Fever, body aches, loss of smell: New COVID study charts evolution of symptoms - San Francisco Chronicle
A yearlong study of more than 60,000 people tested for the coronavirus in San Francisco found intriguing shifts in COVID-19 symptoms over three different surges — including fewer reports of loss of smell, once considered a trademark of the illness — probably because of changes in the virus itself as well as individuals' immunity.
More people with COVID reported symptoms of upper respiratory infection — including cough, sore throat and congestion — during the omicron surge than earlier waves, researchers found. Patients also experienced fewer instances of systemic issues such as fever and body aches. Loss of smell was reported by 20% of those who tested positive during the delta surge, but only 5% during omicron.
The same study, which has not yet been peer-reviewed, also found that most people infected during the omicron surge tested positive for at least five days, and in many cases up to 10 days, after their first positive test. This suggests they may remain infectious for several days after their symptoms have improved or gone away entirely, well after federal guidelines state they no longer need to isolate. California guidelines are more restrictive and recommend isolating as long as people test positive, for up to 10 days.
The findings demonstrate how COVID has become milder for many people over time, but also underscore the ways in which it remains a threat that's stubbornly difficult to control, especially as more blunt mitigation measures such as mask mandates are no longer in place and programs to support those who are ill fade away, health experts said.
"Milder illness does not mean no illness," said Dr. Diane Havlir, a UCSF infectious disease expert and senior author of the study. "It does not mean the illness doesn't affect people's ability to go to work and support their families. And we're still seeing hospitalizations. We are still in a pandemic, and we need to keep our response on pace with the virus."
The San Francisco study was conducted by researchers at UCSF and the Chan Zuckerberg Biohub in coordination with the San Francisco Latino Task Force. They looked at people who got tested at the Unidos en Salud testing site in the Mission District from January 2021 to January this year.
That period included three surges: the first fueled by the epsilon and alpha variants, the second by delta, and the third by omicron.
The study does not include results from the current surge, which is being driven by omicron subvariants but so far appears to be unfolding similarly to the most recent winter wave. Some early studies have found that the subvariants may be more likely to cause disruptive, flu-like symptoms than the original omicron.
Hospitalizations were far lower during the omicron surge — and, so far, the current surge — than previous waves, reflecting increased immunity because of vaccination and previous infection as well as a coronavirus variant that causes less severe illness in most people, health experts have said.
The Mission District study appears to support that. In addition to finding generally milder symptoms caused by omicron than earlier variants, the study showed — perhaps unsurprisingly — that symptoms also varied by vaccination status.
People who were vaccinated and boosted were actually more likely than those who were unvaccinated or not boosted to experience congestion and a sore throat — suggesting, some infectious disease experts said, that their body had a strong immune reaction to the initial infection in the nose and throat, which probably prevented the virus from infiltrating further.
Those who were unvaccinated or unboosted were more likely to report fevers and body aches — signs that the infection had penetrated beyond the upper respiratory tract and was triggering a systemic immune response.
"During omicron, you have this virus that's been shown to localize to the upper respiratory tract. Independent of the immune response, that in itself suggests that it's less likely to go systemic," said Nadia Roan, a UCSF immunologist and investigator at the Gladstone Institutes in San Francisco who was not involved in the Mission District study. "And then you have the other side, which is the immune response. That immunity will also help."
The study also looked at symptoms by age group. It found that during omicron, children younger than 12 generally reported only one symptom, with cough, fever, sore throat and congestion being most common. Throughout the study period, loss of smell was very uncommon in children — only one incident was reported in kids under 12.
Dr. Abraar Karan, an infectious disease expert at Stanford, said the overall results supported what he's heard — and experienced himself, as someone who had COVID during the omicron surge. But he noted that there's no guarantee that future variants will continue to cause milder disease, even among the vaccinated.
"It just goes to show that different variants will have different effects, clinically," he said. "But we can't always predict what these may be."
Several health experts said they were concerned by study results showing how long people were testing positive. The Mission District clinic used rapid antigen tests throughout the study period — people would get tested at the site, and have the results sent to them within 15 minutes.
Among those who returned for testing — in many cases for proof that they were safe to leave isolation and go back to work — 80% tested positive again at five days, and 60% were still positive after 10 days. The rapid tests don't necessarily prove that people are still infectious if they are positive, but scientists consider them a strong marker for infectiousness.
During the omicron surge, the CDC revised its guidance to allow people to leave isolation after five days, without testing, as long as their symptoms were improving. Many experts at the time argued that ending the previously recommended 10-day isolation period was premature; California stuck with the earlier guidance, allowing people to exit isolation early only if they tested negative.
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The Mission District study would seem to support California's more conservative approach, some health experts said. They added that it's unclear how infectious people are if they test positive after 10 days. But Havlir said earlier studies have found that they likely are at low risk of infecting others. She advised people make judgment calls at that point — perhaps continue wearing a high-quality mask indoors, and avoid being around high-risk individuals until they are negative.
"With this omicron surge, people were carrying high levels of virus certainly longer than five days," Havlir said. Her advice if they're still testing positive on day 10: "You might wait a little beyond 10 days to be 100% sure" it's safe.
She added that the results of the study also demonstrate the need for plentiful access to rapid testing — either at a community site like the one in the Mission, or with home tests. "The new public health approach is personal responsibility," she said. "We need to make sure people have what they need."
Erin Allday is a San Francisco Chronicle staff writer. Email: eallday@sfchronicle.com Twitter: @erinallday
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