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5 Things to Know About the Delta Variant

For many, this summer has marked a return to normal. But COVID-19 is still circulating in the United States, and a new strain — largely impacting unvaccinated people — is gaining ground. Here’s what you need to know about it:

1. The Delta variant is more contagious than other COVID-19 strains

The Delta variant is a highly contagious mutation of SARS-CoV-2 and experts have found it to be twice as contagious as the original strain. Recent estimates from the CDC show the Delta variant now accounts for more than 51% of COVID-19 cases in the United States, making it the dominant variant. Last month it was classified as a “variant of concern” by the CDC. The CDC defines “variants of concern” as having increased transmissibility, increased disease severity, or reduced effectiveness of treatments or vaccines.

2. Unvaccinated people are most at risk

In May, the Cleveland Clinic reported that 99 percent of new cases and COVID-19-related hospitalizations were people who were not fully vaccinated. This is especially important as patients infected with the Delta variant are twice as likely to be hospitalized.

In a local news article, Mark Steele—chief clinical officer of Truman Medical Centers, University Health—reported that all of their current hospitalized COVID-19 patients are not vaccinated against COVID-19. Additionally, COVID-19 cases are spiking in southwest and northern Missouri, where vaccination rates are low.

3. COVID-19 vaccines provide strong protection against Delta

After two doses, the Pfizer COVID-19 vaccine is 80 percent effective at preventing infection, 88 percent effective at preventing symptomatic disease, and 96 percent effective at preventing hospitalization from the delta variant. The Moderna vaccine uses the same technology as Pfizer and has shown similar rates of overall effectiveness.

The single-shot Johnson & Johnson vaccine generates a strong antibody response against the Delta variant and other prevalent COVID-19 variants.

4. Delta won’t be the last variant to arise

Continued transmission of COVID-19 and spread throughout the community drastically increases its chances of a mutation similar to the delta variant. If we break the cycle of transmission and decrease the number of infections in a community we can curb new variants from forming. Vaccination helps both to prevent COVID-19 infection and to keep new variants from developing.

5. Be vigilant, not alarmed 

While the delta variant is concerning, there are still many ways community members can protect themselves.

  • Get vaccinated against COVID-19 if you haven’t already. COVID-19 vaccination offers the best protection against all COVID-19 variants. Visit to find local vaccination clinics.
  • If you’re due for your second dose, make a plan to receive it as soon as possible. Getting both doses maximizes your protection against all COVID-19 variants.
  • If you’re not fully vaccinated, continue wearing a mask and social distancing.
  • Whether you’ve been vaccinated or not, get tested for COVID-19 if you’re feeling sick. Find testing opportunities at
  • Stay up-to-date on case rates in your community. View Eastern Jackson County COVID-19 data here.
  • If you have any questions about COVID-19, the COVID-19 vaccine, or the delta variant, reach out to your local health department or your primary care provider.
  • The World Health Organization — citing the rise of Delta, the dearth of vaccines, and high rates of community transmission in many parts of the world — has encouraged fully vaccinated people to continue wearing masks.



Yale Medicine