The race for vaccines to triumph over variants appeared to suffer a blow as the US Centers for Disease Control released an analysis that found fully immunized people with so-called breakthrough infections of the Delta variant can spread the disease as easily as unvaccinated people.
While the jabs remain effective against severe disease and death, the US government agency said in a leaked internal CDC document “the war has changed” as a result of Delta.
An analysis of a superspreading event in the northeastern state of Massachusetts found three-quarters of the people sickened were vaccinated, according to a report the CDC published Friday.
The outbreak related to July 4 festivities, with the latest number of people infected swelling to 900, according to local reports. The findings were used to justify a return to masks for vaccinated people in high-risk areas.
“As a vaccinated person, if you have one of these breakthrough infections, you may have mild symptoms, you may have no symptoms, but based on what we’re seeing here you could be contagious to other people,” Celine Gounder, an infectious diseases physician and professor at New York University, told AFP.
As transmissible as chickenpox
According to the leaked CDC document, a review of findings from other countries showed that while the original SARS-CoV-2 was as contagious as the common cold, each person with Delta infects on average eight others, making it as transmissible as chickenpox but still less than measles.
Reports from Canada, Scotland, and Singapore suggest Delta infections may also be more severe, resulting in more hospitalizations.
China raced Saturday to contain its worst coronavirus outbreak in months, as health officials blamed the Delta variant for a surge in infections spanning 14 provinces.
“The main strain circulating at present is the Delta variant... which poses an even greater challenge to virus prevention and control work,” Mi Feng, spokesman for the National Health Commission (NHC), said at a press briefing.