Massachusetts breakthrough coronavirus cases have been rising rapidly in recent weeks amid the more highly contagious delta variant, but the percentage of fully vaccinated people getting infected remains low and the vaccine is “still doing an amazing job at preventing the most severe illness,” infectious disease experts tell the Herald.
Those who are unvaccinated continue to account for a wide majority of new daily COVID-19 cases and hospitalizations in the Bay State, according to data from the state Department of Public Health. This trend continues as unvaccinated people are a minority of the state’s population.
The latest breakthrough case count from the state shows that 6,373 fully vaccinated people have tested positive for the virus out of more than 4.3 million fully vaccinated individuals, or 0.15%.
The 6,373 infections is as of July 24 — a jump of 1,923 cases during the previous two weeks. That averages out to 137 daily infections during those weeks amid the delta variant uptick.
The fully vaccinated cases have been making up about one-third of the state’s overall reported cases as daily infection tallies near 500 on average.
Between July 10 and July 17, the state reported 716 breakthrough infections — a daily average of 102 cases.
Then the following week, officials reported 1,207 breakthroughs — a daily average of 172 breakthrough infections.
The Provincetown coronavirus cluster of about 900 cases occurred during this timeframe — of that outbreak, about 74% of the cases were among fully vaccinated people.
“We know now quite well through various data sources and the Provincetown outbreak that the delta variant is predominant and can lead to breakthrough infections,” said Davidson Hamer, a Boston University specialist in infectious diseases.
“Breakthroughs are more common with delta than previous variants of concern,” he said. “But the proportion of those who are infected is much higher in those who are not vaccinated, and the percentage goes down to a very small proportion for those who are fully vaccinated.”
In the wake of the Provincetown outbreak, the CDC last week updated its guidance for fully vaccinated people, recommending everyone wear a mask in indoor public settings in areas of substantial and high transmission.
The Massachusetts Department of Public Health is advising fully vaxxed people to wear a mask when indoors if they have a weakened immune system, or if they’re at increased risk for severe disease because of their age or an underlying medical condition.
COVID-19 hospitalizations remain at a significantly lower rate for those who are fully vaccinated. There have been 361 hospitalizations among fully vaccinated people, which is 0.008% of those who are fully vaccinated.
The state reported 58 breakthrough hospitalizations during the last two weeks, which is about four hospitalizations each day, or 21% of all COVID-19 hospital admissions. On average, 15 unvaccinated people are being admitted to the hospital each day.
“The most important point is the vaccine is still still doing an amazing job at preventing the most severe illness,” said Todd Ellerin, director of infectious diseases at South Shore Health. “I urge anyone who is unvaccinated to get vaccinated now.”
The state has reported 91 breakthrough deaths, or 0.002% of the more than 4.3 million people who are fully vaccinated.
