Data show vaccinated people had similar viral loads to unvaccinated people and were contagious

Following its recent Covid-19 guidelines update stating that fully vaccinated Americans should wear a mask in indoor public setting in areas where there is substantial and high transmission of Covid-19, the CDC released some of the data upon which those guidelines are based.

The new data, published in the CDC’s Morbidity and Mortality Weekly Report (MMWR), shows that infection with the Delta variant of SAR-CoV-2 results in similarly high viral loads in both unvaccinated and vaccinated people.

These results coincided with a recent study published in The New England Journal of Medicine, in which researchers found that even fully-vaccinated health care workers could transmit the SARS-CoV-2 virus to others.

The new report centered on an outbreak of SARS-CoV-2 infections—including Covid-19 vaccine breakthrough infections—that were associated with large public gatherings held in Barnstable County, Massachusetts. Researchers reported 469 Covid-19 cases in Massachusetts residents who had attended multiple large public events held in this town. Despite a high vaccination rate of 69% in eligible Massachusetts residents, a full 74% of these infections (n=346) occurred in fully vaccinated people.

“On July 3, [the Massachusetts Department of Public Health] had reported a 14-day average Covid-19 incidence of zero cases per 100,000 persons per day in residents of the town in Barnstable County; by July 17, the 14-day average incidence increased to 177 cases per 100,000 persons per day in residents of the town,” wrote researchers.

Most cases occurred in men (85%), and the median age of people infected was 40 years. Five patients were hospitalized, and no deaths have been reported as of July 27. One hospitalized patient was unvaccinated and had several comorbid conditions. Four fully vaccinated people were also hospitalized, two of whom also had comorbid conditions.

Breakthrough infection caused symptoms in 79% of patients, the most common of which were cough, headache, sore throat, myalgia, and fever.

According to researchers: “Real-time reverse transcription–polymerase chain reaction (RT-PCR) cycle threshold (Ct) values in specimens from 127 vaccinated persons with breakthrough cases were similar to those from 84 persons who were unvaccinated, not fully vaccinated, or whose vaccination status was unknown (median= 22.77 and 21.54, respectively).”

High viral loads increase the risk of transmission, even in the fully vaccinated.

“This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation. The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones,” wrote CDC Director Rochelle P. Walensky, MD, MPH, in response to these new MMWR findings. “This decision was made with the data and science available to CDC at the time, including a valuable public health partnership resulting in rapid receipt and review of unpublished data.”

Liz Meszaros, Deputy Managing Editor, BreakingMED™

Cat ID: 125

Topic ID: 79,125,730,933,125,190,31,520,926,192,561,927,150,151,928,925,934