Researchers estimated the prevalence of long covid using survey data from the Netherlands in the early stages of the pandemic
One in 8 adults who had a covid-19 infection during the early stages of the pandemic developed long covid symptoms, according to survey data from the Netherlands.
Long covid is defined by the World Health Organization (WHO) as an illness that usually occurs within three months from the onset of covid-19, with symptoms that last for at least two months. These cannot be explained by an alternative diagnosis and can include chest pain, loss of smell and painful muscles.
The symptoms have many causes, so it is hard to determine how many people experience these long-term effects resulting from covid-19 infection.
Aranka Ballering at the University of Groningen and her colleagues surveyed more than 76,000 adults between 31 March 2020 and 2 August 2021 in Drenthe, Friesland and Groningen in the north of the Netherlands.
The researchers initially surveyed people weekly about their health. They then surveyed participants every two weeks from June 2020 and then just once a month from August 2020.
During the study period, 4251 people were diagnosed with covid-19 for the first time. The team matched each of these people to two others of the same age and sex who didn’t get infected.
By comparing the people who had covid-19 with the matched controls on the same dates, the researchers could better determine which symptoms experienced three to five months after infection were caused by long covid.
They defined long covid as a condition in which at least one symptom increased to moderate severity three to five months after a person developed covid-19. According to this definition, 1 in 8 people in the study who got covid-19 developed long covid. Loss of smell and taste, painful muscles and general tiredness were the most prevalent long covid symptoms.
The team also found that it took longer for long covid symptom severity to return to baseline levels in women compared with men. Some studies suggest that women face greater barriers to healthcare and so seek out help for symptoms later, and this may affect the severity of long covid, says Ballering.
The researchers couldn’t say whether these symptoms lasted beyond five months, nor could they say how badly they interfered with daily life.
The ancestral and alpha SARS-CoV-2 variants were most prevalent during the study period, so the findings may not extend to people infected with other variants. The study also doesn’t show what effect vaccines may have had on long covid. Just 10 per cent of the participants had been fully vaccinated by the end of the study, as most of the data was collected before vaccines were available.
About 98 per cent of those studied were white and they were all in the Netherlands, so these results may not extend to other ethnic and national groups. It is also unclear how long covid risk changes when people are infected with the virus multiple times, says Ballering.
“I think these figures are an underestimate,” says Danny Altmann at Imperial College London. “What I can say from my research is that I think we’re undercounting long covid, not overcounting it.”
He says this study highlights the gaps in our knowledge regarding long covid. “What we’re not good at yet is working out the nuances of long covid after different variants, such as delta.”
Journal reference: The Lancet, DOI: 10.1016/S0140-6736(22)01214-4
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