Delta variant spreads as quickly as chickenpox even among vaccinated, leaked CDC data concludes

Each person infected with the Delta variant can end up spreading the virus to eight or nine others

US President Joe Biden delivers remarks on the efforts to get more Americans vaccinated and the spread of the Delta variant in East Room of the White House in Washington, DC, USA, 29 July 2021 (EPA)

The Delta variant of the coronavirus spreads as quickly as chickenpox, even among those who are vaccinated, and appears to cause more severe illness, according to a leaked document of the US’s Centers for Disease Control and Prevention (CDC).

Each person infected with the Delta variant can, on average, end up spreading the virus to eight or nine others, making it as transmissible as chickenpox, according to the document.

The CDC should, thus, “acknowledge the war has changed” while recommending vaccine mandates and universal mask requirements, said the document, which is in the form of a slide presentation.

Still unpublished research cited by the document also pointed out that people who are fully vaccinated against Covid-19 might spread the Delta variant at a rate similar to their unvaccinated counterparts.

The document, however, said vaccinated people are safer, with the risk of severe disease or death decreasing 10-fold and the risk of contracting infection reducing as much as three times.

“Vaccines prevent more than 90 per cent of severe disease, but may be less effective at preventing infection or transmission. Therefore, more breakthrough and more community spread despite vaccination,” it said.

Dr Rochelle Walensky, the CDC director, confirmed the authenticity of the document that was first accessed by The Washington Post.

“I think people need to understand that we’re not crying wolf here. This is serious. It’s one of the most transmissible viruses we know about. Measles, chickenpox, this – they’re all up there,” she told CNN News.

Dr Walensky emphasised that students, staff and visitors in schools should wear masks at all times.

"The measures we need to get this under control – they’re extreme. The measures you need are extreme," she said.

On Tuesday, the CDC issued a recommendation that said vaccinated people must wear masks indoors in parts of the US where the delta variant is fuelling infection surges.

Over the last three weeks, the US has recorded close to a million cases.