Post-COVID symptoms after SARS-CoV-2 omicron infection and the effect of booster vaccination: A population-based cohort study

Background: The impact of vaccination on the type and risk of specific post-COVID symptoms after Omicron infection is not clear. We aimed to investigate the excess risk and patterns of 22 symptoms 3-5 months after Omicron infection, comparing uninfected and infected subjects with and without recent booster vaccination. Methods: We conducted a population-based prospective study based on four questionnaire-based cohorts linked to national health registries. Our study includes female and male participants aged 11-80 years from The Norwegian Mother, Father, and Child Cohort Study, The Norwegian Influenza Pregnancy Cohort, The Senior Cohort, and The Young Adult Cohort. All participants registered presence of 22 COVID-related symptoms irrespective of infection and vaccination status. Results: The study sample includes more than 31,000 uninfected and 26,000 Omicron infected subjects. Among infected subjects, 12 % were vaccinated with two doses >130 days before the primary infection (median 154 days) but had not received a third dose, while 76 % had received a third (booster) dose (median 40 days before infection). Among those with two doses only, the excess risk for new symptoms after infection (vs. no infection) were up to 15 % for women and 9 % for men. Among infected subjects with recent booster dose, the corresponding excess risks were 7 % among women and up to 5 % among men. The largest risk differences after recent booster vaccination were seen for poor memory, brain fog, and fatigue. Post-COVID symptoms were more often detected among young and middle-aged adults than among adolescents and older age groups. Conclusion: Recent booster vaccination before infection substantially reduced both neurocognitive and cardiorespiratory symptoms occurring at least 3 months after Omicron infection.