What Distinguishes Omicron Variants From Other Variants?

Although new variants are an expected part of the evolution of viruses, monitoring each one that surfaces is essential in ensuring we—in the U.S. and globally—are prepared. This is especially true if a new variant is more aggressive, highly transmissible, vaccine-resistant, able to cause more severe disease—or all of the above, compared with the original strain of the virus.

The World Health Organization (WHO) names new coronavirus variants using the letters of the Greek alphabet, starting with the Alpha variant, which emerged in 2020.

Omicron and Other Variants

1. Omicron and BA.2

There’s still a lot to learn about Omicron (BA.1) and its subvariant, BA.2, which surpassed the original Omicron strain in March to become the predominant variant in the U.S. Omicron was first identified in Botswana and South Africa in late November 2021, and cases quickly began to surface and multiply in other countries. The BA.2 subvariant appears to spread more easily than its predecessor, but while experts are following emerging data to learn more, it does not appear to cause more severe disease than BA.1. 

How contagious is it? Omicron is more transmissible than Delta was—very early reports from South Africa showed cases rising rapidly from 300 a day to 3,000 a day over a two-week period. This likely helped it become the predominant variant in most places. More than 30 of Omicron’s mutations are on the virus’s spike protein, the part that attaches to human cells, and several of those are believed to increase the probability of infection. So, part of its enhanced transmissibility may come from its ability to evade some immune responses, especially in individuals who were previously infected but not vaccinated. 

Severity: Though Omicron has caused record numbers of cases, the variant appears to be less severe than previous variants. A Certain Report shows that factors such as lengths of hospital stays, ICU admittance, and death were “lower than during previous pandemic peaks.” 

Can vaccination prevent it?  The CDC says getting vaccinated and staying up to date with your vaccine and a booster shoot is the best protection against Omicron. 

2. Delta

Delta (B.1.617.2) was first identified in India in late 2020; it soon spread throughout the world, becoming what was the predominant version of the coronavirus—until Omicron took its place in mid-December. 

How contagious is it? It’s estimated that Delta caused more than twice as many infections as previous variants—in Connecticut, it was estimated to have been 80 to 90% more transmissible than the Alpha variant. In the U.S., in June 2021, after a steady decline in COVID-19 cases and hospitalizations, the arrival of Delta coincided with a rapid reversal of that trend. In the fall of 2021, there were surges even in the most vaccinated states, prompting experts to urge people to get their booster shots.

Severity: Delta caused more severe disease than other variants in people who weren’t vaccinated. Early studies from various places suggested Delta was more likely to result in hospitalization in the unvaccinated. A report showed that this past summer found that people in England had double the hospitalization risk with Delta than they did with Alpha, the previously dominant variant in that country. 

Can vaccination prevent it? All three vaccines in the U.S. were considered highly effective against severe illness, hospitalizations, and death from Delta. No vaccine is 100% effective, and Delta caused breakthrough infections in some fully vaccinated people. Also, infected vaccinated people could spread the virus to others, although likely they were infectious for a shorter time.

3. Beta

This variant, or B.1.351, was identified in South Africa at the end of 2020 and spread to other countries. Experts had been concerned about its several mutations and its potential to evade antibodies. Beta was not common in the U.S.

How contagious is it? The experts said Beta was about 50% more contagious than the original coronavirus strain.

Severity: There was evidence to suggest that Beta may have been more likely than other variants to lead to hospitalization and death.

Can vaccination prevent it? South Africa stopped offering the AstraZeneca-Oxford vaccine early in 2021 after clinical trials showed it did not provide strong protection against mild and moderate disease from the Beta variant.

4. Alpha

Alpha (B.1.1.7) was the first of the highly publicized variants. Alpha first appeared in Great Britain in November 2020 and infections surged in December of that year. It soon surfaced around the world and became the dominant variant, where the experts classified it as a variant of concern. Then, Alpha faded away with the rise of the more aggressive Delta variant.

How contagious is it? Some mutations in Alpha’s spike protein were thought to make it more infectious. The B.1.1.7 lineage was believed to be 30 to 50% more contagious than the original SARS-CoV-2 strain. 

Severity: Studies have suggested the B.1.1.7 lineage was more likely to land infected people in the hospital and was deadlier than the original virus.

Can vaccinations prevent it? Pfizer, Moderna, and Johnson & Johnson all said their vaccines were effective in preventing severe disease and hospitalization in Alpha cases. 

Conclusion

The experts are currently focused on Omicron as a variant of concern in the world. The classification is given to variants that show increased transmissibility, could cause more severe disease, may be resistant to antibodies from previous infections or vaccination, and/or show an ability to evade diagnostic detection.

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