CDC shares ‘crucial finding’ on groundbreaking Covid-19 infections that led to new mask guidelines

Researchers found evidence that viral loads were similar in 127 people who were fully vaccinated and 84 others who were unvaccinated, partially vaccinated, or whose vaccination status was unknown. Viral load is an indicator of how likely a person can transmit the virus to others.

On Tuesday, Walensky presented the results while unveiling guidelines that people living in areas with “high” or “substantial” transmission of Covid-19 should resume wearing masks indoors. Over 75% of the American population lives in these regions.

The discovery that the Delta variant resulted in similar viral loads “was a crucial finding leading to the CDC’s updated mask recommendation,” Walensky said Friday.

“The masking recommendation has been updated to ensure that the vaccinated public will not unknowingly transmit the virus to others, including their unvaccinated or immunocompromised loved ones.”

Questions remain

Prior to Delta, vaccination was known to have an impact on factors likely to influence transmission. Not only did those vaccinated tend to have a lower viral load, they also had milder symptoms and were sick for a shorter period of time.

But research has shown that Delta spreads more aggressively. Earlier this month, for example, Chinese scientists described viral loads about 1,000 times higher with Delta than previous strains.

On Thursday, an internal CDC document said the Delta variant was about as transmissible as chickenpox, while an early strain was closer to the common cold. This means that under certain conditions an infected person may have transmitted to two or three people, on average, by the start of the epidemic. But now, with Delta, that number could be five to nine.

“It’s one of the most transmissible viruses we know of. Measles, chickenpox, that – they’re all up there,” Walensky told CNN Thursday night.

The CDC document also cited reports indicating that the variant could also cause more serious illness.

But even with similar viral loads, it is not a given that vaccinated people are necessarily as contagious as unvaccinated people.

“This is intriguing data, it’s important, but I’m not sure you’re so contagious if you’re vaccinated,” said Dr Monica Gandhi, infectious disease specialist at the University of California, San Francisco, who was not involved in the research.

Gandhi said there are several parts of the immune system – including antibodies and T cells – that raise important questions about the use of viral load, which is measured by PCR tests, as an indicator of contagiousness. ‘a person.

The new report says “microbiological studies are needed to confirm these results” of similar viral loads among breakthrough infections. He also notes that “asymptomatic breakthrough infections might be underrepresented” because they are less likely to be detected.

Earlier this week, Walensky said ongoing outbreak investigations would help learn more about what happens when these breakthrough infections occur.

“We are now continuing to monitor these groups to understand the impact of advanced transmission from these vaccinated people,” she said. “But again, I want to reiterate, we believe that the vast majority of transmission occurs among unvaccinated people and by unvaccinated people.”

All the more reason to get vaccinated

Even with Delta, the Covid-19 vaccines are still reducing the spread of the virus. In addition, people who have been vaccinated are much less likely to end up in the hospital.

The CDC’s internal document estimated that vaccines reduce the risk of serious illness or death by a factor of 10 or more, and that they reduce the risk of infection by three times.

“Getting the vaccine continues to prevent serious illness, hospitalizations and death – even with Delta,” Walensky said this week.

Of the Massachusetts residents in the latest study, none died and only five were hospitalized.

Of those five people, one was unvaccinated and had underlying health problems, and four were vaccinated. Among the vaccinated group, one had received the Pfizer vaccine and the other three had received Johnson & Johnson. Those vaccinated were between 20 and 70 years old, and two had underlying health problems.

Additional infections were identified among visitors from at least 22 other states who visited the region from July 3 to 17. Thousands of people gathered for the summer festivities and infected people reported going to “densely packed indoor and outdoor events at venues including bars, restaurants, guest houses and rental accommodation,” the study says. .

While these findings motivated the CDC to update its guidelines for areas with higher levels of viral transmission, the study notes that Barnstable County was not among those areas until the outbreak. Between July 3 and July 17, new daily cases increased from a 14-day average of 0 to 177 cases per 100,000 population.

The study suggests that “even jurisdictions without significant or elevated transmission of COVID-19 could consider expanding prevention strategies, including masking in indoor public places, regardless of vaccine status.”

“The measures we need to get this under control – they’re extreme. The measures you need are extreme,” Walensky told CNN Thursday night.

The study also notes that revolutionary infections are expected, especially as the segment of the vaccinated population increases. “As vaccine coverage at the population level increases, those vaccinated are likely to account for a greater proportion of COVID-19 cases,” the authors wrote.

CNN previously reported on the outbreak linked to Provincetown. In total, at least 882 cases have been linked to the cluster so far, of which around 60% have been residents of Massachusetts, according to local officials.

Provincetown City Manager Alex Morse told CNN on Friday that the city appeared to be taking a positive turn – with an indoor mask mandate in place and a declining test positivity rate.

“We think we’re headed in the right direction, but we’re obviously concerned about what has happened here over the past few weeks,” Morse told CNN’s John Berman.

A source familiar with the CDC’s decision to update its recommendations previously told CNN that in addition to the viral load results, the overall prevalence of Delta and lower-than-expected vaccine uptake played a key role. in the last iteration of the guide.