Main Variants:

Alpha (B.1.1.7)

The Alpha COVID-19 variant was first identified in Great Britain in November 2020. The variant’s lineage was believed to make it 30 to 50% more contagious than the original strain of COVID-19. Studies have shown that the Alpha variant is more fatal and more severe to those who contract it, as compared to the original strain of COVID-19, but Moderna, Pfizer, and Johnson & Johnson vaccines have all said their vaccines are effective in preventing severe cases of the variant. According to a study from the Center for Disease Control (CDC) released in June, by mid-April of 2020, 66% of cases in the United States were from the Alpha variant. 

Beta (B.1.351)

The Beta variant of COVID-19 was first discovered in South Africa. According to the CDC, the Beta variant is said to be almost 50% more contagious than the original COVID-19 strain. There is also some evidence that the Beta variant is more likely to lead to hospitalization and death than other variants. Vaccines against this variant have been less effective, as companies like Pfizer, Moderna, and Johnson & Johnson have reported that their vaccines have been shown to offer less protection against this variant. The AstraZeneca-Oxford vaccine, which is not available in the United States, was shown to not be protective against cases of the Beta variant in a 2021 clinical trial. 

Delta (B.1.617.2)

The Delta variant, which was first identified in India, might spread more easily than previous variants, according to the CDC. The variant also may cause more serious and severe cases than other variants, resulting in a higher chance of hospitalization. With the Delta variant, people who are fully vaccinated could still become infected. These kinds of infections are known as “breakthrough infections.” However, vaccines are still effective at preventing severe illness and death, even though some early studies show that fully vaccinated people can still spread the variant to others. 

Omicron (B.1.1.529)

The Omicron variant was also first discovered in South Africa, and may spread more easily than other variants, according to the CDC. Omicron might be less severe than previous variants, and infections might be more mild. However, since this variant is relatively new, not much can be definitively said about its severity and mortality rate. Breakthrough infections are still possible with this variant, and fully vaccinated individuals are still able to spread the virus to others. 

Gamma

The Gamma variant was first detected in Brazil. According to the Global Virus Network, the P1 version of the Gamma variant is up to 2.5 times more transmissible than the original COVID-19 virus. However, the variant is most likely not as lethal as other variants, although additional studies are needed to verify this. The variant is not listed as a variant of concern on the CDC website. 

Sources:

https://www.cdc.gov/coronavirus/2019-ncov/variants/about-variants.html

https://www.yalemedicine.org/news/covid-19-variants-of-concern-omicron

https://gvn.org/covid-19/gamma-p-1/