Internal CDC Report Underscores Delta Dangers, COVID-19 Communication Woes

This story was updated August 3, 2021 to reflect added guidance about masking.

A newly released internal document from the CDC illustrates just how dangerous the COVID-19 delta variant is, as it now appears fully vaccinated individuals are at a higher than previously thought risk of developing breakthrough infections and can spread the virus more easily to others.

Increased rates of breakthrough cases not only lead to more illness, but also could undermine the public’s perception that the vaccines are effective. In the report, first obtained by The Washington Post Thursday night, the CDC stressed the importance of updated communication about the virus; while describing the breakthrough infections as “rare,” the agency also stressed that vaccination results in less-severe illness and fewer hospitalizations among the small percentage of people who do get a breakthrough infection.

The data come as the CDC updated its masking recommendations for fully vaccinated individuals last week, now urging all those in areas with substantial transmission to mask up indoors, regardless of vaccination status.

However, the newly released report reads “given higher transmissibility and current coverage, universal masking is essential to reduce transmission of the delta variant." It is unclear whether a universal masking recommendation will be announced.

The documents also make clear the agency’s struggle to effectively communicate the risks of delta while encouraging more individuals to get vaccinated.

Currently, it is estimated there are 35,000 symptomatic cases of COVID-19 per week among the 162 million vaccinated Americans. The preliminary data also show an increased percentage of vaccinated persons among those hospitalized with COVID-19 listed in the Hospitalization Surveillance Network.

But figures do show that among those who are fully vaccinated, these individuals still have an 8-fold reduction in disease incidence, a 25-fold reduction in hospital incidence, and a 25-fold reduction in death incidence. Risk of severe disease is still dependent on an individual’s age and underlying conditions.

When it comes to delta’s transmissibility “breakthrough cases reported to national passive surveillance have lower cycle threshold (Ct) values by 3 cycles (~10-fold increase in viral load) for Delta (Ct=18, n=19) compared with Alpha (Ct=21, n=207) and other lineages (Ct=21, n=251).”

In addition, a single study conducted during an outbreak in Massachusetts in July 2021 showed similar Ct values among vaccinated and unvaccinated individuals, meaning each group could have been equally as likely to transmit the virus.

According to the CDC's latest Morbidity and Mortality Weekly Report (MMWR), 74% of those infected during this outbreak were fully vaccinated against COVID-19, while the delta variant was identified in 90% of specimens tested.

Of the breakthrough infections, 79% were symptomatic and among the 5 patients hospitalized, 4 were fully vaccinated. No deaths were reported.

"Findings from this investigation suggest that even jurisdictions without substantial or high COVID-19 transmission might consider expanding prevention strategies, including masking in indoor public settings regardless of vaccination status, given the potential risk of infection during attendance at large public gatherings that include travelers from many areas with differing levels of transmission," the MMWR reads.

However, authors noted as population-level vaccination increases, vaccinated individuals will account for more COVID-19 cases reported.

"This outbreak investigation is one of many CDC has been involved in across the country and data from those investigations will be rapidly shared with the public when available," CDC director Rochelle Walensky, MD, MPH said in a statement.

Previously published research out of Canada, Singapore and Scotland also underscores the more dangerous nature of delta, showing the strain leads to higher odds of hospitalization, oxygen requirement, intensive care unit (ICU) admission, and death.

Given different states’ spotty vaccination rates, non-pharmaceutical interventions are key to combatting the delta variant, the report states.

Among recommendations made are improved communication by the CDC that the war against COVID-19 has changed, due to the more dangerous nature of this variant. The report also recommends universal vaccination among health care providers, in addition to universal masking and consideration of other community mitigation strategies.