The rapid outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) resulted in the coronavirus disease 2019 (COVID-19) pandemic. Typically, COVID-19 causes mild infection; however, some individuals experience post-acute sequelae, or long COVID, that persist for a prolonged period. 

Several post-COVID conditions (PCC) have been identified, including fatigue, respiratory symptoms, body aches, and neurocognitive dysfunction. PCC adversely affects daily activities for at least one month following SARS-CoV-2 infection.

Study: Point Prevalence Estimates of Activity-Limiting Long-term Symptoms Among United States Adults ≥1 Month After Reported Severe Acute Respiratory Syndrome Coronavirus 2 Infection, 1 November 2021, Image Credit: Maridav / Shutterstock.com

Background

A better understanding of the prevalence of PCC could help formulate evidence-based prevention and management strategies, as well as the optimal allocation of resources to combat this condition.

At present, scientists face several challenges in defining PCC and determining its prevalence. This is primarily due to the presence of non-specific symptoms and the gap in knowledge regarding the duration and pathophysiology of PCC. Furthermore, there is a lack of long-term follow-up reports on PCC.

A recent Journal of Infectious Diseases study addressed the aforementioned research gap and developed a model-based approach to estimate the point prevalence of PCC among U.S. adults on November 1, 2021.

About the study

The current study estimated the number of adult U.S. residents experiencing PCC on November 1, 2021. While developing the model, scientists selected the previously reported activity-limiting PCC symptoms related to SARS-CoV-2 infection.

PCC point prevalence estimates were developed using two primary data sources. First, the total number of adults who were at risk of developing PCC on November 1, 2021, was estimated using infection reports from the U.S. Centers for Disease Control and Prevention (CDC). The authors also used data between February 1, 2020, and September 30, 2021, from the Nationally Notifiable Disease Surveillance System (NNDSS).

To estimate the point prevalence of PCC, November 1, 2021, was selected to allow for at least a one-month interval between the time of infection and PCC manifestation. In addition, the effects of the SARS-CoV-2 Omicron variant and its sublineages were also assessed.

The household Coronavirus Infection Survey (CIS) conducted by the Office for National Statistics in the United Kingdom was the second data source. CIS provided data on non-hospitalized adults with mild or asymptomatic acute SARS-CoV-2 infection.

Study findings

In the U.S., approximately 36.3 million SARS-CoV-2 infections were reported by September 30, 2021, which included 53% females and 47% males. About 64% of adults were between 18 and 49 years old, 66% of whom were symptomatic but did not require hospitalization. Moreover, about 28% of the infected population was asymptomatic, and 6% required hospitalization for acute infection.

COVID-19 cases peaked between December 2020 and January 2021, with a record of 10 million SARS-CoV-2 infections. During this period, the Delta variant was the dominant circulating strain in the U.S.

For 22%, 44%, and 34% of infected individuals, the time between infection and November 1, 2021, was between one and six months, seven to 12 months, and more than 12 months, respectively.

The model-based approach estimated that on November 1, 2021, three to five million U.S. adults were experiencing activity-limiting symptoms of PCC. Considering the underreporting and underdiagnosis of COVID-19, 4.3-9.7 million adults were estimated to be living with activity-limiting PCC at this time. 

Previous studies have reported the dynamic prevalence of PCC, which is dependent on temporal changes associated with circulating SARS-CoV-2 variants. Therefore, a greater population-level immunity will occur with higher vaccination coverage and continual infection by the SARS-CoV-2 variants.

The current study revealed that some activity-limiting PCC symptoms persist for weeks to months after SARS-CoV-2 infection. Therefore, there is an urgent need for more epidemiological and clinical research to determine the risk factors for PCC. 

Strengths and limitations

One of the key strengths of this study is the utilization of national surveillance data on COVID-19, along with longitudinal household survey reports of individuals with mild symptoms or those who remained asymptomatic after SARS-CoV-2 infection. This is a new dimension, as most existing studies have focused on the development of PCC after severe or acute infection.

The estimates of the current study are subjected to certain limitations. For example, differential PCC risk was not considered for those who experienced reinfection due to limitations in survey data.

During the study period, most COVID-19-positive CIS participants were unvaccinated. As a result, the authors failed to determine activity-limiting PCC based on vaccination status across sex, age, and severity of the infection.

The newly developed model did not account for differences between populations in accordance with socio-demographic characteristics, underlying health conditions, and vaccine coverage and products, all of which can influence PCC development.

Despite the limitations, the current study indicated that millions of U.S. adults were experiencing activity-limiting symptoms of PCC on November 1, 2021. This model could be used as a foundation for future research to determine PCC prevalence.