CDC examine reveals 74% of individuals contaminated with the Massachusetts Covid outbreak had been totally vaccinated

Boston EMS medics work to assist a patient on the way to the ambulance amid the coronavirus disease (COVID-19) outbreak in Boston, Massachusetts, Jan.

Brian Snyder | Reuters

About three-quarters of the people infected with Covid-19 in a Massachusetts outbreak were fully vaccinated against the coronavirus, with four of them ending up in hospital, according to new data released Friday by the Centers for Disease Control and Prevention were published.

The new data, published in the US agency’s Morbidity and Mortality Weekly Report, also found that fully vaccinated people who become infected carry just as much of the virus in their noses as unvaccinated people and could pass it on to other people.

“This finding is worrying and was a key discovery that led to the CDC’s updated mask recommendation,” said CDC Director Dr. Rochelle Walensky in a statement. “The masking recommendation has been updated to ensure that the vaccinated public does not unwittingly pass the virus on to others, including their unvaccinated or immunocompromised loved ones.”

On Tuesday, the CDC reversed course and recommended fully vaccinated Americans living in areas with high rates of Covid infection return to wearing face masks indoors. According to a CNBC analysis, the guidelines cover about two-thirds of the US population.

While the Delta variant continues to hit unvaccinated people the hardest, some vaccinated people could carry higher amounts of the virus than previously thought and potentially transmit it to others, Walensky told reporters when he called on Tuesday. She added that the variant “behaves uniquely differently from previous virus strains”.

A CDC document reviewed by CNBC warned that the delta variant, widespread across the country, is as contagious as chickenpox, has a longer transmission window than the original Covid strain, and can make the elderly sicker even when fully vaccinated.

Delta, now in at least 132 countries and already the predominant form of the disease in the United States, is more commonly communicable than the common cold, 1918 Spanish flu, smallpox, Ebola, MERS and SARS, according to the document. Only measles seem to spread faster than the variant.

The data released on Friday was based on 469 cases of Covid related to multiple summer events and large public gatherings in July in Barnstable County, Massachusetts, according to the CDC. The events took place in an unnamed town in Barnstable, which encompasses Cape Cod and is just outside Martha’s Vineyard. Approximately three quarters or 74% of the cases occurred in fully vaccinated individuals who had completed two-dose treatment with the mRNA vaccines or received a single dose of Johnson & Johnson’s.

According to the CDC, a total of 274 vaccinated patients with a breakthrough infection were symptomatic. The most common side effects were cough, headache, sore throat, muscle pain, and fever. Of five Covid patients who were hospitalized, four were fully vaccinated, according to the agency. No deaths were reported.

Tests identified the Delta variant in 90% of the samples from 133 patients.

The CDC of the data has limitations. The agency found that as the population-level vaccination coverage increases, people who are vaccinated are likely to make up a greater proportion of Covid cases. Additionally, asymptomatic breakthrough infections could be underrepresented due to detection errors, the agency said.

The CDC also said the report was “insufficient” to draw conclusions about the effectiveness of the approved vaccines against Covid, including the Delta variant, during this outbreak.