Long Covid Symptoms Often Fade for People Who Had Mild Infection, Large Study Finds

Research from a team in Israel appears to offer encouraging news: The majority of symptoms tied to long covid might fade away over time for those who initially had a mild case of covid-19. The study found that mild cases had a higher risk of more than a dozen health conditions compared to uninfected controls in the months following infection, but this increased risk largely disappeared within a year.

The study was led by scientists from the KI Research Institute in Israel, in collaboration with Maccabi Healthcare Services, one of the country’s four health maintenance organizations (HMOs). In Israel, practically all health care is provided and covered through these HMOs—a universal system that makes it relatively easy for researchers to study the population’s health through deidentified electronic medical records. Relative to many other peer countries during the pandemic, Israel has also been more vigilant in providing residents easily accessible testing for acute cases of covid-19. The sheer amount of data available to these researchers meant that they could track people’s health following a bout of covid-19 to an extent that few others have been able to.

The study included around 300,000 people who tested positive for covid-19 infection but weren’t hospitalized as a result between March 2020 and October 2021. The team tracked how often these people went on to later be diagnosed with 70 different health conditions possibly linked to long covid up to a year later, and compared them to controls matched in age and other factors who never tested positive for covid-19 during the same period of time. They intentionally focused on those with milder covid-19, since these represent the majority of covid-19 cases and, likewise, the majority of people who develop long covid.

“The specific emphasis on patients experiencing mild disease, which are the majority of the infected population, is what adds and gives this [research] its unique point of view,” study author Maytal Bivas-Benita, a researcher at KI, told Gizmodo in an email.

Bivas-Benita’s team found that mild covid-19 cases had a higher risk on average of being diagnosed with several different conditions compared to uninfected people within one to six months after infection. These conditions, 13 in total, included hair loss, chest pain, shortness of breath, and problems with memory or concentration, commonly referred to as “brain fog.” However, this increased risk declined over the next six months, with the risk of nearly all outcomes reaching or coming close to the baseline risk seen in uninfected controls. The risk of anosmia and dysgeusia (the loss or impairment of smell and taste), brain fog, shortness of breath, and general weakness did remain elevated a year later, but these conditions became less common over time, too.

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“Patients with mild covid-19 had an increased risk for a small number of health outcomes, with only a few symptoms persisting a year from SARS-CoV-2 infection and their risk decreased with time from infection,” Bivas-Benita said. The team’s findings were published Wednesday in The BMJ.

Other studies have indicated that some people do recover from long covid, at least partially. But the authors say theirs is one of the most detailed and lengthy follow-ups of patients with initially mild covid-19.

The extensive dataset also meant that Bivas-Benital’s team could make lots of different comparisons between groups of people. Children, for instance, seem to have a lower risk of any long covid symptoms than adults, while the highest risk may be in people between the ages of 41 and 60. The risk of shortness of breath was lower in vaccinated people who developed a breakthrough infection compared to unvaccinated people, though the risk of other conditions appeared to be similar. And interestingly enough, they found no difference in long covid risk from catching either the Alpha or Delta variant, compared to the original strain, though they only had a few months of data on Delta specifically.

No study comes without caveats, though. The reliance on electronic health records and official diagnostic codes means that some cases of long covid may have gone unnoticed. And it’s possible that some people stopped reporting lingering symptoms to their doctors as time went on, even if they still felt sick. On the other hand, health care in Israel is free and considered high-quality, limiting some of the reasons why sick people would avoid or stop seeking care. And Bivas-Benita notes that people who got covid-19 may actually see the doctor more compared to uninfected people, simply because they’re paying more attention to their health following infection, “resulting in higher reporting and increased screening for potential covid-related outcomes in these patients.”

Conversely, a key strength of the study is the ability to compare these cases to a large group of uninfected controls, which is important since many symptoms often associated with long covid can be caused by other things. As a result, these findings might also indicate that only a small proportion of mild covid-19 cases go on to experience any illness that’s possibly linked to the infection. At the same time, the findings do not mean that people haven’t and will continue to experience chronic, sometimes debilitating symptoms caused by covid-19.

“It seems that as long as SARS-CoV-2 will be with us, there will be a small proportion of patients that will experience lingering symptoms of this infection,” Bivas-Benita said.

The authors say that more study is needed to understand the specific risks of long covid posed by the Omicron variant, which has become the dominant variant worldwide since late 2021. Another critical and still underexplored area is the impact of reinfections on long covid risk.

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