The effectiveness of COVID-19 vaccination against the risk of SARS-CoV-2 infection, hospitalization, and death wanes progressively over 9 months, but the rate of waning varies according to the type of vaccine, according to research recently published in the Lancet.

Researchers conducted a retrospective, total population cohort study in Sweden, sourcing data for a total of 1,685,948 individuals from Swedish nationwide registers. All individuals immunized with 2 doses of any COVID-19 vaccine (ChAdOx1 nCoV-19, mRNA-1273, or BNT162b2; n = 842,974) and all individuals with a recorded SARS-CoV-2 infection were matched by birth year, sex, and municipality to the same number of nonimmunized individuals. Data from all participants were assessed for 2 outcomes: (1) SARS-CoV-2 infection of any severity from January 12 to October 4, 2021 and (2) severe COVID-19, described as hospitalization for COVID-19 or death from any cause within 30 days of confirmed infection from March 15 to September 28, 2021.

Vaccine effectiveness declined  progressively for all vaccines types during follow-up, but waning occurred at different speeds. For SARS-CoV-2 infection of any severity, the vaccine effectiveness of BNT162b2 diminished progressively over time, from 92% (95% CI, 92-93; P <.001) at 15-30 days, to 47% (95% CI, 39-55; P <.001) at 121-180 days, and to 23% (95% CI, -2 to 41; P =.07) from day 211 onward. Effectiveness declined slightly more slowly for mRNA-1273, which had a vaccine effectiveness of 96% (95% CI, 94-97; P <.001) at 15-30 days and 59% (95% CI, 18-79; P = .012) from day 181 on. Waning also was slightly slower for heterologous ChAdOx1 nCoV-19 plus an mRNA vaccine, for which vaccine effectiveness was 89% (95% CI, 79-94; P <.001) at 15-30 days and 66% (95% CI, 41-80; P <.001) from day 121 on. In contrast, vaccine effectiveness for homologous ChAdOx1 nCoV-19 vaccine was 68% (95% CI, 52-79; P <.001) at 15-30 days, with no demonstrable effectiveness from day 121 onward (95% CI, -19% [-98 to 28]; P =.49). When examining the outcome of severe COVID-19, vaccine effectiveness waned from 89% (95% CI, 82-93; P <.001) at 15-30 days to 64% (95% CI, 44 to 77; P <.001) from day 121 forward.


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Generally, some evidence showed lower vaccine effectiveness in men than in women and in older individuals than in younger ones. No detectable vaccine effectiveness was observed in men (17%; [95% CI, -13 to 40]; P =.23) from day 181 onward, whereas it endured in women (34%; [95% CI, 22-45]; P <.001). At 61-120 days, vaccine effectiveness waned to 50% (95% CI, 30-64; P <.001) in those 80 years or older.

In sensitivity analyses, the data confirmed declining vaccine effectiveness for SARS-CoV-2 infection of any severity, including the different rate of waning for different vaccine schedules. This analysis also confirmed that vaccine effectiveness upheld better against the outcome of severe COVID-19 than against SARS-CoV-2 infection of any severity, although some waning was seen after 4 months.

The study was limited by the possibility of residual and unmeasured confounding, including a greater risk of selection bias in unvaccinated individuals with longer follow-up time. It also is likely that some participants with a prior asymptomatic infection were included in the analyses.

“The results of our study have important clinical implications, as they strengthen the evidence-based rationale for administration of a third vaccine dose as a booster, especially to specific high-risk populations,” the investigators wrote.

Reference

Nordström P, Ballin M, Nordström A. Risk of infection, hospitalisation, and death up to 9 months after a second dose of COVID-19 vaccine: a retrospective, total population cohort study in Sweden. Lancet. Published online February 4, 2022. doi:10.1016/S0140-6736(22)00089-7

This article originally appeared on Pulmonology Advisor