New research from Israel has investigated how long it takes people who have developed long-COVID after a mild infection to recover from the condition.
Over the course of a year the study, published 12 January 2023 in BMJ, compared the health of people who had not yet caught COVID with those who had, and found that while the virus was associated with an extensive list of health conditions, these were more prominent during the first six months following infection, with most resolved after 12.
The researchers, led by Dr Maytal Bivas-Benita from the KI Research Institute, noted the findings suggest that although long-COVID has been feared and discussed since the beginning of the pandemic, most individuals with a mild infection do not suffer serious or chronic long-term illness.
“Our study suggests that mild COVID patients are at risk for a small number of health outcomes and most of them are resolved within a year from diagnosis,” Dr Bivas-Benita said.
“The overall burden of conditions after infection across the 12-month study period was highest for weakness (an additional 136 people per 10,000) and breathing difficulties (107 per 10,000).
“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.”
COVID infection was significantly associated with increased risk of loss of smell and taste, concentration, memory impairment, breathing difficulties, weakness, palpitations, streptococcal tonsillitis, and dizziness throughout the study period.
However, hair loss, chest pain, cough, muscle aches and pains and respiratory disorders were usually resolved during the last six months.
“For example, compared with non-infected people, mild COVID infection was associated with a 4.5-fold higher risk of smell and taste loss (an additional 20 people per 10,000) in the early period but only an almost 3-fold higher risk (11 per 10,000 people) in the late period,” Dr Bivas-Benita explained.
The team analysed electronic records from Maccabi Healthcare Services (MHS), the second largest health maintenance organisation in Israel, evaluating more than 70 long-COVID conditions among some two million patients who had a PCR test during the study period.
They compared conditions in unvaccinated people, with and without COVID, controlling for age, sex, and variants, during early (30-180 days) and late (180-360 days) time periods after infection, as well as conditions in vaccinated versus unvaccinated people with COVID.
To ensure only mild disease was assessed, they excluded patients admitted to hospital with more serious illness, and other potentially influential factors, such as alcohol intake, smoking status, socioeconomic level, and a range of pre-existing chronic conditions were accounted for.
“As disease severity, hospital admission, and death are dependent on age, we assessed the different long-COVID health outcomes in age subgroups in the mild disease setting and the highest number of health outcomes shown to be persistent six months after COVID were in the 41-60 years subgroup, with patients in the other age subgroups having fewer health outcomes reported,” the authors said.
“The risk for five outcomes in the 41-60 years subgroup remained significantly higher throughout the year after infection, but only dyspnoea remained significantly higher in the late period in the oldest subpopulation of >60 years.
“This might suggest that COVID would not be considered mild in older people if several symptoms persisted, resulting in patients being admitted to hospital and excluded from this study.”
Male and female patients showed minor differences, while children had fewer outcomes than adults during the early phase of COVID, which also mostly resolved during the last half of the year.
“Similarly, we observed no significant differences in health outcomes when comparing wild type/alpha and delta strains for three months after infection,” the authors said.
“These results suggest that the wild-type, alpha, and delta variants resulted in similar long term COVID sequelae, and additional assessment of long-term outcomes of the delta and the omicron variants may clarify whether long covid sequelae vary by different SARS-CoV-2 variants.
“The comparison of variants in this study was focused on relative terms and although the association between infection and outcomes was similar across variants in terms of relative risk, the absolute risk difference depends on baseline risk and may thus differ between variants.”
The researchers also highlighted limitations such as incomplete measurements within the medical records and the possibility that COVID patients may have used healthcare services more frequently, resulting in higher reporting and increased screening for potentially related outcomes in these patients.
“Nevertheless, 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 to date,” they concluded.
“Our findings should apply to similar western populations worldwide.”