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The Delta Variant: What You Need to Know

An Infectious Disease Specialist Discusses the Dangers of the More Transmissible Coronavirus Variant and the Best Way to Protect Ourselves

image of viruses

The spread of the Delta variant has put countries around the world on high alert. South Africa has imposed curfews and bans on gatherings; Bangladesh has shut down public transportation; parts of Australia are under stay-at-home orders and mask mandates. According to the European Centre for Disease Prevention and Control, the Delta variant is on track to make up 90 percent of new cases of COVID-19 in the European Union by the end of August. And the Delta variant has overtaken the Alpha variant as the dominant variant in the United States, according to estimates released by the Centers for Disease Control and Prevention (CDC).

“Delta currently accounts for about 51 percent of U.S. COVID-19 cases and is the variant that is increasing the fastest throughout the country,” says Dr. Roy M. Gulick, chief of the Division of Infectious Diseases at NewYork-Presbyterian/Weill Cornell Medical Center and Weill Cornell Medicine.

Dr. Gulick spoke with Health Matters about the Delta variant — the danger it poses, why it’s more transmissible, and how we can defeat it.

Dr. Roy Gulick

Dr. Roy Gulick



Health Matters: What is the Delta variant?
Dr. Gulick: Like other viruses, coronaviruses, including SARS-COV-2, the virus that causes COVID-19 can change (or mutate) over time. This leads to different viral variants, and these have emerged in different parts of the world. The variants originally were named for their place of origin and with letters and numbers, but the World Health Organization now names them with Greek letters.

The Delta variant was originally called B.1.617.2 and was first identified in India in late 2020 and is spreading rapidly throughout the world. It is now the dominant viral strain in the United Kingdom and the U.S.

The CDC has labeled the Delta variant as a “variant of concern.” What does that mean?
SARS-COV-2 variants can have different properties than the original virus. Variants of concern are those viruses that can be transmitted between people more easily, cause worse COVID-19 illness, are less susceptible to antibodies resulting from natural infection or vaccination, are less susceptible to COVID-19 treatment or prevention strategies, or are more difficult to detect.

The Delta variant appears more transmissible and may be associated with more severe COVID-19 illness, so this could lead to another COVID-19 surge in unvaccinated populations.

What makes a variant more transmissible?
Some viral variants can grow better in human cells and make greater quantities of the virus — the higher levels of virus can increase the efficiency of transmitting to other people. The Delta variant is about 50 percent to 60 percent more transmissible than the original virus.

Do the vaccines offer protection against the Delta variant?
Full vaccination with the mRNA vaccines (Pfizer and Moderna) protect well against the Delta variant and the other common variants. (In fact, a recent study found that two doses of the Pfizer vaccine were 88 percent effective at protecting against symptomatic disease caused by Delta.) The Johnson & Johnson vaccine has not yet been tested, but likely also offers protection, though possibly at a lower rate.

How do we stop the Delta variant from spreading?
Vaccines are the best tool we have to end the COVID-19 pandemic. People who can’t get vaccinated or don’t respond to vaccinations (for example, people with compromised immune systems) should continue to wear a mask, wash their hands, and practice social distancing.

The World Health Organization and Los Angeles County health officials recently recommended that vaccinated people should continue to wear masks indoors. This is a reaction to the increasing spread of the Delta variant throughout the world. And after declining for weeks, U.S. COVID-19 cases are increasing again, mostly in western and southern states with low vaccination rates.

Viral variants occur when the virus is transmitted and reproduces itself. COVID-19 vaccines are key to controlling the pandemic and to prevent future variants from developing. Current vaccines are highly effective and not only prevent infection, but they also effectively reduce transmission to others.

This story was first published by NYP's Health Matters.

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