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Effectiveness of Covid-19 Vaccination Against Risk of Symptomatic Infection, Hospitalization, and Death Up to 9 Months: A Swedish Total-Population Cohort Study

34 Pages Posted: 25 Oct 2021

See all articles by Peter Nordström

Peter Nordström

University of Umea - Unit of Geriatric Medicine

Marcel Ballin

University of Umea

Anna Nordström

University of Umea

More...

Abstract

Background: Whether vaccine effectiveness against Coronavirus disease 2019 (Covid-19) lasts longer than 6 months is unclear.

Methods: A retrospective cohort study was conducted using Swedish nationwide registries. The cohort comprised 842,974 pairs (N=1,684,958), including individuals vaccinated with 2 doses of ChAdOx1 nCoV-19, mRNA-1273, or BNT162b2, and matched unvaccinated individuals. Cases of symptomatic infection and severe Covid-19 (hospitalization or 30-day mortality after confirmed infection) were collected from 12 January to 4 October 2021. 

Findings: Vaccine effectiveness of BNT162b2 against infection waned progressively from 92% (95% CI, 92-93, P<0·001) at day 15-30 to 47% (95% CI, 39-55, P<0·001) at day 121-180, and from day 211 and onwards no effectiveness could be detected (23%; 95% CI, -2-41, P=0·07). The effectiveness waned slightly slower for mRNA-1273, being estimated to 59% (95% CI, 18-79) from day 181 and onwards. In contrast, effectiveness of ChAdOx1 nCoV-19 was generally lower and waned faster, with no effectiveness detected from day 121 and onwards (-19%, 95% CI, -97-28), whereas effectiveness from heterologous ChAdOx1 nCoV-19 / mRNA was maintained from 121 days and onwards (66%; 95% CI, 41-80). Overall, vaccine effectiveness was lower and waned faster among men and older individuals. For the outcome severe Covid-19, effectiveness waned from 89% (95% CI, 82-93, P<0·001) at day 15-30 to 42% (95% CI, -35-75, P=0·21) from day 181 and onwards, with sensitivity analyses showing notable waning among men, older frail individuals, and individuals with comorbidities.

Interpretation: Vaccine effectiveness against symptomatic Covid-19 infection wanes progressively over time across all subgroups, but at different rate according to type of vaccine, and faster for men and older frail individuals. The effectiveness against severe illness seems to remain high through 9 months, although not for men, older frail individuals, and individuals with comorbidities. This strengthens the evidence-based rationale for administration of a third booster dose.

Funding: None to declare.

Declaration of Interest: None to declare.

Ethical Approval: This study was approved by the Swedish Ethical Review Authority (number 495/2021)

Keywords: Covid-19 infection, Vaccination

Suggested Citation

Nordström, Peter and Ballin, Marcel and Nordström, Anna, Effectiveness of Covid-19 Vaccination Against Risk of Symptomatic Infection, Hospitalization, and Death Up to 9 Months: A Swedish Total-Population Cohort Study. Available at SSRN: https://ssrn.com/abstract=3949410 or http://dx.doi.org/10.2139/ssrn.3949410

Peter Nordström (Contact Author)

University of Umea - Unit of Geriatric Medicine ( email )

Umea
Sweden

Marcel Ballin

University of Umea ( email )

UNIVERSITETSTORGET 4
907 36 Umeå
Sweden

Anna Nordström

University of Umea ( email )

UNIVERSITETSTORGET 4
907 36 Umeå
Sweden

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