air 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