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How the omicron variant differs from delta

The extremely transmissible omicron variant continues to cause record numbers of COVID-19 cases and deaths, despite causing less severe disease than delta.

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For the most up-to-date news and information about the coronavirus pandemic, visit the WHO and CDC websites.

While the average daily rate of COVID-19 cases is falling in the US, deaths are not. The country continues to feel the weight of record-breaking numbers of COVID-19 cases and hospitalizations, and has pushed the US past a new grim milestone of more than 900,000 deaths from COVID-19. At a White House COVID-19 response team briefing last week, Dr. Rochelle Walensky, director of the US Centers for Disease Control and Prevention, said that while the average number of daily COVID-19 cases decreased about 36%, deaths had increased about 4% from the previous week. Although experts predicted this gap in hospitalization and death data, it reflects the unmoving reality than many people are still dying from COVID-19.

"We're seeing these rapid declines in cases, but what I want to emphasis is that health care and public health is still very stressed in many places, and our case numbers are still higher than we saw with any previous peak," Crystal Watson, senior scholar at the Johns Hopkins Center for Health Security, said at a media briefing last week. 

Even though it's understood now that omicron generally causes less severe disease for the individual than the delta variant, omicron's extreme contagiousness compared with previous variants that dominated the globe has caused huge numbers of people to get sick, with some inevitably getting seriously ill. And comparing omicron with delta should also come with the understanding that the delta variant was more contagious than earlier variants, and also appeared more likely to put people in the hospital. That is, when comparing the omicron and delta variants, we're comparing omicron with a very serious illness. Dr. Eric Topol, a physician and professor of molecular medicine at Scripps Research, told The Guardian that "less severe" is a better way to describe omicron than "milder." 

"'Milder' caught on early, and I think it's unfortunate it's given this impression, because there are so many people dying and winding up in the ICU," Topol told The Guardian. 

Does omicron cause less severe disease than delta? 

For the individual, yes. (The record numbers of infections continue to cause many deaths and overwhelm hospital systems.) A preprint study published last month looked at data from about 52,000 people infected with the omicron variant, and about 17,000 infected with delta, in southern California. Compared with patients who had the delta variant, omicron patients had a 53% reduced risk of hospitalization, a 74% reduced risk of ICU admission and a 91% reduced risk of death. The study has not yet been peer-reviewed.

When talking about the study at a briefing last month, Walensky said that none of the people infected with omicron in the study required mechanical ventilation. This backs up another study from researchers in Hong Kong who found that while extremely contagious, omicron isn't as good at replicating in the lungs as delta, likely leading to less severe disease. 

The new research also adds to what researchers from many other countries, including South Africa, have found: Though more contagious than any other variant, omicron doesn't seem to be making people quite as sick as the delta variant did. And when it does make people sick enough to require hospitalization, those hospital stays tend to be shorter, Walensky noted. 

What is a mutation or variant? 

Some mutations in omicron's spike protein are similar to ones found in the delta variant, according to South Africa's Department of Health, as well as mutations found in the alpha, gamma and beta variants -- all classified as variants of concern by the World Health Organization.

Omicron has more mutations on its spike protein than the delta variant does, but scientists are working to understand what that means.

The coronavirus enters our cells using its "corona," or layer of protein spikes, then makes copies of itself in our bodies, where inevitably there are some errors or mutations, as explained by Yale Medicine. Sometimes those mutations in the virus are harmless, but other times -- as in the case of the delta and omicron variants -- they make it much easier for the virus to spread from person to person and infect more people. 

The more people who are unvaccinated or without immunity from COVID-19, the more opportunities there are for the coronavirus to spread and form concerning variants. 

"I think what you're seeing is just the manifestation of what we've been talking about," Fauci told NBC in November. "Why it is so important for people to get vaccinated, and for those who are fully vaccinated to get boosted."

Apart from vaccine hesitancy, many people in countries outside the US don't have access to a COVID-19 vaccine. According to Our World in Data, 9.4% of people in low-income countries have received a dose of coronavirus vaccine. 

"The emergence of the omicron variant should be a wake-up call to the world that vaccine inequality cannot be allowed to continue," South Africa's president, Cyril Ramaphosa, said in a November address

At a recent press briefing, White House COVID-19 Response Coordinator Jeff Zients said the US has shipped 300 million COVID-19 vaccine doses out for donation, a milestone, he said, in the White House pledge to donate 1.2 billion doses of COVID-19 vaccine to other countries. 

Is it omicron or a cold? 

Given the extremely high number of COVID-19 cases and community spread throughout the US, you should probably treat your sniffles or sore throat like they're COVID-19, and stay home if you're sick. But of course, the only way to know for sure is to get tested.

In fully vaccinated and boosted people, especially, omicron is causing mild cases of COVID-19 that can mimic run-of-the-mill cold symptoms. 

In a Dec. 10 report by the CDC, the symptoms of 43 omicron cases (some of the first reported in the US) were described. When it came to common symptoms, most people (89%) reported a cough, 65% were fatigued and 59% of them were congested or had a runny nose. Only 8% of the 43 people reported losing their sense of smell or taste, which has affected many people with previous COVID-19 infections, caused by other variants. Fourteen percent of people in the report had COVID-19 previously. 

Dr. Angelique Coetzee, a South African doctor who helped discover omicron, told the BBC in late November that the early symptoms she saw in patients included fatigue, headache and a scratchy throat, she said, not the telltale loss of smell or a cough associated with earlier COVID-19 infections. 

Cough and loss of smell are also less common symptoms of COVID-19 caused by the delta variant compared with earlier variants, per the Baton Rouge General, a Mayo Clinic network. Cold symptoms like a headache and runny nose are now more common symptoms of COVID-19, according to the UK's ZOE COVID Study.

How do you test for omicron? 

A COVID-19 test won't tell you which variant you have. In order for scientists to determine whether it's omicron or another coronavirus variant, the CDC uses genomic sequencing. According to Walensky, the CDC director, the US is now testing 80,000 positive COVID-19 samples per week (about one in seven positive tests), up from 8,000 per week earlier this year.

Fortunately, the omicron variant is easily detected through PCR tests, according to Fauci, which can then be confirmed through labs that use genomic sequencing. 

Read moreCan you tell which COVID variant you have?

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.