Vaccinated people are less likely to get so-called long COVID, while those infected while unvaccinated may recover from persistent symptoms faster if they get the shot, a U.K. Health Security Agency review determined.
Fully vaccinated people who became infected with COVID-19 were roughly half as likely to have any symptoms lasting more than a month, 78% less likely to have symptoms lasting 12 to 20 weeks, and 13% less likely to have at least one symptom at 6 months, according to six of the eight studies summarized in a rapid evidence briefing document.
One preprint study of moderate quality suggested the opposite -- a more than twofold higher risk of symptoms at 4 weeks from the date of diagnosis versus unvaccinated participants -- but it wasn't clear why this study contradicted the rest, the document noted, calling for more analysis.
In studies that broke down symptoms individually, there was lower likelihood of developing olfactory dysfunction and significantly lower risk at 6 months for anosmia, fatigue, hair loss, interstitial lung disease, myalgia, and "other" pain.
These findings are likely an underestimate of the effectiveness of vaccination in preventing long COVID, since the studies included only vaccinated people who were infected, not those who had infection prevented entirely, the document pointed out.
The review also found that people who already had long COVID but then got vaccinated were more likely to have improvement in symptoms -- either immediately or in the weeks afterward -- compared with those who remained unvaccinated, although most had no change in symptoms and a small number had worsening after vaccination.
The one study that looked at timing of vaccination suggested that getting the shot sooner was much better than later in terms of likelihood of symptom improvement.
"These studies add to the potential benefits of receiving a full course of the COVID-19 vaccination," said Mary Ramsay, MBBS, head of immunization at the U.K. agency, in a statement. "Vaccination is the best way to protect yourself from serious symptoms when you get infected and may also help to reduce the longer-term impact."
An estimated 2% of the U.K. population reported COVID symptoms lasting more than 4 weeks after infection as of Dec. 6, 2021, well into the Omicron wave of the pandemic.
According to a prior review of mobile app data tracking cases in U.S., U.K., and Swedish populations, symptoms persisted in up to 13% of infected individuals at 1 to 2 months and in 2.6% for 3 months or longer. Potentially more reliable data from clinic-based assessments suggested that 33% to 98% of survivors have symptoms for at least a month after infection.
The U.K. Health Security Agency analysis included a total of 15 studies of long COVID: four from the U.S., four from the U.K., two from India, two online with participants in multiple countries, and one each from France, Indonesia, and Israel. Full vaccination was universally considered two doses of a two-dose vaccine series or one of a single-dose vaccine.
The document cautioned that all of the studies considered were observational. "As there are many differences between people who are and are not vaccinated, there is a risk in all these studies that factors other than vaccination status may have influenced the results (in any direction)," it pointed out.
Additionally, the studies varied widely in their definition of long COVID, and the rapid review precluded pooled or meta-analysis of the findings together.
U.K. Health Security Agency
Source Reference: UKHSA COVID-19 Evidence Team "The effectiveness of vaccination against long COVID: A rapid evidence briefing" U.K. Health Security Agency 2022.