How Do the COVID-19 Variants Differ? Delta Variant

Medically Reviewed on 12/15/2021
How Do the COVID-19 Variants Differ
The Delta variant is believed to be twice as contagious as previous variants and is associated with increased rates of hospitalization and serious illness

Multiple variants of the SARS-CoV-2 coronavirus have been emerging that are different from the original Alpha variant. 

The Delta variant is believed to be twice as contagious as previous COVID-19 variants and is associated with increased rates of hospitalization and serious illness, especially among those who are unvaccinated. Breakthrough infections are also common, even though they are typically mild.

A study from China reported that people infected with the Delta variant can carry as much as 1,000 times the viral load as those infected with the original COVID-19 virus.

Preliminary studies suggest that some of the new variants seem to attach more tightly to human cells, which increases their ability to get transmitted more easily. There are additional Delta variants, including Delta Plus, which have been found in some countries including the United States, United Kingdom, and India. Research is still underway to determine the exact extent of its virulence and transmissibility.

Different variants have emerged in other countries as well, some of which are more infectious than others. For example, the Omicron variant, which first appeared in South Africa, is likely to reinfect even people who have recovered from previous COVID-19 variants.

Why are there so many COVID-19 variants?

Viruses mutate over time due to genetic changes, and RNA viruses in particular have a high mutation rate. Thus, the coronavirus continues to evolve and change gradually. 

Because of geographical differences, the virus mutates differently according to region and gives rise to different COVID-19 variants.

Variant of concern vs. variant of interest vs. variant of high consequence

The WHO and the CDC have classified the COVID-19 variants into three categories.

  1. Variant of interest: A variant of interest is a coronavirus variant that has genetic features that predict greater transmissibility, ability to escape detection in diagnostic tests, ability to evade natural immunity, or ability to cause more severe disease compared to earlier forms of the virus.
  2. Variant of concern: A variant of concern is one that has the ability to cause more infections, breakthroughs, or reinfections in those who are vaccinated or previously infected. These variants are more likely to escape diagnostic tests, cause severe disease, or resist antiviral therapy. Alpha, Beta, Gamma, and Delta variants of the COVID-19 virus are classified as variants of concern.
  3. Variant of high consequence: A variant of high consequence is a variant for which available vaccines do not offer protection. Currently, there are no variants of high consequence.
Medically Reviewed on 12/15/2021
Image Source: iStock Images

Centers for Disease Control and Prevention. What You Need to Know About Variants.

UpToDate. SARS-CoV-2 Variants of Concern.

Wilson FP. Omicron: What the Data Really Show. Medscape.

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Li B, Deng A, Li K, et al. Viral infection and transmission in a large well-traced outbreak caused by the Delta SARS-CoV-2 variant. MedRxiv. Jan 1, 2021.