24 vaccinated friends had a blowout vacation on Cape Cod. Though their symptoms were mild, 14 of them caught COVID-19, report says.

• 24 fully vaccinated friends had a week-long July 4 getaway in Provincetown, Massachusetts.
• 14 of those caught COVID-19, in spite of being fully vaccinated.
• The cases are part of a bigger study that prompted the CDC to change its indoor masking guidance.

Fourteen of 24 vaccinated friends who visited the Cape Cod town of Provincetown, Massachusetts in July caught COVID-19, Bloomberg reported on Sunday, an anecdote showing the limits of vaccination.

The group went to the beachside town for a weeklong getaway around July 4, Bloomberg reported.

Daniel Barefoot was one of this group. The 33-year-old lawyer living in Washington realized that he had caught COVID-19 when he couldn't taste a piece of candy when he got home, he told Bloomberg.

Of the 14 friends who tested positive for COVID-19, none were seriously ill, per the report.

Provincetown was home to a large outbreak among vaccinated people

The friends were not the only ones to be infected. About 60,000 people visited the LGBTQ-friendly town around the July 4 weekend.

There were conga lines, drag brunches, and house parties, The New York Times reported, which appear to have aided the spread of the virus.

Bloomberg reported that Barefoot and his friends found long lines, packed dance floors, and tight crowds during their breaking - but felt reassured by the high levels of vaccination there.

But it wasn't enough to stop an outbreak, albeit one where hardly anyone felt the worst symptoms of COVID-19, which rarely hospitalizes or kills vaccinated people but does so far more often to the unvaccinated.

The Provincetown outbreak prompted the city to reinstate indoor mask mandates on July 25, and piqued the interest of the Centers for Disease Control and Prevention (CDC).

In a study released Friday, the CDC tracked 469 cases among Massachusetts residents who visited the town.

They found that 74% of those were fully vaccinated. An overwhelming majority of the cases were caused by the Delta variant, the study reported.

But because vaccines greatly reduce the risk of severe disease, only four of those who were vaccinated were hospitalized. None died.

Of those who reported symptoms, the most common were mild, and included coughing, a sore throat, and fever.

Infection among vaccinated could be a breeding ground for mutations

The breakthrough in Massachusetts prompted the CDC to update its guidance for vaccinated people.

Last week, the CDC recommended that all people wear masks indoors as the Delta variant spreads through the country, including those fully vaccinated.

"Some vaccinated people infected with the Delta variant after vaccination may be contagious and spread the virus to others," Dr Rochelle Walensky, the CDC Director, said last week.

The guidance is aimed at protecting those who are not vaccinated, NIH chief Francis Collins said Sunday.

But it has another purpose: it limits widespread infection among vaccinated people, which could lead to the virus developing mutations against the vaccine, as reported by Insider's Aylin Woodward and Hilary Brueck,

The virus is "just a few mutations potentially away" from evading vaccines totally, Walensky said on Tuesday.