Coronavirus: Most infected in outbreak after large public events were fully vaccinated, CDC says

The Centers for Disease Control and Prevention on Friday released new data which showed that a majority of people infected with COVID-19 in a recent outbreak in Massachusetts were fully vaccinated.

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The data, taken from COVID-19 cases reported in July in an unidentified town in Barnstable County, was released after an internal CDC document was leaked which showed that the delta variant of the virus can be spread from fully vaccinated people at the same rate as from unvaccinated people.

In July, officials identified 469 cases of COVID-19 associated with summer events and large public gatherings in Barnstable County. Nearly three-quarters of those infections (346) were detected in people who were fully vaccinated, according to the data.

>> Related: Leaked CDC report: Delta variant as contagious as chickenpox

About 79% of the vaccinated patients who had breakthrough infections experienced some symptoms, including four people who were hospitalized. One unvaccinated person was also hospitalized. No deaths were associated with the outbreak.

The highly transmissible delta variant, which has been driving up infection rates nationwide in recent weeks, accounted for about 90% of the 133 infections which underwent genomic sequencing, the data showed.

On Tuesday, CDC Director Dr. Rochelle Walensky said “new science related to the delta variant” prompted an update of guidance on mask wearing. Officials recommended that fully vaccinated people resume wearing masks indoors in areas where COVID-19 is spreading widely two months after announcing that fully vaccinated people would no longer need to wear masks.

>> Related: Coronavirus: CDC recommends masks indoors for some vaccinated people

In the report released Friday, officials said that in light of the new data, officials in all jurisdictions – not just those with high COVID-19 transmission rates – “might consider expanding prevention strategies, including masking in indoor public settings regardless of vaccination status.”

Officials with the Massachusetts Department of Public Health noted a spike in COVID-19 cases in Barnstable County as multiple summer events were held between July 3 and July 17. On July 3, officials said the 14-day average of COVID-19 cases reported in the town in Barnstable County was zero per 100,000 people per day. By July 17, that number had risen to 177 cases per 100,000 people per day.

>> Read the full report from the CDC

“Unlike with other variants, vaccinated people infected with Delta can transmit the virus,” Walensky said Friday in a statement. “This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation. The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones.”

>> Related: How do you know if you have the delta variant; what are the symptoms?

As of Thursday, about 50% of Americans, or 164.1 million people, have been fully vaccinated, according to the Centers for Disease Control and Prevention. Since the start of the pandemic, officials have confirmed more than 34.7 million infections and reported more than 612,000 deaths nationwide, according to numbers compiled by Johns Hopkins University.

More than 196.9 million COVID-19 cases have been reported worldwide, resulting in 4.2 million deaths, according to Johns Hopkins.

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