The COVID-19 Delta Variant: What to Know

The highly transmissible COVID-19 delta variant, also known as B1617.2, was found in India in October 2020. It was the dominant strain in the U.S. and several other countries during the fall of 2021. 

What to Know

It spreads quickly. As of January 1, 2022, the delta variant has reached more than 183 countries. It’s already overtaken the alpha variant in number of cases in many of those countries, including the U.S. The variant is thought to be 55% to 90% more transmissible than previous COVID-19 variants. Experts believe delta is anywhere from 30% to 100% more infectious than alpha.

Researchers are still unsure why the delta variant is so much more transmissible than others. They think changes in the variant’s protein might make it easier to enter human cells. Another early study suggests that a mutation in the delta variant might help it blend better with human cells once it attaches itself. If it can easily blend with your cells, it’s able to infect more of them and overpower your immune system.

It seems to affect younger people more often. In the United Kingdom, studies showed that children and adults under 50 were 2.5 times more likely to become infected.

Symptoms appear to be more severe and happen faster. People may be more likely to end up in the hospital if they have the delta variant. Studies suggest it might have almost double the risk of hospitalization than the alpha variant.

In China, doctors say patients with the delta variant are sicker than those they treated early in the pandemic. And their condition seems to go downhill much faster.

Data from the Zoe COVID Symptom Study, an app that allows people to track symptoms, shows COVID-19 symptoms in the United Kingdom may be changing as the delta variant spreads. 

Top symptoms reported on the app include:

A cough is becoming less common and loss of smell is no longer listed in the top 10 common symptoms anymore. Researchers are concerned people may mistake symptoms for a bad cold and avoid quarantine, helping the variant spread.

How to Protect Yourself

Getting vaccinated is your best bet. Reports suggest two doses of the Pfizer-BioNTech vaccine provides 79% protection against delta variant infection. It seems to be 96% effective against hospitalization if infected.

Two doses of the AstraZeneca vaccine are 92% successful in stopping hospitalization due to the delta variant. And no deaths have been reported among those vaccinated.

WebMD Medical Reference Reviewed by Michael W. Smith, MD on June 18, 2021


World Health Organization: Tracking SARS-CoV-2 variants

GISAID: hCoV-19 Tracking of Variants

Gavi Vaccine Alliance: "Five things we know about the Delta variant (and two things we don't)"

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