what is the delta variant
Here’s everything you need to know about the Delta variant, why it’s so contagious, and whether COVID-19 vaccines can protect against infection

The Delta variant is a highly contagious strain of the coronavirus (SARS-CoV-2) that caused COVID-19. Also known as B.1.617.2, documented samples of this variant were first isolated in India in October 2020, although the first case wasn’t diagnosed until December 2020. 

Since the diagnosis of the first Delta variant case in the United States in March 2021, it has emerged as the dominant strain in the country. Data from the CDC reveal that by the end of July, the Delta variant will account for over 80% of the COVID-19 cases.

Why is the Delta variant so contagious?

All viruses, including SARS-CoV-2, tend to mutate over time, meaning their genetic makeup undergoes changes. Although most of these genetic changes don’t affect the characteristics of the virus, some cause concern when they alter viral properties, such as:

  • Infectivity or ease of spread
  • Disease severity, including mortality
  • Diagnostic tests
  • Vaccine efficacy
  • Response to treatment

The Delta strain has high rates of transmission due to a change in the spike protein. Mutations on the protein make it easier to infect human cells, meaning that the strain is highly contagious and easily spread.

Due to its high infectivity, the Delta variant has raised concerns about the possibility of accelerating the pandemic. Studies so far suggest that the Delta variant is spreading 50% faster than the Alpha variant. Also, it has a 50% higher rate of transmission than the original strain of SARS-CoV-2.

What are symptoms of the Delta variant?

Symptoms of the Delta variant infection are similar to those caused by other variants, although some studies suggest that the Delta variant may cause slightly different dominant symptoms than the original COVID-19 strain. 

According to reports in the U.K., predominant COVID-19 symptoms, such as loss of smell and persistent cough, are less common with the Delta variant. More common symptoms seem to be:

There are, however, no symptoms specific to the Delta strain.

Do vaccines protect against the Delta variant?

Vaccines are still the best protection against the different COVID-19 variants, including the Delta variant. The vaccines available in the US are safe and highly effective in protecting you from infection.

You are considered fully vaccinated if at least 2 weeks have passed since you received either of the following:

  • Second dose of the Pfizer or Moderna vaccine
  • First (and only) dose of Johnson & Johnson's (J&J) vaccine

Do I need to wear a mask even if I am fully vaccinated?

Even if you are fully vaccinated, it is best to wear a mask and follow other safety precautions, including social distancing and hand washing, especially in crowded areas.

Infections in vaccinated people are rare but not impossible. Studies are still underway to determine how long the vaccines offer protection against infection after the person is fully vaccinated. The World Health Organization (WHO) has therefore recommended that vaccinated individuals mask up again because of the new Delta variant. No such recommendations, however, have been made by the CDC. 

According to the CDC, people with weakened immune systems, including people who take immunosuppressive medications, may not be protected even if fully vaccinated. However, so far vaccines still offer the best protection against COVID-19, so anyone who is eligible for the vaccine should get vaccinated.

Is the Delta variant more deadly?

Studies so far do not suggest with certainty that the Delta variant causes more severe infection or increases hospitalization rates compared to the previous variants. 

More studies are underway to confirm whether there are any changes in the disease severity caused by this strain. However, some studies have suggested that the disease is more severe among unvaccinated individuals.

Is the Delta variant the same as the Delta Plus variant?

The Delta Plus variant (also called B.1.617.2.1 or AY.1) is considered a subvariant of the Delta variant. This variant has an additional mutation in the spike protein the virus uses to enter human cells, called K417N, allowing the virus to better attack lung cells. Most properties of this virus are similar to the Delta variant.

Although the Delta Plus variant has now been found in multiple countries including the U.S. both the WHO and CDC have not yet labeled the variant a concern.

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Medically Reviewed on 7/26/2021
References
Centers for Disease Control and Prevention. SARS-CoV-2 Variant Classifications and Definitions. https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-info.html

Katella K. 5 Things to Know About the Delta Variant. Yale Medicine. https://www.yalemedicine.org/news/5-things-to-know-Delta-variant-covid

World Health Organization. Tracking SARS-CoV-2 Variants. https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/