From Omicron to Delta to Mu, learn about the COVID-19 variants being tracked by the CDC. We break down symptoms, transmissibility, vaccine effectiveness, and more.
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Omicron. Delta. Alpha. Mu. There's been so many COVID-19 variants since the pandemic started, it's sometimes hard to keep up. Here, we break down the different strains of the coronavirus that parents need to know, including their symptoms, transmissibility, current status, and how they might affect your children. 

How Do COVID-19 Variants Form? 

"Variants are formed when viruses are transmitted in a population," said Mona Amin, D.O., a board-certified pediatrician based in Fort Lauderdale, Florida, in an Instagram Live interview with Parents. Viruses make copies of themselves in a patient's cells, and sometimes, these RNA copies can have "mistakes." The mutated copies can spread throughout a community as a new strain of the virus.

COVID-19 mutations often affect the spike protein, which penetrates host cells to cause infection. Many changes have made the coronavirus more transmissible; this explains the steady rise of infections after the emergence of new strains. Symptoms also tend to differ between the variants.

Vaccination can stop the formation of new variants in the future. That's because vaccines help fewer people get infected, and it becomes "less likely that these mutations will occur in a population," adds Kristina Deeter, M.D., pediatric intensivist and specialty medical officer for pediatric critical care medicine at Pediatrix Medical Group.

Variant Classification from the CDC

The Centers for Disease Control and Prevention (CDC) breaks down variants into categories. From most to least worrisome, these include:

  • Variants of High Consequence (VOHC): With these variants, experts note reduced effectiveness of "prevention measures or medical countermeasures," says the CDC. 
  • Variants of Concern (VOC): These have evidence of increased transmissibility, more severe symptoms, and reduction in effectiveness of vaccines, treatments, or diagnostic detection.
  • Variants of Interest (VOI): Genetic characteristics show the variant might be more infectious, cause more severe disease, or evade immunity or diagnostics. 
  • Variants Being Monitored (VBM): Data concludes that medical countermeasures are effective. These variants circulating in low levels (or not at all) in the U.S., and they don't pose an imminent risk.

The organization isn't currently tracking any VOHC or VOI. But there are two VOC—Omicron and Delta—that have been circulating the U.S. The CDC also lists several VBM, including Alpha, Beta, Gamma, Iota, Mu, and more. 

COVID-19  Variants of Concern

Omicron Variant (B.1.1.529)

Omicron was first detected in southern Africa in November 2021. It quickly began spreading throughout the world, and it's now the dominant strain in the United States. It's led to an uptick in cases and hospitalizations in every state.

Symptoms in Kids: For most people, the Omicron variant resembles a bad cold. According to a December 16 study out of London, the most common symptoms are runny nose, headache, fever, fatigue, and sore throat. Even so, severe illness and death have been reported on rare occasions, especially for unvaccinated people. The incubation period is also shorter than past variants; symptoms appear three to five days after exposure. 

Transmissibility: The Omicron variant has been shown to be more transmissible than previous strains of COVID-19. You can blame its large number of mutations.

Vaccine Effectiveness: While the COVID-19 vaccine still protects against severe illness, hospitalization, and death—especially if you received the booster shot—Omicron tends to cause more breakthrough infections. Preliminary evidence has also shown an increased risk of COVID-19 reinfection with Omicron; that's possibly because the mutations help the virus evade antibodies. Vaccinated individuals can also spread Omicron to others.

​​Delta Variant ( B.1.617.2)

Another variant of concern, the Delta variant was first identified in India in late 2020. It caused a surge of infections in the United States in the summer of 2021, when it overtook the previously dominant variant (the B.1.1.7  Alpha strain from the United Kingdom). 

Symptoms: Some common symptoms of the Delta variant include runny nose, fever, headache, and sore throat. Cough, loss of smell, and gastrointestinal issues can also occur. Also, "some data suggest the Delta variant might cause more severe illness than previous variants in unvaccinated people," says the CDC.

Transmissibility: According to the CDC, Delta was twice as contagious as previous variants. The new Omicron variant is quickly outpacing Delta, however, and it now accounts for most new infections in the U.S.

Vaccine Effectiveness: Full vaccination is more effective against Delta than Omicron, though breakthrough infections are possible. Most people experience mild or asymptomatic breakthrough cases. 

Note: You may have seen the term "Deltacron" in the news lately. This hybrid variant combines characteristics from Delta and Omicron, but experts don't know whether it's actually a threat. 

COVID-19 Variants Being Monitored (VBM)

Alpha: As the first major variant, Alpha appeared in the United Kingdom in November 2020. Experts estimated that it was 30 to 50 percent more transmissible than the original coronavirus strain from Wuhan. Alpha became the dominant COVID-19 strain in the United States before Delta took over in mid-2021.

Beta: This variant was discovered at the end of 2020 in​​ South Africa. But while it's more severe and transmissible than other variants, it hasn't been common in America, according to Yale Medicine

Gamma: The Gamma variant evolved in Brazil in November 2020. It was deemed a variant of concern from the World Health Organization (WHO) in January 2021.

Epsilon: First detected in California, the Epsilon variant was never able to establish a strong foothold in America, partially thanks to the infectious Delta variant overtaking it.

Eta: The Eta variant was found in the United Kingdom and Nigeria in December 2020, but it has been reported in many countries worldwide. It's not seen in high numbers anymore. 

Zeta: This variant led to a Brazilian outbreak in the spring of 2020. It failed to take hold throughout the world. 

Kappa: Experts first found the Kappa variant in India, and it spread to other countries throughout the beginning 2021.  It carries many of the same mutations as the Delta variant, but it hasn't been as severe. 

Iota: After initially being detected in New York City in November 2020, the Iota variant spread to all U.S. states, but it's practically disappeared now. Reports from the CDC determined it didn't lead to more severe disease or breakthrough infections. 

Mu: Mu made headlines last fall; some experts predicted it would overtake Delta because it evaded vaccine immunity. However, that hasn't happened, and the spread fizzled out.

The Bottom Line

Variants happen as viruses evolve over time. To protect yourself from COVID-19 variants—and prevent the emergence of new variants in the future—it's important to get vaccinated and follow all recommended health precautions.