Doctors studying Omicron propagation around the world have found new clues about the pattern of symptoms caused by the mutation COVID-19 variant, which a growing number of reports suggest could be displayed differently and faster compared to the Delta variant that you are now scrolling.
Preliminary evidence suggests that in many patients, Omicron is leading to a new trend of milder symptoms that mainly affect the upper respiratory system: the nose, mouth and throat. That may help explain why you seem to pose a lower individual risk hospitalization or severe illness than previous strains of the virus, which often invaded the lungs.
“What’s becoming clearer … is that Omicron appears to have less of an impact on the lungs than previous variants,” said Dr. Ronald Whelan, Discovery Health COVID-19 Task Force Leader.
The employer of Whelan, South Africa’s largest health insurer, published a report early last month on the Omicron wave there. Their analysis found that a sore throat was among the most common early symptoms of Omicron, as well as congestion, a dry cough and low back pain. The incubation period, the time from infection to the onset of symptoms, was just three days. That’s several days faster than previous strains of the virus.
Dr. Angelique Coetzee, president of the South African Medical Association, echoed Whelan’s observations about Omicron patients.
“The few who progressed to pneumonia only started around day 10-12 with shortness of breath, feeling feverish and a mild cough,” Coetzee said.
Most of the mild cases of Omicron over the course of the wave in South Africa had presented with headache, chest pain or back pain, a “mild itchy throat or dry cough and tiredness,” Coetzee said.
South Africa’s National Institute of Communicable Diseases warned residents late last month to be on the lookout for such upper respiratory symptoms, noting that a hallmark symptom seen in previous COVID variants is loss of taste. and smell, “seems to be unusual” with Omicron. .
Outbreak investigations outside of South Africa have shown similar trends.
An analysis of data collected from positive case reports in London, where Omicron cases increased last month, listed the top five symptoms as a runny nose, headache, fatigue, sneezing and sore throat.
Among the infected mostly vaccinated at a Christmas party in Norway, coughs and runny noses appeared in more than three-quarters of the 81 cases. Only 12% reported reduced odor and 23% reported reduced taste.
In an outbreak of Omicron among five reinfected people in a Nebraska home, a recent report published by the Centers for Disease Control and Prevention found that none had reported loss of taste or smell, compared to four during their first bout of COVID-19 in 2020. Two had a fever from their reinfection. An additional unvaccinated person, who had not previously been diagnosed with COVID-19, reported “cough, joint pain, congestion, fever and chills.”
The incubation period in both shoots also averaged around three days, shorter than the four to five days seen with the Delta variant.
Despite signs that Omicron leads to a lower individual risk of serious disease, it is so contagious that hospitals are fighting to handle the increasing number of cases. A consortium of disease forecasters warned on Tuesday that the United States is on track to overcome the worst days of hospitalizations and deaths from the Delta variant due to the large number of people who can contract the fast-spreading strain.
Scientists warn that Omicron’s rapid rise may be driven in large part by more people spreading the virus without any symptoms.
A study of healthcare workers in South Africa, which has not yet been peer-reviewed, found that the rate of people carrying the disease without symptoms had increased from 2.6% during outbreaks of the Beta and Delta variants to 16% with Omicron .
“These findings strongly suggest that Omicron has a much higher asymptomatic carrier rate than others. [variants of concern] and this high prevalence of asymptomatic infection is likely an important factor in the rapid and widespread spread of the variant globally, “the study authors wrote.
More clues from humans and hamsters
While the frequency of some symptoms may have changed with Omicron, doctors say there is no evidence of new or significantly different symptoms that have not been seen in Previous cases of COVID-19. Instead, scientists will need to find out how Omicron may have changed the odds of some symptoms compared to others.
For example, loss of smell or taste, called “anosmia” and “ageusia”, respectively, by doctors. emerged early during the pandemic as a telltale sign of COVID-19. However, estimates of how many cases actually cause the symptom have varied widely over the course of the pandemic and between different parts of the world.
In November, a study estimated that up to 1.6 million Americans faced long-term “chronic olfactory dysfunction” after infection.
Night sweats, another symptom cited by a doctor at a press conference in South Africa at the start of the country’s Omicron wave, has been touted by the tabloids as “a telltale sign that only occurs at night and could mean that it has been hit by the Omicron variant. ” “However, the symptom is not new: About nine out of 10 patients in a Wuhan, China report from February 2020 listed the symptom.
An analysis of cases in London last month “found no clear difference in the symptom profile of Delta and Omicron, with only 50% of people experiencing the three classic symptoms of fever, cough, or loss of the sense of smell or smell. taste, “said a post from the ZOE COVID study, which has followed trends in previous variants too.
More data on the subject is expected in the coming weeks.
Since June, monthly government surveys in the UK have consistently followed around 30% of people with positive infections who reported loss of taste or smell, and around 40% reported coughing or fatigue. A new round of survey data for December, when the Omicron variant began generating a record spike in cases there, is scheduled to be released later this month.
New clues could also come from ongoing studies investigating the effects of Omicron in animals and virus-challenged tissue samples in laboratories, which may control for factors such as immunity or underlying conditions that could cloud data on the effects of the variant in humans.
“The NIH-funded studies that are ongoing at this time in both mice and hamsters confirm the lower virulence in the animal model. And the studies here at the NIH Center for Vaccine Research, in the primate model do not humans, they are ongoing, “Dr. Anthony Fauci, the president’s top medical adviser, told reporters last week.
Fauci pointed out some preprints, which have not yet completed peer review, when studying the virus in mice and hamsters that they found signs that Omicron may spread poorly compared to Delta in the lungs. Similar findings from researchers in Hong Kong suggest that Omicron may spread faster than Delta in the tissue of the bronchus (the airway that leads to the lungs) but slower in the lungs.
“A seemingly subtle change in viral biology can have significant real-world effects on the nature of the disease that results from infection,” says Brian Willett of the University of Glasgow.
Willett is the author of a recent study, which has not yet been peer-reviewed, on how Omicron infects cells in the body.
Delta was “tuned” to infect cells by fusion, Willett said, a mechanism by which the virus can fuse with the cell membrane. Omicron seems to prefer endocytosis, a process by which the virus can enter the cell to infect it. Each pathway requires different molecules that appear in different amounts depending on the cell.
“If cells in the upper respiratory tract favor endocytosis infection, then this is where Omicron will preferentially grow. Conversely, Delta can spread deeper into the lungs as it can infect cells in this environment more efficiently.” Willett said. .