Patients vaccinated against COVID-19 were less likely to develop long COVID following infection, regardless of changes in the virus over time, according to a study published July 17 in The New England Journal of Medicine.
Using health records from the Department of Veterans Affairs, researchers studied a group of 441,583 veterans who were diagnosed with COVID-19 between March 2020 and January 2022 and compared their outcomes with 4,748,504 non-infected individuals.
During the pre-delta, delta, and omicron eras of the pandemic, they also looked at changes between vaccinated and non-vaccinated individuals one year after initial infection.
Vaccinated individuals had a lower rate of long COVID-19 than unvaccinated.
- Pre-delta:
- Unvaccinated: 10.42 cases per 100 people.
- Vaccinated: (The study did not provide specific results for this group. But much of the pre-delta COVID era spanned a timeframe when there were not yet vaccinations.)
- Delta:
- Unvaccinated: 9.51 cases per 100 people.
- Vaccinated: 5.34 cases per 100 people.
- Omicron:
- Unvaccinated: 7.76 cases per 100 people.
- Vaccinated: 3.50 cases per 100 people.
The results also reveal that over the course of the pandemic, changes in the virus have made it less likely to turn into long COVID, but there is still a risk of developing severe long-term symptoms, even for the vaccinated.
"This is lower than earlier phases, but it is not low," Ziyad Al-Aly, MD, chief of research and development at the VA St. Louis Health Care System and a clinical epidemiologist at Washington University in St. Louis, told The New York Times. "Multiplied by the huge number of people who continue to get infected and reinfected, 3.5% per 100 adults infected will translate into millions of additional cases of long COVID."
About 28.11% fewer cases of long COVID were attributed to changes in the virus over time, while 71.89% were attributed to vaccination.