Two Doses of Vaccine Linked to Lower Odds of Long COVID

Peter Russell

January 26, 2022

An analysis by the ONS found a significant reduction in the odds of developing long COVID in double-vaccinated adults but was unable to assess the impact of a third vaccine, or the effect of the Omicron variant.

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Two doses of a COVID-19 vaccine were associated with a 41.4% decrease in the odds of developing long COVID in adults aged 18 to 69, compared with unvaccinated people of the same age and from similar backgrounds, according to new figures.

However, the Office for National Statistics (ONS) said the observational nature of its analysis meant it could not say whether COVID vaccination was the determining factor in the decreased odds of self-reported symptoms.

Also, it was too early to assess the effect of 'booster' vaccines, or the impact of the Omicron variant of SARS-CoV-2.

Long COVID 'Immune Mediated' Condition

However, Dr David Strain, clinical senior lecturer at the University of Exeter Medical School, said the findings were "in keeping with the growing understanding that long COVID is, at least in part, immune mediated".

He said that findings from a study in the journal Nature Communications  this week suggested that low levels of one of the immunoglobulins was associated with the risk of long COVID.

"These are stimulated by vaccination; therefore, the evidence that vaccines are reducing the risk of progressing from COVID to long COVID is to be expected," he told the Science Media Centre (SMC).

Self-Reported Symptoms

The ONS analysis involved 6180 people in the Coronavirus (COVID-19) Infection Survey who said they had tested positive for COVID-19 for the first time between April 26, 2020, and November 30, 2021.

Participants were asked whether they would describe themselves as having long COVID, with symptoms experienced more than 4 weeks following infection. They were also asked whether their symptoms limited their ability to undertake daily activities.

Long COVID symptoms of any severity were reported by 9.5% of those who had been double-vaccinated, compared with 14.6% of individuals from similar backgrounds who were unvaccinated when infected.

Long COVID symptoms that were severe enough to limit day-to-day activities were reported by 5.5% of those who had received two vaccines, and 8.7% of people who were unvaccinated.

According to the ONS, there was no statistical evidence to suggest that self-reported long COVID symptoms differed by whether participants had received either the adenovirus vector AstraZeneca/Oxford vaccine, or the mRNA Pfizer/BioNTech or Moderna vaccines.

More Expert Reaction

James Doidge, senior statistician at the Intensive Care National Audit & Research Centre, said one "crucial" factor that the analysis could not control for was the SARS-CoV-2 variant involved, as "most of the unvaccinated group were infected during the wild or Alpha-dominant periods, whereas most of the vaccinated group were infected during the Delta wave".

He commented to the SMC: "We already know from other research that Delta is associated with about a 31% lower odds of having symptoms persisting to 28 days. This analysis indicates a 41% difference at 12 weeks, so it seems likely that much of this difference is explained not by vaccination, but by differences in the variant to which each group was exposed."

Kevin McConway, emeritus professor of applied statistics at The Open University, said that "just because we can't be sure that vaccination causes a reduction in long COVID risk, that certainly hasn't ruled out the possibility that it does cause a risk reduction".

He explained: "I think these results do provide quite a big measure of indicative evidence that double vaccination might well cause a reduction in the risk of long COVID, if one is unlucky enough to become infected after being vaccinated. But we can't be sure of that, and we also can't be sure that the size of any reduction is definitely the same as found in these results."

Commenting on the statistics for whether people had received an adenovirus or mRNA vaccine, he said "it's possible that the apparent difference between the vaccine types is entirely due to chance", but might also be because "there are differences between the people who took the two vaccine types", such as younger people who "would be less likely to have had Oxford/AZ, because it was not recommended for them".

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