Study: Most Long COVID-19 Symptoms Resolve Within a Year After Mild Infection

Most long-term symptoms that develop after a mild COVID-19 infection resolve within a year, according to a large study published in The BMJ.

In addition, researchers found that vaccinated individuals had a lower risk of breathing difficulties—the most common symptom to develop after mild infection—compared with unvaccinated individuals. These findings suggest that, although long COVID-19 has been feared and discussed since the beginning of the pandemic, the vast majority of mild cases do not suffer serious or chronic long-term illness.

Long COVID-19 is defined as symptoms persisting or new symptoms appearing more than 4 weeks after initial COVID-19 infection. In March 2022, an estimated 1.5 million individuals in the United Kingdom (2.4% of the population) reported long COVID-19 symptoms, which consisted mostly of fatigue, shortness of breath, loss of smell, loss of taste, and difficulty concentrating.

However, the clinical effects of long COVID-19 lasting 1 year after mild infection and the association with age, sex, COVID-19 variants, and vaccination status are unclear. To address this, investigators compared the health of uninfected individuals with those who had recovered from mild COVID-19 for a year after infection.

They used electronic records of a large public health care organization in Israel, in which nearly 2 million members were tested for COVID-19 between March 1, 2020, and October 1, 2021. More than 70 long COVID-19 conditions were analyzed in a group of infected and matched uninfected participants, with an average age of 25 years and 51% female.

Researchers compared conditions in unvaccinated participants, with and without COVID-19 infection, controlling for age, sex, and COVID-19 variants, during early (30 to 180 days) and late (180 to 360 days) time periods after infection. Conditions in vaccinated versus unvaccinated people with COVID-19 were also compared over the same time periods.

To ensure that only mild disease was assessed, the investigators excluded patients admitted to the hospital with more serious illness. Other potentially influential factors, such as alcohol intake, smoking status, socioeconomic level, and a range of pre-existing chronic conditions were also taken into account.

According to the study findings, COVID-19 infection was significantly associated with increased risks of several conditions, including loss of smell and taste, concentration and memory impairment, breathing difficulties, weakness, palpitations, streptococcal tonsillitis, and dizziness in both early and late time periods. Hair loss, chest pain, cough, muscle aches and pains, and respiratory disorders resolved in the late period.

For example, compared with non-infected individuals, the study found that mild COVID-19 infection was associated with a 4.5-fold higher risk of smell and taste loss in the early period and an almost 3-fold higher risk in the late period. The overall burden of conditions after infection across the 12-month study period was highest for weakness and breathing difficulties.

When conditions were assessed by age, breathing difficulties were the most common, appearing in 5 of the 6 age groups but remaining persistent throughout the first year post-infection in the 19 through 40, 41 through 60, and over 60 years of age groups. Weakness appeared in 4 of the 6 age groups and remained persistent in the late phase only in the 19 through 40 and 41 through 60 age groups.

The study also found minor differences between male and female patients, and children had fewer outcomes than adults during the early phase of COVID-19, which mostly resolved in the late period. Findings were similar across the wild-type, Alpha, and Delta COVID-19 variants.

Vaccinated individuals who became infected had a lower risk of breathing difficulties and similar risk for other conditions compared with unvaccinated infected patients.

The study authors noted some limitations, such as incomplete measurement within medical records, so data may not fully reflect diagnoses and outcomes reported. The researchers also cannot rule out the possibility that COVID-19 patients may use health care services more frequently, resulting in higher reporting and increased screening for potential COVID-19-related outcomes in these patients.

Despite these limitations, this was a large, detailed analysis of health records across a diverse population, representing one of the longest follow-up studies in patients with mild COVID-19 to date. The findings should apply to similar western populations worldwide.

“Our study suggests that mild COVID-19 patients are at risk for a small number of health outcomes and most of them are resolved within a year from diagnosis,” the researchers said in the study. “Importantly, the risk for lingering dyspnea was reduced in vaccinated patients with breakthrough infection compared with unvaccinated people, while risks of all other outcomes were comparable.”

REFERENCE

Most long covid effects resolve within a year after mild infection. News release. EurekAlert; January 11, 2023. Accessed January 16, 2023. https://www.eurekalert.org/news-releases/976030