Although most cases of SARS-CoV-2 infection resolve within two to four weeks of the appearance of symptoms, some patients experience long COVID, defined as persistent or new symptoms that cannot be attributed to another condition and last for four weeks or more after the diagnosis of primary COVID-19. In a retrospective cohort study, researchers evaluated health outcomes in people with mild SARS-CoV-2 infection and people who weren't infected, controlling for age and sex and with stratification by variants, and in vaccinated versus unvaccinated people who had a SARS-CoV-2 infection.

They reviewed the health records of all members of an Israeli nationwide health care organization who had a SARS-CoV-2 polymerase chain reaction (PCR) test between March 2020 and October 2021. The 299,885 eligible members with complete data who tested positive and weren't admitted to the hospital were matched with 299,870 people who tested negative.

Compared with uninfected controls, unvaccinated patients who had a mild SARS-CoV-2 infection were at significantly increased risk for anosmia (loss of smell) and dysgeusia (loss of taste), concentration and memory impairment, dyspnea, weakness, palpitations, streptococcal tonsillitis, and dizziness during two time periods after a positive PCR test, the early (30 to 180 days) and late (180 to 360 days) phases. Respiratory disorders, hair loss, chest pain, myalgia, and cough were significantly increased only during the early phase.

Patients of all ages who tested positive for SARS-CoV-2 were at significantly increased risk for multiple health outcomes. Most health outcomes were similar in men and women, and findings were consistent across SARS-CoV-2 variants. Vaccinated patients who had breakthrough infections were at lower risk for prolonged dyspnea than unvaccinated controls but at similar risk for other health outcomes.

The authors point out that the incidence of minor diagnoses may be underestimated, and patient-reported outcomes, such as weakness and cognitive impairment, might not be uniform and accurate. Among other study limitations were that infected patients may be more likely to report and be screened for possible COVID-related outcomes, symptoms in the later periods may be underreported, and only people who had PCR tests were included in the study.