COVID-19, and they could be less exposed to infection by staying at home.…”

Impaired immunity and high attack rates caused by SARS‐CoV‐2 variants among vaccinated long‐term care facility residents

“…Our results and reports from other outbreaks in nursing homes 16,17 confirm the possibility of SARS-CoV-2 spread in nursing homes even when most residents are vaccinated. Others have reported that although vaccine effectiveness (VE) against infection by SARS-CoV-2 variants is remarkably decreased, [18][19][20][21] VE against severe illness remains high after two doses. 18,[21][22][23] Among all infected residents in the two LTFCs four residents died after having tested positive for COVID-19, but only one death was ruled to have been caused by COVID-19 with certainty.…”

“…Others have reported that although vaccine effectiveness (VE) against infection by SARS-CoV-2 variants is remarkably decreased, [18][19][20][21] VE against severe illness remains high after two doses. 18,[21][22][23] Among all infected residents in the two LTFCs four residents died after having tested positive for COVID-19, but only one death was ruled to have been caused by COVID-19 with certainty. Due to our small sample size and deaths with unclear relation to COVID-19 we were unable to assess VE.…”