The CDC now urges public indoor masking after a worrisome study on the Delta variant — undermining the vaccine effort.
We finally know what drove the CDC to revise its guidance days ago without explanation to recommend that fully vaccinated individuals wear masks in public indoor settings in areas of the country with high or substantial COVID-19 transmission. The Washington Post released a July 29 CDC slide presentation, and the CDC confirmed that one of the unpublished studies cited was pivotal in its decision.
The slides largely just confirm what was already known: The Delta variant is more contagious than earlier variants.
Two of the slides suggest people with breakthrough Delta infections can spread the virus to others, leading to the claim vaccinated people must wear masks. In fact, a nonpeer-reviewed, preprint study claimed that breakthrough Delta infections are more transmissible than breakthrough infections from other variants. It examined breakthrough infections in 100 Indian health-care workers and found higher viral loads in Delta infections compared with non-Delta infections, leading to increased transmission. But — some say crucially — this small study used an Indian version of the AstraZeneca vaccine which is not used in the US. It may have limited relevance to the mRNA vaccines used here.
The slides also reported unpublished data, now updated by the CDC, that convinced the agency to take action: 74 percent of the 469 cases in an outbreak in Barnstable County, Mass., following the July 4 weekend were in vaccinated people and most showed symptoms. Among cases who had genomic sequencing and viral load determinations, there was no difference in Delta viral load between 127 vaccinated cases and 84 unvaccinated cases. This suggests Delta breakthrough cases pose as high a transmission risk as regular Delta cases, which is higher than other variants.
But does this one study really warrant a large change in policy?
It is difficult to assess unpublished data. Only time and published studies will tell if this report is accurate.
But it is odd that there are no similar findings in studies from areas like India and the UK, where the Delta variant has been prevalent for months. An outbreak where three-quarters of cases were breakthrough cases among those who had been vaccinated and most were symptomatic is unprecedented. It strongly suggests detection bias — only cases that became ill were testing leading to an undercount of asymptomatic cases. In addition, the CDC acknowledged that the outbreak occurred after public events marketed to adult men and that the study lacked information about underlying health conditions, including immunocompromising conditions, that might have made study participants particularly susceptible to infection and higher viral titers.
Unfortunately, the report did not describe the severity of symptoms or connect them to the amount of virus. Yet it is hugely important to note that few patients were hospitalized and none died. It may be that, as with earlier variants, most breakthrough cases are only mildly symptomatic and that asymptomatic and mildly symptomatic Delta breakthrough cases have low viral loads and pose little threat to others. It would have been helpful to answer this question before acting.
Read the full article at the New York Post.