Most long COVID symptoms that develop after a mild infection of the virus normally disappear within a year, according to a newly published study.
The research, published in The BMJ, also found that vaccinated people had a reduced risk of breathing difficulties compared with unvaccinated people.
The team from KI Research Institute, Kfar Malal, and Maccabi Healthcare Services, Tel Aviv, Israel, say their findings suggest the vast majority of people who suffer milder symptoms do not go on to have serious or chronic long term illness.
The researchers examined the clinical effects of long-COVID one year after mild infection and their association with age, sex, COVID-19 variants, and vaccination status.
They compared the health of uninfected individuals with those who had recovered from mild COVID-19 for a year after infection, using the electronic records of a large public healthcare organisation in Israel, in which almost two million members were tested for COVID-19 between 1 March 2020 and 1 October 2021.
More than 70 long-COVID conditions were analysed in a group of infected and matched uninfected members, whose average age was 25. Just over half were female.
They compared conditions in unvaccinated people, with and without COVID-19 infection, controlling for age, sex and COVID-19 variants, during early (30-180 days) and late (180-360 days) time periods after infection.
Conditions in vaccinated versus unvaccinated people with COVID-19 were also compared over the same time periods.
To ensure only mild disease was assessed, they excluded patients admitted to 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.
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.
The overall burden of conditions after infection across the 12-month study period was highest for weakness, at an additional 136 people per 10,000, and breathing difficulties at 107 per 10,000.
When conditions were assessed by age, breathing difficulties were the most common, appearing in five of the six age groups but remaining persistent throughout the first year.
Weakness appeared in four of the six age groups and remained persistent in the late phase only in the 19-40 and 41-60 age groups.
There were minor differences between male and female patients showed, 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.
The team also found vaccinated individuals who became infected had a lower risk of breathing difficulties and similar risk for other conditions compared with unvaccinated infected patients.
“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,” say the researchers.
“Importantly, the risk for lingering dyspnoea was reduced in vaccinated patients with breakthrough infection compared with unvaccinated people, while risks of all other outcomes were comparable,” they add.
Mizrahi B, Sudry T, Flaks-Manov N et al. Long COVID outcomes at one year after mild SARS-CoV-2 infection: nationwide cohort study. BMJ 12 January 2023; doi: 10.1136/ bmj-2022-072529
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