A new study of nearly 70,000 Covid patients in California shows that Omicron causes less severe disease than other variants of the coronavirus, findings that match similar findings in South Africa, Great Britain and Denmark, as well as a multitude of animal experiments.
Compared with Delta, infections with Omicron were half as likely to send people to hospital. Of more than 52,000 Omicron patients identified from electronic medical records from Kaiser Permanente of Southern California, a large healthcare system, the researchers found that no patient had used a ventilator during this time.
“It’s really a viral factor that explains the reduced severity,” said Dr. Lewnard, an epidemiologist at the University of California at Berkeley, author of the study, which was published online Tuesday and has yet to been published in a scientific journal. newspaper.
Despite Omicron’s less severe virulence, US hospitals are caving in under an influx of coronavirus cases. Dr Lewnard said it was the result of the variant spreading like wildfire. On average, more than 730,000 people test positive every day in the United States, nearly three times the previous peak last winter.
“Since it’s more communicable, there will be just at one point a lot of hospitalizations that will inevitably occur,” Dr Lewnard said.
In recent weeks, Britain and several other countries have reported that Omicron has a lower risk of hospitalization. When the variant hit the United States last month, Dr Lewnard and his colleagues began analyzing electronic health records kept by Kaiser Permanente of Southern California, which serves 4.7 million people.
They analyzed 69,279 symptomatic patients who tested positive for the coronavirus from November 30 to January 1. Three-quarters of the positive samples contained the Omicron variant, and the rest were Delta.
The researchers then followed those who tested positive to see if they ended up in the hospital. They ruled out so-called accidental Covid patients who presented to hospitals with other complaints and tested positive for the coronavirus after arrival.
Compared to Delta, Omicron halved the risk of hospitalization, the study found, and people who came to the hospital with Omicron stayed shorter. The variant reduced hospital stays of more than three days, a 70% reduction compared to Delta.
Fourteen of the patients infected with Delta have died, while only one patient from Omicron has died.
While scientists have gathered evidence that Omicron is less severe, they have struggled to understand why. One of the reasons is that people infected with Omicron have more immune defenses than in previous waves.
In other countries, researchers have found that earlier infections with other variants lowered the chances that people would get seriously ill with Omicron. Vaccination also offers protection.
“Vaccines are very helpful,” said Dr Lewnard. He and his colleagues found that vaccinated Californians were 64 to 73 percent less likely to be hospitalized than unvaccinated people.
However, even among unvaccinated people, Omicron was less likely to lead to hospitalizations than Delta.
Dr Lewnard said this additional analysis showed Omicron to be fundamentally less severe. Animal studies suggest that Omicron easily infects cells in the upper respiratory tract but functions poorly in the lungs, which could explain its milder effects.