• Fifteen studies were identified that reported on the effectiveness of vaccination against long COVID (search up to 12 January 2022): 7 studies examined whether vaccination before infection reduced the symptoms or incidence of long COVID, 7 studies examined whether vaccination in people with long COVID reduced or cleared the symptoms of long COVID, and 1 study examined both.

• Six of the 8 studies assessing the effectiveness of vaccination before COVID-19 infection suggested that vaccinated cases (1 or 2 doses) were less likely to develop symptoms of long COVID following infection, in the short term (4 weeks after infection), medium term (12 to 20 weeks after infection) and long term (6 months after infection). As all 8 studies included only participants who had COVID-19, the effect of vaccination on reduced incidence of COVID-19 is not accounted for. This means these studies do not give a total population estimate for the effectiveness of vaccines to prevent long COVID, but rather underestimate it.

• From 2 studies that measured individual long COVID symptoms, fully vaccinated cases were less likely to have the following symptoms in the medium or long term than unvaccinated cases: fatigue, headache, weakness in arms and legs, persistent muscle pain, hair loss, dizziness, shortness of breath, anosmia, interstitial lung disease, myalgia, and other pain.

• In studies examining the effect of vaccination among people with long COVID, 3 of 4 studies comparing long COVID symptoms before and after vaccination suggested that more cases reported an improvement in symptoms after vaccination, either immediately or over several weeks. There were, however, some cases in all studies who reported a worsening in symptoms after vaccination.

• Three studies of people with long COVID who were unvaccinated when they were initially infected, compared people who were subsequently vaccinated and people who remained unvaccinated. All these studies suggested that people with long-COVID were less likely to report long COVID symptoms shortly after vaccination, and over longer periods, than people with long COVID who were not subsequently vaccinated. One study looked at the timing of vaccination after COVID-19 diagnosis, and suggested that cases who were vaccinated sooner rather than later after diagnosis were much less likely to report symptoms of long COVID than cases who remained unvaccinated.

• In 3 of the 5 studies reporting on symptom changes following vaccination of people with long COVID, there was a higher proportion of people with long COVID who reported unchanged symptoms following vaccination (up to 70%) than people whose symptoms improved or worsened.

• All studies were observational, so the results may be from differences other than vaccination, and there was large heterogeneity between studies in the definition of long COVID.