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[3 minute read]

A new study, published today in The BMJ, suggests that COVID-19 vaccines may significantly reduce the impact of pre-existing long COVID symptoms.

The height of the COVID-19 pandemic may have passed, but across the world thousands of people are still experiencing ongoing ‘long COVID’ symptoms. These can include problems with memory and concentration ("brain fog"), fatigue, shortness of breath, and difficulty sleeping, and are often characterised by brief periods of wellness followed by relapse. In October 2021, an estimated 1.2 million people in UK private households (1.9%) were experiencing long COVID symptoms, with this having a detrimental impact on the day-to-day activities of two-thirds of these.

This has led to much interest in whether COVID-19 vaccines can reduce the incidence and severity of long COVID symptoms. Preliminary research suggests that vaccination reduces the likelihood of long COVID symptoms in subsequent breakthrough infections, however the impact of vaccination on pre-existing long COVID symptoms has been unclear. Published studies investigating this have typically been small-scale and/or with self-selecting groups of participants, meaning they may not reflect the actual situation for entire populations.

To generate more representative evidence, Dr Koen Pouwels from the Health Economics Research Centre at Oxford Population Health helped coordinate a study which used data from the Office for National Statistics COVID-19 Infection Survey (CIS). This survey, the biggest COVID-19 household survey in the world, collects nose/throat swabs and blood tests from a large representative sample of UK residents each week to test for coronavirus antibodies (regardless of whether the individuals are experiencing COVID-19 symptoms or not). Dr Pouwels co-designed the survey, and has been its methodological lead throughout.

For this investigation, the research team analysed data from over 28,000 CIS participants (aged 18 to 69 years) who had all received at least one COVID-19 vaccination dose after a test-confirmed SARS-CoV-2 infection. From February 2021, all CIS participants were visited each month by a survey team member and asked if they were experiencing any long COVID symptoms. The researchers analysed data from the monthly visits that took place between 3 February 2021 and 5 September 2021.

Key findings

  • Over the study period, participants had a median of four visits after their first vaccination dose and, among those double-vaccinated (84% by September 2021), a median of two visits after their second dose. Around 6,700 participants (24%) reported long COVID symptoms at least once during the follow-up period.
  • The odds of experiencing long COVID symptoms that had persisted for at least 12 weeks initially fell by an average of 13% after receiving a first COVID-19 vaccination. Before vaccination, there was little change in the odds of experiencing long COVID over time (-0.3% per week).
  • Receiving a second vaccination was associated with a further 9% decrease in the odds of long COVID symptoms, and followed by a sustained decrease of around 0.8% per week up to the end of the study period.
  • There was no statistical evidence that the type of vaccine affected the impact on long COVID symptoms.
  • There was no statistical evidence that the impact of vaccination on long COVID symptoms varied according to socio-demographic characteristics (age, sex, ethnic group, deprivation) or health-related factors (general self-reported health status, and whether they had previously been hospitalised with severe COVID-19).

According to the researchers, although causality cannot be inferred from this observational evidence, the results support proposed biological mechanisms for how vaccination may reduce long COVID symptoms. For instance, any remaining viral reservoirs may become destroyed by the antibody response, whilst long COVID symptoms caused by immune system dysregulation may benefit from vaccine-induced diversion of autoimmune processes. However, whether vaccination induces a long-lasting ‘reset’ of the immune system remains to be established.

Dr Pouwels said: ‘This is the largest study to date internationally on long COVID and COVID-19 vaccination, and the first to investigate post-vaccine symptom trajectories. Our results suggest that vaccination of people previously infected may be associated with a reduction in the burden of long COVID, at least in the first few months following vaccination. Further research is needed to evaluate the long-term relationship between vaccination and long COVID, including the impact of the Omicron variant, and the roll-out of booster doses.’