The clue to this extraordinary possibility comes from tens of thousands of responses to US Census Bureau questionnaires that show a decreasing percentage of COVID survivors reporting long COVID symptoms – the lingering and often debilitating effects of the disease that studies have historically shown in approximately 19% of COVID Survivors.
Last June, the Census Bureau, in partnership with the National Center for Health Statistics, added questions about long COVID to its “Household Pulse Survey”, a primarily monthly online questionnaire launched in April 2020 to assess the impact of the pandemic.
The survey defines long COVID as symptoms lasting at least three months after a coronavirus infection. About 200 symptoms have been identified, with deep fatigue, heart palpitations, neurological complications and digestive disorders among the most frequent.
An average of 58,794 COVID survivors nationwide have responded to each of the nine lengthy COVID surveys offered by the Census Bureau so far. An analysis by Chronicle found a remarkable trend: a consistently lower rate of people in each survey reporting lengthy COVID symptoms.
In June, 18.9% of respondents said they were “currently experiencing” a long COVID. By the end of the year, that figure had fallen to 11.3% and by February to 10.8%.
In California, the percentage of people reporting current symptoms increased slightly in July and October, but otherwise mirrored the national trend, dropping from 16.2% in June to 10.3% in February.
“Fascinating,” said Dr. Steven Deeks, a longtime COVID researcher at UCSF unrelated to the investigations. “These trends seem consistent with the anecdotal experience we and others have had.”
Research shows that people can get long COVID whether their initial infection was severe or mild. Scientists point to three likely causes: virus fragments that remain hidden in the body, persistent inflammation caused by the coronavirus, and autoimmunity – when the body’s immune system turns against itself. These, in turn, can wreak havoc on the body months or even years later.
But is the virus’ “ability to cause long COVID waning?” Deeks asked. “That is indeed a question posed by this data.”
It is possible that the survey results reflect that some people are recovering from a long COVID. A large Israeli study published in January found that most COVID patients who had mild infections saw their persistent symptoms resolve within a year of falling ill.
Deeks and two other long COVID experts, at Stanford University and UC Davis, said the apparent decline in long COVID could be due to vaccination and the evolution of coronavirus variants that cause COVID. .
Dr. Christian Sandrock, who co-founded the long COVID clinic at UC Davis, said he has seen a drop in long COVID referrals to his clinic.
One reason, he said, could be omicron and its offshoots. “Just as omicron has more cold symptoms and fewer serious illnesses and hospitalizations” than previous variants, it also appears to produce fewer long-term symptoms, he said.
A new study by Swiss researchers to be presented at the European Congress of Clinical Microbiology and Infectious Diseases in April found that people infected with the omicron variant were less likely to report long COVID symptoms than those infected with the delta strain. of origin. These findings support findings from previous studies that suggest omicron is less likely to cause long COVID than previous variants.
Sandrock also credited the COVID vaccine.
A recent review of research in the British Medical Journal, for example, found that vaccination against COVID reduces the likelihood, severity and duration of long COVID.
Dr. Linda Geng, co-director of the long-running COVID clinic at Stanford Medicine, agreed that vaccines and new variants could be responsible for the census survey results.
However, she said, self-reported data like that from census surveys has limitations because people may define long COVID differently.
Geng said she is still seeing a lot of new patients at her long-running COVID clinic.
“Even if the rate is lower, the full scale of the problem may still be significant if large numbers of infections continue,” she said. “The only guarantee against long COVID is not to catch COVID.”
According to federal data, coronavirus cases in the United States have fallen by 40% in the past month. But there are still around 170,000 people who contract the disease every week.
And among those still suffering from long COVIDs, there is enormous frustration with the lack of viable treatments.
Some evidence has emerged that Paxlovid, an oral antiviral drug used to treat COVID-19, may help reduce the risk of ending up with long COVID.
A November study of 56,000 people with COVID found that the more than 9,000 who took Paxlovid within the first five days of their infection had a 25% lower risk of long-lasting COVID symptoms. But the data from one study is inconclusive.
In a webinar last month, White House COVID-19 response director Dr. Ashish Jha told Bob Wachter, chair of medicine at UCSF, that data showing that therapies like Paxlovid can reduce the risk of COVID long are “highly observational”.
“I wouldn’t bet on that,” he said, though he noted that “clinically it makes sense.”
Stanford researchers are hoping for clearer evidence. They are looking for candidates for a clinical trial to see if Paxlovid can treat long COVID once people already have it.
Contact Aidin Vaziri: avaziri@sfchronicle.com; Nanette Asimov: nasimov@sfchronicle.com, Twitter: @NanetteAsimov