The chances of developing long-term COVID decreased as the coronavirus evolved

As new varieties of the coronavirus took center stage during the COVID-19 pandemic, the likelihood of developing long-term COVID declined. Those who were vaccinated against the virus saw the greatest decline over time.

For every 1,000 unvaccinated people, 104 developed long-term COVID up to a year after an infection during the pre-delta phase of the pandemic. This dropped to 95 per 1000 during the era of delta variants and 78 during the reign of the omicrons. Among vaccinated people, only 53 out of 1,000 developed COVID up to a year after infection during delta and only 35 during omicron, researchers report July 17 at. New England Journal of Medicine.

The US Department of Veterans Affairs Healthcare System data study looked at people who had a COVID infection from March 2020, the month the pandemic began, to the end of January 2022. The researchers, from the Veterans Affairs Healthcare System in St. , compared the rates of COVID during three phases of the pandemic between those who were vaccinated and those who were not. The first vaccine against COVID was introduced in December 2020 (SN: 12/11/20). The delta variant dominated the United States in the summer of 2021, with the omicron variant starting in December 2021 (SN: 7/2/21; SN: 21.12.21).

A comparison of omicron infections with infections from previous eras found that 72 percent of the long-term decline in the rate of COVID during the omicron was attributable to vaccines. The rest was due to changes in the virus and improvements in medical care and the use of antiviral treatments during the omicron phase.

Even with the large decline in the incidence of long-term COVID for vaccinated persons, there is still a risk, the researchers write. With the high number of new infections and reinfections ongoing, and poor vaccination uptake continuing, this could translate into a high number of people with long-term COVID.