COVID vaccination before infection strongly linked to reduced risk of developing long covid

Receiving at least one dose of a covid-19 vaccine before the first infection is strongly associated with a reduced risk of developing post-covid-19 condition, commonly known as long covid, finds a study published by The BMJ on 22nd November.

The findings, based on data for more than half a million Swedish adults, show that unvaccinated individuals were almost four times as likely to be diagnosed with long covid than those who were vaccinated before first infection.

The researchers stress that causality cannot be directly inferred from this observational evidence, but say their results “highlight the importance of primary vaccination against covid-19 to reduce the burden of post-covid-19 condition in the population.”

The effectiveness of covid-19 vaccines against SARS-CoV-2 infection and severe complications of acute covid-19 are already known, but their effectiveness against long covid is less clear because most previous studies have relied on self-reported symptoms.

Of 299,692 vaccinated individuals with covid-19, 1,201 (0.4%) were diagnosed with post-covid-19 condition during follow-up, compared with 4,118 (1.4%) of 290,030 unvaccinated individuals.

Those who received one or more covid-19 vaccines before the first infection were 58% less likely to receive a diagnosis of post-covid-19 condition than unvaccinated individuals.

And vaccine effectiveness increased with each successive dose before infection (a dose-response effect). For example, the first dose reduced the risk of post-covid-19 condition by 21%, two doses by 59%, and three or more doses by 73%.

These findings, combined with evidence from other studies, highlight the association between the immune system and the development of post-viral conditions, and underline the importance of timely vaccination during pandemics, say researchers in a linked editorial.

Reference: COVID vaccination before infection strongly linked to reduced risk of developing long covid; BMJ; DOI: 10.1136/bmj-2023-076990