A new study shows the Delta Covid-19 variant produced similar amounts of virus in vaccinated and unvaccinated people if they get infected.
This illustrates the key motive behind federal guidance that is now recommending most fully vaccinated Americans wear masks indoors.
Experts say that vaccination makes it less likely that you’ll catch Covid-19 in the first place –but for those who do, this data suggests they could have a similar tendency to spread it as unvaccinated folks.
Rochelle Walensky, director of CDC, said in a statement today.
“High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with Delta can transmit the virus.”
The study, published by CDC Friday, describes 469 Massachusetts residents who were infected in a July outbreak in Barnstable County, which includes the gay destination hotspot, Provincetown. The town manager of Provincetown, Alex Morse, said Friday that the town appeared to be taking a favorable turn, with an indoor mask mandate in place,
“We think we’re heading in the right direction, but obviously concerned about what’s happened here in the last few weeks.”
According to CNN,
About 74% –or 346 cases– had been fully vaccinated. Of those cases, 79% reported symptoms. Genetically sequenced cases revealed the Delta variant as the main culprit.
The researchers found evidence that viral loads were similar among 127 fully vaccinated people and 84 others who were unvaccinated, partially vaccinated or whose vaccination status was unknown. Viral load is a proxy for how likely someone might be to transmit the virus to others. On Tuesday, Walensky previewed these findings while unveiling guidance that people in areas with “high” or “substantial” Covid-19 transmission should resume wearing masks indoors. Over 75% of the US population live in these areas. The finding that the Delta variant resulted in similar viral loads “was a pivotal discovery leading to CDC’s updated mask recommendation.”
Walensky said Friday,
“The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones.”
Prior to Delta, vaccination was known to impact factors that likely influence transmission. Not only did vaccinated people tend to have lower viral loads, but they also had milder symptoms and were sick for less time.But research has shown that Delta spreads more aggressively.
On Thursday, a CDC internal document said the Delta variant was roughly as transmissible as as chickenpox, whereas 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, early in the outbreak. But now, with Delta, that number could be five to nine.
Walensky said late yesterday,
“It’s one of the most transmissible viruses we know about. Measles, chickenpox, this– they’re all up there.”
Even with Delta, Covid-19 vaccines still reduce the spread of the virus. Moreover, vaccinated people are far less likely to end up in the hospital.
New @CDCMMWR finds Delta variant causes vaccine breakthrough infections. Jurisdictions might consider expanded prevention strategies, including masking in indoor public areas, particularly for large public gatherings that include travelers from many areas. https://t.co/Q8d9kmQ4Mj pic.twitter.com/aTR6bKTwER— CDC (@CDCgov) July 30, 2021