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Cambridge sees 42 percent ‘breakthrough’ COVID cases

People crossed Broadway Street in Cambridge on Thursday as the city is reporting a rise in new COVID-19 cases.Matthew J. Lee/Globe staff

City officials in Cambridge are reporting a rise in new COVID-19 cases and are urging residents, whether they are vaccinated or not, to wear masks and practice social distancing “where transmission is likely and when around unvaccinated people, including young children.”

There have been 83 confirmed and probable cases reported in Cambridge so far in July, the city said in a statement Wednesday, with 42 percent of those cases, known as “breakthrough” cases, among people who are fully vaccinated.

“With 19 new cases being reported yesterday, it’s clear this #DeltaVariant is on the rise, and we need to be very cautious,” Cambridge Vice Mayor Alanna Mallon wrote in a tweet Thursday.


The uptick in Cambridge comes as state and local health officials wrestle with a surge in cases on the Cape and Islands, particularly in Provincetown where a cluster grew to 256 confirmed cases on Tuesday. Among those who tested positive for the coronavirus, 190 are Massachusetts residents and 109 live in Barnstable County.

On Wednesday, Nantucket’s Health and Human Services department issued an advisory asking residents and visitors to wear face masks indoors in public locations when they cannot be physically distanced from others.

Officials in Boston are also reporting an increase in new daily cases, but the numbers have not reached a level to cause major concerns.

Cambridge officials continue to encourage residents to get vaccinated while noting that the vaccines are not guaranteed to prevent infection but can help protect against severe symptoms. About 67 percent of residents were fully vaccinated as of July 15, and 73 percent of residents had received at least one dose, according to the city’s COVID-19 data center.

“Even among people with breakthrough infections, the vaccines have proven to be extremely effective at preventing serious illness and death,” Cambridge officials said in the statement. “It is important to remember that no vaccine offers 100% protection against illness.”


Updated vaccination data is expected to be released by the state later Thursday.

Health officials in neighboring communities are also reporting a rise in cases.

In Boston, a total of 208 new cases were reported last week, up from 62 cases the week before, according to data from the Boston Public Health Commission. As of Wednesday, there have been 210 positive cases this week.

The city was reporting a daily average of 38.6 new cases as of July 17, a sharp increase from July 3 when the average was just nine new cases per day, according to Marty Martinez, the city’s chief of health and human services.

“We do think some of what we’ve seen in recent weeks is coming out of the Fourth of July holiday when more people were getting together in groups,” Martinez said. “And the weather was bad [during the holiday weekend] so more people probably gathered indoors than we probably would have liked.”

None of the city’s metrics used for monitoring the virus are above the “thresholds of concern” outlined by the city, he said.

Martinez said the goal is to stay below 67 positive tests per day, which is still well below the threshold of about 340 cases per day. He said the city passed that threshold in the spring of 2020 and “several times” during the winter surge.

Nearly 60 percent of Boston residents had been fully vaccinated as of July 13, a total of 405,670 people, the city said in a tweet Thursday. About 66 percent of residents had received at least one dose of a coronavirus vaccine as of July 13, Martinez said.


“I’m feeling good about the progress we’ve made and there is still more work to be done,” he said, noting a gap in vaccination rates among young people and between racial and ethnic groups.

In Boston, 44 percent of Black residents and 46 percent of Latinx residents have been fully vaccinated. Asian and Pacific Islander residents are the highest vaccinated group at 73.4 percent as of July 13, and 60 percent of white residents are vaccinated, according to the city’s data. The vaccination rate for Native Americans in the city was 34 percent.

Martinez said 60 percent of cases are among people between ages 28 and 39, which is “higher than it has been throughout the pandemic.”

“We still need younger Bostonians to get vaccinated,” he said.

Martinez said the department is also focused on increasing vaccinations in Mattapan, where 39.9 percent of residents were fully vaccinated as of July 13, the lowest rate among Boston neighborhoods. The South End had the highest vaccination rate at 72.5 percent, according to the city’s data.

Somerville has seen a slight bump in new cases, according to Doug Kress, the city’s Health and Human Services director.

“We weren’t seeing many pop up and were having days with zero new cases, but as of late we’re seeing a little bit of an uptick with four to seven cases per day,” Kress said. “We’re keeping an eye on this. We’re also seeing an increase in the people who want to be tested, whether that is because they were exposed or they heard about the Delta variant.”


About 71 percent of Somerville residents were fully vaccinated as of July 13, according to data on the city’s website.

Nick Stoico can be reached at nick.stoico@globe.com. Follow him on Twitter @NickStoico.