Swedish scientists reveal rapid decline in effectiveness of COVID-19 vaccine when infected with omicron strain

Results of a new Swedish study posted on Preprints with The Lancet showed that two doses of the COVID-19 vaccine provided effective long-term protection against infection, but less protection against the omicron strain (reduction to 43% by week 4 and no protection by week 14). Moreover, two doses of COVID-19 vaccine provided significant long-term protection against severe disease, according to follow-up results up to 13 months after vaccination. 

The purpose of this study was to evaluate the vaccine's time-dependent effectiveness against COVID-19, hospitalization rates, intensive care unit (ICU) admissions, and mortality at 13 months after two doses of COVID-19 vaccination. 

The study compared the time-dependent pattern of vaccination before and after the omicron strain. 

In a cohort of 9,153,456 people, 85% were vaccinated with one dose of COVID-19 vaccine, 82% were vaccinated with two doses of vaccine, 45% were vaccinated with at least three doses of vaccine, and 15% were not vaccinated. The majority of those vaccinated (86%) were 65 years of age or older. 

During the study period, 22% of the study population were newly infected with SARS-CoV-2. There were 0.9% hospitalizations, and 0.1% required ICU admission. The mortality rate was 0.2%. 

Vaccine efficacy among hospitalized individuals reached 90% at weeks 5 and 6 and persisted to 82% from weeks 1 through 25. Meanwhile, efficacy after the second dose was higher and persisted longer. 

The omicron strain caused the fastest drop in vaccine efficacy. Vaccinated individuals who received two doses of COVID-19 failed to maintain protection against omicron for 14 weeks after the second dose.

The efficacy rate of the vaccine against hospitalization in the period before omicron infection was consistent and stable, above 85%. Vaccine efficacy after omicron infection was maintained at 80% until week 25 and declined over time. Nevertheless, limited protection against hospitalization was maintained throughout the study period.

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