Impact of Pre-Infection COVID-19 Vaccination on the Incidence and Severity of Long COVID: A Retrospective Case–Control Study

Long COVID is an emerging condition with an important impact on the quality of life of affected individuals. This study aims to analyse the association between complete vaccination prior to SARS-CoV-2 infection and the subsequent development of long COVID, including its symptoms and their frequency through a retrospective case–control study. Cases included participants with long COVID, while controls were participants without long COVID but who had a SARS-CoV-2 infection. Data were collected through a self-reported survey. The study demonstrates a significant association between vaccination and a lower incidence of long COVID, adjusted for sex, age, university education, body mass index, physical activity, race, tobacco use, alcohol intake, adherence to Mediterranean diet, previous illness, flu vaccination, health care worker, high-risk COVID worker and sleep hours and sedentarism (OR 0.49, CI 95% 0.28–0.87). Furthermore, there is a statistically significant association between vaccination and reduced symptoms such as anosmia, dysgeusia, myalgia or arthralgia, as well as a lower overall number, adjusted for the aforementioned variables. These findings suggest that the vaccine could be associated not only to a milder course of SARS-CoV-2 infection but also with an improvement in the state of long COVID and its symptoms.