Key details and findings from the studies

In one study, CDC researchers analyzed data from the U.S. Census Bureau's Household Pulse Survey, which measures the social and economic impact of COVID-19 nationwide, between June 2022 and June 2023.

In the survey, respondents were asked if they ever tested positive for COVID-19 or had been diagnosed with the disease by a doctor. They were also asked if they had long COVID, which CDC described as a "wide range of ongoing respiratory, neurologic, cardiovascular, and other symptoms that can last for weeks, months, or years" after an infection.

Overall, researchers found that the prevalence of long COVID among U.S. adults decreased from 7.5% in June 2022 to 6% in June 2023. Among respondents who reported prior COVID-19 infections, the prevalence of long COVID decreased from 18.9% to 11% between June 2022 and June 2023.

In general, long COVID was less prevalent in "the youngest and oldest age groups" of respondents who reported previous infections, the researchers wrote. Individuals ages 35 to 44 were most likely to report having long COVID.

However, among individuals with long COVID, 26.4% reported "significant activity limitations" due to their symptoms, making it difficult for them to carry out daily activities like going to work or grocery shopping.

Similar findings were also reported in another CDC study. In the INSPIRE study, which was designed to assess long-term symptoms and outcomes among patients who had a COVID-like illness, researchers surveyed 1,741 people quarterly for 12 months. In total, 1,288 participants had tested positive for COVID-19, and 453 had tested negative.

Overall, the researchers found that prevalence of any long COVID symptom, including fatigue, cognitive difficulties, and more, decreased over time, with most significant decreases observed from baseline to three months. Among COVID-positive participants, symptom prevalence decreased from 98.4% to 48.2% over three months. COVID-negative participants saw their symptom prevalence decrease from 88.2% to 36.6% over the same time.

At the end of 12 months, symptom prevalence was largely similar between the two groups at 18.3% for COVID-positive individuals and 16.1% for COVID-negative individuals. However, the researchers noted that not all participants had ongoing symptoms during the study period, with some reporting new or re-emerging symptoms at different time points.

"It was common for symptoms to resolve then re-emerge months later," said Juan Carlos Montoy, the study's lead author from the University of California, San Francisco. "A lot of prior research has focused on symptoms at one or two points in time, but we were able to describe symptom trajectory with greater clarity and nuance. It suggests that measurements at a single point in time could underestimate or mischaracterizes the true burden of disease."

Commentary

Although the prevalence of long COVID has declined over time, health experts say the condition could have significant economic and social impacts, especially if patients with long COVID are unable to work.

"Limited ability to carry out day-to-day activities because of long COVID symptoms can have a significant impact on quality of life, functional status, and ability to work or provide care to others," wrote Nicole Ford, from CDC's National Center for Immunization and Respiratory Diseases, and colleagues. "Long COVID in U.S. adults has also been associated with lower likelihood of working full time and higher likelihood of being unemployed."

According to CNN, up to 23 million American may have developed long COVID. To address this issue, HHS last month announced a new Office of Long COVID Research and Practice to lead the federal government's response on the condition, and NIH launched its first clinical trials for long COVID treatments.

"As our nation continues to make strides in combating COVID-19, it is crucial that we address the impact of Long COVID and provide resources to those in need," said HHS Secretary Xavier Becerra. "Last year President Biden called on HHS to coordinate the response to Long COVID. The Official establishment of the Long COVID Coordinating office and the launch of the RECOVER clinical trials solidifies this issue as an ongoing priority." (George, MedPage Today, 8/10; Fernandez, UCSF News, 8/10; Musa, CNN, 8/10; Ford et al., Morbidity and Mortality Weekly Report, 8/11; Montoy et al., Morbidity and Mortality Weekly Report, 8/11)

As part of NIH's RECOVER trial on long COVID, researchers have developed a working case definition of the disease, outlining 12 "hallmark" symptoms to help scientists and clinicians identify long COVID more easily and investigate potential treatments.