Despite the threat posed by breakthrough infections, CDC Director Rochelle Walensky (pictured) and Harvard infectious disease experts were unanimous that transmission still primarily occurs among the unvaccinated.
Last week, the Centers for Disease Control and Prevention confirmed what Harvard-affiliated physicians had reported from anecdotal and laboratory evidence: the Delta variant of COVID-19 not only spreads more rapidly than other versions of the virus, it can sicken vaccinated individuals who can then spread the virus to others.
In its “Morbidity and Mortality Weekly Report,” the CDC on Friday revealed that 75 percent of patients in a cluster of 469 cases in Provincetown, Massachusetts, were vaccinated, a sobering statistic for Americans who only weeks ago were optimistic that the pandemic’s end was in sight.
“New scientific data shows that Delta behaves differently than other variants,” CDC Director Rochelle Walensky said in a briefing last Wednesday. “On rare occasions, some vaccinated people may be contagious and spread the virus to others.”
Mark Poznansky, director of Massachusetts General Hospital’s Vaccine and Immunotherapy Center and an associate professor of medicine at Harvard Medical School, has seen up-close the situation Walensky discussed, including “breakthrough” cases of COVID-19 in vaccinated individuals.
Many of these patients shrug off initial symptoms, Poznansky said, attributing them to a cold or some other mild ailment. When the condition worsens, they get tested and ask for treatment advice, but the delay means that they might have been spreading the virus as they went about their lives. Poznansky, whose clinical practice at MGH is focused on immune-compromised patients who are potentially vulnerable even when vaccinated, said it’s important that vaccinated individuals get tested right away if they feel sick with COVID symptoms.
For vaccinated people who develop symptoms, “The stress should be on testing along with mask-wearing in public spaces and self-isolating where possible,” he said.
The Delta variant has spread rapidly across the country, with the CDC reporting last week that it has been detected in eight in 10 samples nationally. In Massachusetts, the recent increase in cases — still at a far lower level than in U.S. hotspots — has been virtually all Delta, according to Jacob Lemieux, an instructor in medicine at Harvard Medical School and an infectious disease expert at Mass General.