Internal Centers for Disease Control and Prevention documents support the high transmission rate of the Delta variant and put the risk in easier to understand terms.
In addition, the agency released a new study that shows that breakthrough infections in the vaccinated make people about as contagious as those who are unvaccinated. The new report, published July 30 in Morbidity and Mortality Weekly Report (MMWR), also reveals that the Delta variant likely causes more severe COVID-19 illness.
Given these recent findings, the internal CDC slide show advises that the agency should “acknowledge the war has changed.”
A ‘pivotal discovery’
CDC Director Rochelle Walensky, MD, MPH, said in a statement that the MMWR report demonstrates “that [D]elta infection resulted in similarly high SARS-CoV-2 viral loads in vaccinated and unvaccinated people.
“High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with [D]elta can transmit the virus,” she added. “This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation.”
The investigators analyzed 469 COVID-19 cases reported in Massachusetts residents July 3 through 17, 2021. The infections were associated with an outbreak following multiple events and large gatherings in Provincetown in that state’s easternmost Barnstable County, also known as Cape Cod.
Notably, 346 infections, or 74%, of the cases occurred in fully vaccinated individuals. This group had a median age of 42, and 87% were male. Also, 79% of the breakthrough infections were symptomatic.
Researchers also identified the Delta variant in 90% of 133 specimens collected for analysis. Furthermore, viral loads were about the same between samples taken from people who were fully vaccinated and those who were not.
Four of the five people hospitalized were fully vaccinated. No deaths were reported.
The publication of these results was highly anticipated following the CDC’s updated mask recommendations on July 27.
Outside the scope of the MMWR report is the total number of cases associated with the outbreak, including visitors from outside Massachusetts, which now approach 900 infections, NBC Boston reported.
‘Very sobering’ data
“The new information from the CDC around the [D]elta variant is very sobering,” David Hirschwerk, MD, infectious disease specialist at Northwell Health in New Hyde Park, N.Y., said in an interview.
“The CDC is trying to convey and present this uncertain situation clearly to the public based on new, accumulated data,” he said. For example, given the evidence for higher contagiousness of the Delta variant, Dr. Hirschwerk added, “there will be situations where vaccinated people get infected, because the amount of the virus overwhelms the immune protection.
“What is new that is concerning is that people who are vaccinated still have the potential to transmit the virus to the same degree,” he said.
The MMWR study “helps us better understand the question related to whether or not a person who has completed a COVID-19 series can spread the infection,” agreed Michelle Barron, MD, a professor in the division of infectious disease at the University of Colorado, Aurora.
“The message is that, because the [D]elta variant is much more contagious than the original strain, unvaccinated persons need to get vaccinated because it is nearly impossible to avoid the virus indefinitely,” Michael Lin, MD, MPH, infectious diseases specialist and epidemiologist at Rush University Medical Center, Chicago, said when asked to comment.
The new data highlight “that vaccinated persons, if they become sick, should still seek COVID-19 testing and should still isolate, as they are likely contagious,” Dr. Lin added.