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Graphics: A closer look at the Cape Cod COVID-19 cluster data


A closer look at the recent cluster of COVID-19 cases linked to July celebrations on Cape Cod is shedding light on the risks the Delta variant poses to fully vaccinated people. Provincetown’s town manager has said there are almost 900 cases associated with the cluster. A new report from the Centers for Disease Control and Prevention released Friday zeroed in on the 469 Massachusetts residents involved with the outbreak and made recommendations on how jurisdictions can curb the effects of highly transmissible variants.

Here is what the CDC found:

Most cases involved fully vaccinated people with symptoms

About 74 percent of the cases studied involved fully vaccinated individuals. Of that group, only 4 people (1.2 percent of the total caseload), ages 20 to 70, were hospitalized. Two of them had underlying medical conditions.


About 79 percent of people infected said they had symptoms, which included a cough, headache, sore throat, and fever. No one died.

This doesn’t mean the vaccines aren’t effective against new variants. Friday’s CDC report added that the more people who get vaccinated, the more likely vaccinated people will represent the portion of positive cases.

Most of the cases involved the Delta variant.

Almost all of the positive cases were caused by the Delta variant (B.1.617.2), the report showed. The Delta variant is one of the most troubling coronavirus variants to date, known for being highly transmissible and causing more severe illness than other strains. It’s currently the most common variant in the United States, responsible for more than 82 percent of cases nationwide. Public health officials have advised that vaccines are effective against the variant and prevent death.

All vaccines represented

Breakthrough cases in the Provincetown cluster involved each of the three major vaccines available in the United States, at rates comparable to the statewide distribution of vaccines among fully inoculated people.

Most cases involved travelers

Visitors to Barnstable County accounted for almost 60 percent of the cases linked to Provincetown. In early July, the town held several major tourist events surrounding the Fourth of July holiday.


As people, including the vaccinated, flock to summer events, crowds and lax COVID-19 safety precautions are a concern to health officials. The CDC report concluded that the investigation into the Provincetown outbreak shows that jurisdictions should consider expanding safety protocols against the virus, including mandating masks in indoor settings, regardless of vaccination status.

Vince can be reached at vince.dixon@globe.com. Follow him @vince_dixon_.