A latest document from the US Centers for Disease Control (CDC) and Prevention has just driven home the crucial point that the Delta variant of the coronavirus appears to cause more severe illness than earlier variants and spreads as easily as chickenpox. Even more alarming is the finding that vaccinated people can spread the virus as easily as those who are unvaccinated. Vaccinated people infected with Delta have measurable viral loads similar to those who are unvaccinated and infected with the variant. CDC scientists were so alarmed by the new research that the agency last week significantly changed guidance for vaccinated people even before making new data public.
The data and studies cited in the document played a key role in revamped recommendations that call for everyone in the US — vaccinated or not — to wear masks indoors in public settings in certain circumstances. There is a higher risk among older age groups for hospitalisation and death relative to younger people, regardless of vaccination status. The document outlines “communication challenges” fuelled by cases in vaccinated people, including concerns from local health departments about whether coronavirus vaccines remain effective and a “public convinced vaccines no longer work/booster doses needed.”
It was on May 13 that people in the US were told they no longer needed to wear masks indoors or outdoors if they had been vaccinated. The new guidance reflects a strategic retreat in the face of the Delta variant. Even people who are vaccinated should wear masks indoors in communities with substantial viral spread or when in the presence of people who are particularly vulnerable to infection and illness, the CDC said. The CDC’s revised mask guidance stops short of what the internal document calls for. “Given higher transmissibility and current vaccine coverage, universal masking is essential to reduce transmission of the Delta variant,” it states.
The document makes clear that vaccination provides substantial protection against the virus. But it also states that the CDC must “improve communications around individual risk among [the] vaccinated” because that risk depends on a host of factors, including age and whether someone has a compromised immune system. The document includes CDC data from studies showing that the vaccines are not as effective in immunocompromised patients and nursing home residents, raising the possibility that some at-risk individuals will need an additional vaccine dose.
It is understood that the data used to prepare the CDC document came from a July 4 outbreak in Provincetown, Massachusetts. Genetic analysis of the outbreak showed that people who were vaccinated were transmitting the virus to other vaccinated people. If the war has changed, as the CDC states, so has the calculus of success and failure. The extreme contagiousness of Delta makes herd immunity a more challenging target, infectious-disease experts said. As Kathleen Neuzil, a vaccine expert at the University of Maryland School of Medicine, said, getting more people vaccinated remains the priority, but the public may also have to change its relationship to a virus almost certain to be with humanity for the foreseeable future.
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