Efficacy of first dose of covid-19 vaccine versus no vaccination on symptoms of patients with long covid: target trial emulation based on ComPaRe e-cohort

OBJECTIVE: To evaluate the effect of covid-19 vaccination on the severity of symptoms in patients with long covid. DESIGN: Target trial emulation based on ComPaRe e-cohort. DATA SOURCE: ComPaRe long covid cohort, a nationwide e-cohort (ie, a cohort where recruitment and follow-up are performed online) of patients with long covid, in France. METHODS: Adult patients (aged ≥18 years) enrolled in the ComPaRe cohort before 1 May 2021 were included in the study if they reported a confirmed or suspected SARS-CoV-2 infection, symptoms persistent for >3 weeks after onset, and at least one symptom attributable to long covid at baseline. Patients who received a first covid-19 vaccine injection were matched with an unvaccinated control group in a 1:1 ratio according to their propensity scores. Number of long covid symptoms, rate of complete remission of long covid, and proportion of patients reporting an unacceptable symptom state at 120 days were recorded. RESULTS: 910 patients were included in the analyses (455 in the vaccinated group and 455 in the control group). By 120 days, vaccination had reduced the number of long covid symptoms (mean 13.0 (standard deviation 9.4) in the vaccinated group v 14.8 (9.8) in the control group; mean difference −1.8, 95% confidence interval −3.0 to −0.5) and doubled the rate of patients in remission (16.6% v 7.5%, hazard ratio 1.93, 95% confidence interval 1.18 to 3.14). Vaccination reduced the effect of long covid on patients' lives (mean score on the impact tool 24.3 (standard deviation 16.7) v 27.6 (16.7); mean difference −3.3, 95% confidence interval −5.7 to −1.0) and the proportion of patients with an unacceptable symptom state (38.9% v 46.4%, risk difference −7.4%, 95% confidence interval −14.5% to −0.3%). In the vaccinated group, two (0.4%) patients reported serious adverse events requiring admission to hospital. CONCLUSION: In this study, covid-19 vaccination reduced the severity of symptoms and the effect of long covid on patients' social, professional, and family lives at 120 days in those with persistent symptoms of infection.