Omicron: The Most Contagious Virus in History

The new SARS-CoV-2 variant is spreading like wildfire and causing record-breaking numbers of COVID-19 cases. EXPLAINER

First detected in November 2021, within just three months, the Omicron variant has invaded almost every country in the world. This variant differs from the others: It is usually milder, causing cold-like symptoms with a runny nose, sneezing and a sore throat, rather than the coughing, fever and loss of taste and smell of the earlier variants. But Omicron is far more contagious, And it can still kill.

How Omicron works

Omicron spreads quickly. The earliest coronavirus variants had an average incubation period of roughly five days. The Delta variant moved faster at four days, and for Omicron, it’s about three. For a virus, this is lightning speed even compared to the highly contagious measles virus, where one person can infect 15 other people in 12 days. Omicron doubles every 2-3 days, with one case spreading to six people in four days, 36 people in eight days, and a hefty 216 people after 12 days.

Omicron already has about 50 mutations. The BA.1 and BA.2 Omicron variants have 13 mutations on their spike protein rarely seen in other variants that boost the virus’ ability to enter the body and alter our immune system’s response to it. Additionally, BA.2 has about 28 different mutations than BA.1, though they seem to behave similarly. However, BA.2 lacks a mutation that makes it harder to detect with PCR tests. NOT CLEAR: WOULD THAT MUTATION MAKE IT EASIER TO DETECT, OR THE OPPOSITE?

ACE2 receptor and Omicron

To enter our bodies, the SARS-CoV-2 spike protein binds to a protein receptor on our cells called Angiotensin-Converting Enzyme 2 (ACE2). The antibodies created by COVID-19 vaccines and natural infections block this binding and inhibit the virus from entering our cells. However Omicron has mutations of the spike protein that allow it to hide from our immune system. In fact, there are at least 15 mutations our antibodies don’t recognize, which means they can no longer block the virus from entering our cells. That’s why we see breakthrough cases.

And to make matters worse, Omicron has mutations that stabilize the spike protein and enhance its ability to bind to ACE2. So while vaccines remain effective – they still ward off serious illness, especially after having booster shots – the protection is less complete.

TMPRSS2 and Omicron

The previous SARS-CoV-2 virus variants use a special protein – the trans-membrane serine protease 2 (TMPRSS2) – to facilitate getting into the cells. But Omicron has found another way: Our cells actually engulf Omicron and allow it to enter.  

Biologically, this is a significant advantage because the TMPRSS2 protein is not on all cells. Because Omicron doesn’t need it, it can infect any cell.  The Delta variant, in contrast, targets TMPRSS2 expressing cells – lung cells among them, which is why the lungs are particularly vulnerable to coronavirus infection and damage.

So Omicron can infect all cells, and because it replicates so quickly, it tends to infect the first cells it finds, usually in the nose and trachea, and doesn’t reach the lungs. The lack of lung cell involvement explains why Omicron causes fewer hospitalizations, the need for intensive care and mechanical ventilation. On the downside, with higher numbers of the Omicron variant invading and replicating in the nose, there’s more spread when infected people cough and sneeze.

In addition, the Omicron variant, unlike the earlier COVID variants, is more vulnerable to “interferons”, the small proteins, plentiful in the lungs, that are part of our general viral immune response.

Less able to get around the interferons, Omicron takes hold instead in the nose and upper airways, yet causes milder disease.  

Tips for Omicron

Remember, Omicron’s mutations cause mild disease in many but still can cause severe illness in unvaccinated or immunosuppressed people and even others without risk factors. So, it’s best to avoid getting it in the first place.

Here are some crucial tips for this stage of the pandemic:.

  • Avoid catching COVID-19 because while the Omicron variant dominates, the more severe disease-causing Delta variant is still around.
  • Get vaccinated. COVID-19 vaccines and boosters protect against hospitalization with Omicron. (https://www.nytimes.com/2022/01/21/health/cdc-covid-booster-omicron.html).
  • Get tested regularly. The testing strategy in Vienna is excellent – even the Germans think that we’re doing a great job. Take advantage of the testing even when you don’t have symptoms, but especially if you had contact with someone who had COVID-19 or has symptoms. You need to register with “Alles Gurgelt”, and you can pick up eight tests per month.
  • Treat your ‘Schnupfen’ – sniffles or sore throat – as if they’re COVID-19, and stay home.
  • If you’re sick with COVID-19, isolate. The isolation time with Omicron is a bit reduced, because you’re infectious a couple of days before symptoms begin and about three days after symptoms disappear. Still, it’s best to have a negative COVID-19 test before leaving isolation.
  • Continue physical distancing (at least 1 meter) and avoid poorly ventilated and crowded spaces. Open windows to improve ventilation indoors.
  • Wear an N95 mask over your mouth and nose, where Omicron is abundant. In Austria, we are exceptionally fortunate because there is a sufficient supply of these masks. Use clean hands to put on and remove your mask carefully.
  • Wash your hands regularly and, as always, don’t touch your face.
Dr. Michelle Epstein
Dr. Michelle Epstein
Michelle Epstein is a medical doctor graduated from the University of Alberta in Canada, who has specialised in Internal Medicine at the University of British Columbia and Allergy and Clinical Immunology at Yale University. Since 2004, she has been a Lab Leader at the Medical University of Vienna’s Division of Immunology.

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