Background: Long-term effects of Covid-19 are an increasing health-burden in the aftermath of the Covid-19 pandemic. Data are still scarce regarding the potential effectiveness of Covid-19 vaccines against Post Covid-19 condition (PCC).
Objectives: To investigate the effectiveness of Covid-19 vaccines against PCC among individuals vaccinated prior to Covid-19.
Methods: In Sweden, the ICD-10 code for PCC (U09.9) was implemented early during the pandemic (October 2020) and the majority of PCC cases since then have been diagnosed within primary healthcare. In this register-based cohort study, we used primary and specialist healthcare register data from the two largest regions in Sweden (Region Stockholm and Region Västra Götaland) to investigate vaccine effectiveness against PCC. Inclusion criteria were to have a first captured Covid-19 infection between 27 Dec 2020 and 9 Feb 2022 and be ≥ 18 years at study start (n= 589,722). Covid-19 infection was defined as a positive PCR test for SARS-CoV-2 or a clinical Covid-19 diagnosis (U07.1, U07.2) in primary or specialist/hospital care. Exposure was defined as having received at least one dose of a Covid-19 vaccine prior to the infection, with any of the available vaccines in Sweden. The study outcome was a diagnosis of PCC (U09.9) in any of the registers at least 28 days from the infection and until end of study (30 November 2022). Each individual was followed from Covid-19 infection until death, emigration, vaccination, reinfection, PCC diagnosis, or end of study, whichever came first. We calculated the vaccine effectiveness against PCC for any dose and stratified for one/two/three or more doses, from adjusted hazard ratios (aHR) with 95% confidence intervals (95%CI), estimated using Cox regressions adjusted for age, sex, comorbidity (diabetes and cardiovascular, respiratory, and psychiatric disease), socioeconomic factors, and period of dominant virus variant at time of infection.
Results: Of the 299,692 individuals who had received at least one vaccine dose prior to Covid-19 infection, 1201 (0.4%) received a PCC diagnosis during follow-up, compared to 4118 (1.4%) among the 290,030 unvaccinated individuals. Being vaccinated prior to Covid-19 was associated with a reduced risk to be diagnosed with PCC (aHR 0.43, 95%CI 0.39-0.47), resulting in a vaccine effectiveness of 57% against PCC. Of the vaccinated individuals, 21,111 had one dose only, 205,650 two doses, and 72,931 three doses or more. The vaccine effectiveness against PCC for one, two, and three doses were 20%, 59% and 72%, respectively.
Conclusions: In this register-based study we demonstrate a protective effect of Covid-19 vaccines against PCC. This highlights the importance of sufficient vaccination against Covid-19 to reduce the future burden of PCC in the population.
