CDC: 74% of COVID-19 Cases in Cluster Happened Among Vaccinated


The CDC data seem to show just how vulnerable even vaccinated people are to the Delta variant.

First thing’s first: No one died. Unfortunately, that’s not the main takeaway in data unveiled today by the Centers for Disease Control and Prevention (CDC) saying that 74% of a COVID-19 cluster in a town in Cape Code (identified as Provincetown in published reports) occurred among people who had been vaccinated. The data were included in an early release study in the CDC’s Morbidity and Mortality Weekly Report (MMWR).

The study states that “469 COVID-19 cases were identified among Massachusetts residents who had traveled to the town during July 3–17; 346 (74%) occurred in fully vaccinated persons. Testing identified the Delta variant in 90% of specimens from 133 patients. Cycle threshold values were similar among specimens from patients who were fully vaccinated and those who were not.”

Kevin Kavanagh, MD, a member of Infection Control Today®’s Editorial Advisory Board urged early this week in a Q&A with ICT® that, as the headline to the article put it: “Everybody Needs to be Vaccinated and Wear a Mask.”

The MMWR study isn‘t that blunt but it does state that “jurisdictions might consider expanded prevention strategies, including universal masking in indoor public settings, particularly for large public gatherings that include travelers from many areas with differing levels of SARS-CoV-2 transmission.”

CDC Director Rochelle Walensky, MD, said in a statement that “rapid receipt and review of unpublished data” from the MMWR study made CDC officials change masking recommendations earlier this week. The CDC said that vaccinated individuals should begin wearing masks again when indoors in public settings in parts of the US with substantial to high transmission.

Massachusetts is one of the most vaccinated states, according to the CDC. The problem seems to stem from the fact that even in areas where most of the population has been vaccinated, people from outside that area can come in carrying the Delta variant.

The MMWR study states that “during July 3–17, 2021, multiple summer events and large public gatherings were held in a town in Barnstable County, Massachusetts, that attracted thousands of tourists from across the United States. Beginning July 10, the Massachusetts Department of Public Health (MA DPH) received reports of an increase in COVID-19 cases among persons who reside in or recently visited Barnstable County, including in fully vaccinated persons.”

About the MMWR study, Kavanagh said that “this outbreak makes the Israeli data which we reported on Wednesday look overly optimistic. In the Cape Cod outbreak, the vaccine appears to have had little efficacy in the prevention of infections or symptomatic disease. The data that we have today indicates the vaccines are highly effective in preventing hospitalization, severe disease and death. But it needs to be remembered that even those with mild infections can develop long COVID. A small study out of Israel which studied health care workers who had a vaccine breakthrough infection found 19% had symptoms greater than 6 weeks.”

Five people were hospitalized, and 4 of them had been fully vaccinated.

“Among persons with breakthrough infection, 274 (79%) reported signs or symptoms, with the most common being cough, headache, sore throat, myalgia, and fever,” the study states. “Among fully vaccinated symptomatic persons, the median interval from completion of ≥14 days after the final vaccine dose to symptom onset was 86 days (range = 6–178 days).”

Kavanagh pointed out that “the Delta variant is much more infectious, producing 1000 times more virions than the wild type of virus. And the viral load of individuals with breakthrough infections was the same as those who are not vaccinated. This outbreak occurred in a highly vaccinated area. We all need, regardless of where you live, you need to wear medical grade masks (preferably N95s) and become vaccinated.”

Related Videos
Anne Meneghetti, MD, speaking with Infection Control Today
Vaccine conspiracy theory vector illustration word cloud  (Adobe Stock 460719898 by Colored Lights)
Infection Control Today's topic of the month: Mental Health
Infection Control Today Topic of the Month: Mental Health
NFID Medical Director, Robert H. Hopkins, Jr., MD  (Photo courtesy by Evoke Kyne)
An eye instrument holding an intraocular lens for cataract surgery. How to clean and sterilize it appropriately?   (Adobe Stock 417326809By Mohammed)
Paper with words antimicrobial resistance (AMR) and glasses.   (Adobe Stock 126570978 by Vitalii Vodolazskyi)
 MIS-C (Adobe Stock 350657530 by Bernard Chantal)
Medical investigators going over data. (AdobeStock 589197902 by Wasan)
Related Content