Factors Associated with the Deterioration of Post-COVID-19 Condition Symptoms Following a Dose of SARS-CoV-2 Vaccine

Abstract Objectives To investigate the factors associated with the deterioration of post-COVID-19 condition (PCC) symptoms in patients who received a dose of SARS-CoV-2 vaccine ≥ 90 days after their infection. Method Multicenter cohort study conducted in 33 emergency departments across Canada, including 476 patients who developed PCC according to the World Health Organization definition. Data were collected via telephone questionnaires. Statistical analyses, including logistic regression models, were performed to identify factors associated with symptom deterioration after vaccination. Results Among participants, 28.8% reported a deterioration of their PCC symptoms after vaccination. Two factors were significantly associated with this deterioration: receiving the Moderna (mRNA-1273) vaccine (aOR = 1.80; 95% CI: 1.14–2.8) and a persistent cough three months after the initial infection (aOR = 1.81; 95% CI: 1.03–3.15). No association was found between symptom deterioration and sociodemographic characteristics such as age or sex. Conclusion Post-infection vaccination may be associated with increased risk of PCC symptoms deterioration in some patients, particularly those vaccinated with Moderna (mRNA-1273) or presenting with a persistent cough. While the benefits of vaccination remain substantial, these findings call for further investigation into the underlying immunological mechanisms and possible adjustments to vaccination strategies for patients with PCC.