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Since long Covid emerged, how best to define it, predict it, and treat it has been up for debate, but perhaps the most urgent question for patients and providers alike has been how long it lasts. A new study analyzing nearly 2 million patient records in Israel concludes that for most people, the troubling symptoms that persist after a mild Covid infection fade away after about a year.

Just as estimates of long Covid’s prevalence have varied widely, so have conclusions about a variety of symptoms. Covid infections reach into multiple organ systems, as does long Covid. Scientists have reported on some neuropsychiatric conditions lingering for two years, for example, but the team from the KI Research Institute wanted to paint a broader picture of long Covid’s duration.

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“When we started this study there was a lot of uncertainty regarding the long-term effects of the pandemic and there was a fear that a large proportion of infected individuals will have long-lasting symptoms and emergence of new morbidities,” the study’s senior author Maytal Bivas-Benita and lead author Barak Mizrahi said in a joint email to STAT. “As we analyzed the data, we were surprised to find only a small number of symptoms that were related to Covid and remained for a year post infection and the low number of people affected by them.”

For their paper published Wednesday in BMJ, the researchers analyzed 1,913,234 patient records from Maccabi Healthcare Services, a large health maintenance organization in Israel whose members were tested for Covid-19 from March 2020 to October 2021, when the original virus and the Alpha and Delta variants were circulating. After compiling a list of 70 long Covid symptoms, they looked for them at different time points, comparing the nearly 300,000 patients who tested positive to comparable patients who tested negative for Covid-19, excluding anyone hospitalized for the illness.

Studying non-hospitalized patients better reflects the vast majority of people who contract Covid, they said, also making it easier to tease out effects caused by the virus and not by intensive care treatments such as ventilators. “We wanted to truly understand what are the long-term effects of this infection on the majority of the population and whether we should expect a significant burden on healthcare providers,” Bivas-Benita and Mizrahi wrote.

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Throughout the year of follow-up, patients with mild Covid-19 had an increased risk of problems including loss of smell and taste, concentration and memory impairment, breathing difficulties, weakness, palpitations, strep throat, and dizziness. Later in the year, health records showed more hair loss (particularly among women), chest pain, cough, muscle aches and pains, and respiratory disorders among Covid patients. But for most people, these problems also cleared up by the end of one year.

Vaccinated people were at lower risk of developing breathing difficulties after breakthrough infections — the most common problem after mild infection, along with weakness — compared with unvaccinated people, but their risk was similar for other conditions. People from 41 to 60 years old had more health problems than people in other age groups, and shortness of breath continued to be a problem for those over 60.

Children had fewer long Covid symptoms than adults, and most of those issues were gone after a year. “This is a reassuring large population medical record study,” Michael Absoud, honorary reader in the Department of Women & Children’s Health at King’s College London and not involved in the study, said. “It confirms that in children, of the small proportion who have prolonged persistent symptoms post SARS-CoV-2 infection, the vast majority show a very good recovery.”

There were minor differences between men’s and women’s risk of outcomes, and findings remained consistent across the SARS-CoV-2 variants that emerged before Omicron.

“The general message that symptoms improve over time is encouraging, but it may take a year or so for some symptoms to resolve,” Peter Openshaw, a professor of experimental medicine at Imperial College London, said. He was not involved in the research. “The study adds to the evidence that outcomes are improved by vaccination, even if vaccines don’t prevent viral transmission very well.”

Ziyad Al-Aly, clinical epidemiologist at Washington University in St. Louis, isn’t so sure. He thinks the study’s message may be too optimistic, owing to its design. Comparing people who test positive to people who test negative may not account for the reason people are taking Covid tests. Someone with cancer might need to test before starting chemotherapy, he said, or someone else might need surgery for another reason.

“Better designs would be needed to more confidently elevate our understanding, to actually deepen our understanding of the the toll and scale of the condition and the trajectory of the health performance of the individual affected with long Covid over the the ensuing year after that infection,” Al-Aly, who is also chief of research and development at the VA St. Louis Health Care System, told STAT. He was not part of the study. “It doesn’t mean that some people are not improving. We see a big improvement in some individuals … . I wish this was normally the case, but it’s really too rosy to be true.”

In response, the study authors said it’s important to remember that PCR tests to detect Covid-19 were offered to all Israeli citizens free of charge, without needing a referral, throughout the entire study period. That meant 76% of Maccabi Healthcare Services’ members took at least one PCR test during the study period. And they say “chances are minimal” that those test-negative patients would be more likely to have symptoms like long Covid because any chronic conditions they had at baseline were matched to test-positive patients who also had them. And, they pointed out, infectious diseases other than Covid were rare during social distancing and lockdown in effect during the study period.

The researchers acknowledged that not everyone recovers. And their results come from one country.

“We are not claiming there are no patients who suffer from long Covid symptoms (like dyspnea, weakness, cognitive impairment etc.),” they wrote in a follow-up email. “This does not contradict evidence that a small number of patients do suffer from long lasting symptoms as seen in this analysis.”

Next on their research agenda: evaluating the effects of the Omicron strain and assessing the prevalence and severity of outcomes following reinfections.

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