Jul 30, 2021 - Health

CDC: Delta variant may cause mild COVID among fully vaccinated people

A storefront sign reminds people masks are for everyone on July 19, 2021 in Los Angeles, California.
A storefront sign in Los Angeles reminds people masks are for everyone. Photo: Frederic J. Brown/AFP via Getty Images

About 74% of 469 COVID-19 cases associated with large gatherings held in Barnstable County, Mass., from July 3 to 17 were among fully vaccinated people, according to data released Friday from the Centers for Disease Control and Prevention.

Why it matters: The data bolsters emerging evidence that vaccinated people have high viral loads and may transmit the Delta variant as easily as those who are unvaccinated.

Be smart: Despite mild breakthrough cases appearing more common than previously thought, "vaccination is the most important strategy to prevent severe illness and death," the report emphasizes.

The big picture: Presentation slides from the agency leaked Thursday night showed that unpublished research indicated that the Delta variant causes more severe illness in unvaccinated people and spreads as easily as chickenpox.

  • On Tuesday, the CDC recommended people should wear masks in indoor public settings in areas where COVID-19 transmission is high or substantial regardless of vaccination status.

What they found: Among the vaccinated with a breakthrough infection in Barnstable County, nearly 80% reported mild signs or symptoms, with the most common being cough, headache, sore throat, myalgia and fever.

  • The people reported being in densely packed indoor and outdoor events at venues that included bars, restaurants, guest houses and rental homes.
  • Five people were hospitalized, including one patient, who was middle-aged, unvaccinated, and had multiple underlying medical conditions. The remaining four adults were fully vaccinated, varied in age and, two had underlying medical conditions.
  • As of July 27, no deaths were reported.
  • A majority of the cases occurred in men with a median age of 40, but is likely due to the health department's sampling from the public events, which were marketed to adult male participants.

What they're saying: "This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation," CDC director Rochelle Walensky said in a statement Friday.

  • "The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones," she added.
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