For most patients with long Covid after an initial mild infection, symptoms may linger for several months but will resolve within a year, a large study has concluded.
The analysis of healthcare records from 2 million people in Israel also found that vaccinated people were at lower risk of breathing difficulties – the most common ongoing symptom after mild infection.
Reporting the findings in the BMJ, the researchers also said of the small proportion of children who had persistent symptoms after Covid-19 infection, the vast majority recovered.
Latest figures from the Office for National Statistics published on the 5 January show an estimated 2.1 million people in the UK, or 3.3% of the population, were experiencing self-reported long Covid symptoms for more than four weeks.
This includes 1.9 million people (87%) who believe they had Covid at least 12 weeks previously, 1.2 million (57%) at least one year previously and 645,000 (30%) at least two years previously.
The Israeli analysis of healthcare records between March 2020 and 1 October 2021 looked at more than long Covid conditions in infected and matched uninfected individuals as well as comparing vaccination status and Covid variants.
Anyone admitted to hospital with more severe illness was excluded from the study and other chronic conditions and socioeconomic status were taken into account.
Mild Covid-19 infection was associated with a 4.5-fold higher risk of loss of smell and taste in the early period classed as 30 to 180 days after infection and an almost 3-fold higher risk in the late period, which was defined as 180-360 days.
The symptoms with the highest burden across the early and late phases were weakness and breathing difficulties, the researchers said.
Breathing difficulties remained persistent throughout the first year post-infection in the 19-40, 41-60, and over 60 years age groups.
The patterns identified in the study were similar across the wild-type, Alpha and Delta Covid-19 variants.
But the analysis also showed that vaccinated people who became infected had a lower risk of breathing difficulties compared with unvaccinated infected patients although a similar risk of other symptoms.
‘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’ they concluded.
‘Importantly, the risk for lingering dyspnoea was reduced in vaccinated patients with breakthrough infection compared with unvaccinated people,’ they added.
Professor Peter Openshaw, professor of experimental medicine, Imperial College London, said the size of the study meant the researchers could look at the change in symptom prevalence over time and the effects of other factors on persistent symptoms.
He noted that loss of smell tended to resolve at about nine months but concentration and memory changes tended to be more persistent.
‘Persistent shortness of breath tended to resolve over time and vaccination was associated with lower risk of developing it.
‘The general message that symptoms improve over time is encouraging, but it may take a year or so for some symptoms to resolve.
‘The study adds to the evidence that outcomes are improved by vaccination, even if vaccines don’t prevent viral transmission very well.’