“A Covid-19 outbreak on Cape Cod helped prompt the Centers for Disease Control and Prevention to urge some Americans to start wearing masks again, the agency said, because it demonstrated that vaccinated people infected with the Delta variant might be as contagious as those who are unvaccinated.
The CDC said in a report on Friday that 127 vaccinated people infected with the Delta variant during the outbreak appeared to carry as much virus as 84 unvaccinated or partially vaccinated people who became infected. The report referred to an outbreak in Barnstable County, Mass. Local officials there have said that at least 430 confirmed Covid-19 cases have been linked to one cluster following festivities over the July 4 weekend in Provincetown, on the tip of Cape Cod.
"High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with Delta can transmit the virus," CDC Director Rochelle Walensky said Friday. "This finding is concerning and was a pivotal discovery leading to CDC's updated mask recommendation."
An internal CDC slide presentation earlier this week described the Delta variant as infectious as chickenpox, which used to sicken some four million Americans a year before a vaccine became available in the mid-1990s. The Delta variant is more transmissible than the common cold, seasonal flu and smallpox, but less contagious than measles, according to the presentation, which was first reported in the Washington Post.
"The war has changed," the presentation said.
The presentation said the agency must improve its communications around breakthrough infections, or people being infected after receiving the vaccine. It also underscored the importance of vaccines in fighting Covid-19. Vaccination reduces the risk of severe disease and death from Covid-19 by at least 10-fold and reduces the risk of infection by threefold, the presentation said.
It isn't clear just how common breakthrough infections are and how much they contribute to the virus's spread. The CDC stopped tracking all reported breakthrough cases that don't lead to hospitalization or death in April. Dr. Walensky said Tuesday that the agency is studying breakthrough infections at sites across the country.
Epidemiologists and physicians say the current wave of infections and hospitalizations in the U.S. is largely being driven by transmission among unvaccinated people, and areas with lower vaccine coverage have so far been hit harder.
The vaccines authorized for use in the U.S. were designed to prevent symptomatic disease from Covid-19. Data suggest that they continue to largely protect people from the worst consequences of Covid-19. The CDC has said virtually all people hospitalized with Covid-19 in recent weeks have been unvaccinated.
How well the vaccines protect against infection and transmission has been less clear. Data collected following their authorization suggested that vaccinated individuals who did get infected carried less virus and were less likely to transmit the virus, but those samples were taken before the Delta variant arrived in the U.S.
Dr. Walensky said Tuesday that everyone, including vaccinated people, should wear masks in indoor public spaces in areas where the Delta variant is spreading rapidly, and that everyone in K-12 schools should wear a mask this fall. Earlier in July, the CDC said only unvaccinated people in schools would need to wear masks.” [1]
Unvaccinated or immunocompromised people should again wear the mask interacting with vaccinated family members who can transmit the virus without symptoms.
1. Cape Cod Outbreak Prompted New CDC Guidelines --- Report shows that vaccinated people may spread the Delta variant of Covid-19. Abbott, Brianna. Wall Street Journal, Eastern edition; New York, N.Y. [New York, N.Y]31 July 2021: A.1.
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