SARAH MCCAMMON, HOST:
The war against the coronavirus has changed. That's according to an internal document from the CDC that reveals just how dangerous the delta variant is. The document was first reported and published by The Washington Post. And it comes after President Biden announced new vaccination rules for federal employees and contractors.
NPR health correspondent, Rob Stein, is here to give us more details. Good morning, Rob.
ROB STEIN, BYLINE: Good morning, Sarah.
MCCAMMON: What is this new analysis from the CDC, and what does it say exactly?
STEIN: Well, that sentence you mentioned kind of sums it up. The war has changed. And that's basically the conclusion of this 25-page document, which summarizes what CDC experts determined about some of the most crucial questions about the delta variant. How fast does it grow inside people's bodies? Why does it spread so much more easily from one person to another? How sick does it make people? And all those scores - delta clearly poses a huge threat.
MCCAMMON: Now, we've known for a while that the delta variant is the most transmissible variant so far. So what's new here?
STEIN: One of the most dramatic parts of this document says the delta variant could be as contagious as chickenpox, which is one of the most transmissible viruses out there, and could be more transmissible than the common cold, Ebola and smallpox. The document also includes evidence for why that is. Studies from India, for example, show that people infected with delta are carrying around far more virus than earlier strains. They have higher viral loads, perhaps 10 times higher.
Also, there was an investigation of a superspreader event that occurred July 4 weekend on Cape Cod in Massachusetts. And that produced more really important revelations. Investigators found that vaccinated people had as much virus inside them as unvaccinated people, which explains why the virus spread to so many people, even if they were vaccinated. So it turns out vaccinated people still can get infected through so-called breakthrough infections and spread the delta variant just as easily as unvaccinated people. That helps explain why the CDC did that big about-face on masks this week and told vaccinated people to start wearing masks again, even - when they're in places where there's a lot of virus around.
MCCAMMON: Some concerning details there - Rob, what else struck you in this new document?
STEIN: Yeah. So, you know, another worrying conclusion is that delta appears to make people sicker than the earlier strains. There's been a big debate about that. There was this one study out of Scotland that suggested that might be the case. This document cites additional evidence from Canada and Singapore that people who catch the delta strain are more likely to get really sick.
In Canada, patients infected by delta look like they were more than twice as likely to end up in a hospital, almost four times as likely to end up in intensive care and almost 2 1/2 times more likely to die. In Singapore, patients were nearly twice as likely to develop pneumonia and almost five times as likely to need oxygen and end up in intensive care or die. So that's obviously all pretty disturbing.
MCCAMMON: Yeah. Rob, people are so weary of this pandemic. This is discouraging news. Is there any good news in here?
STEIN: Yeah, yeah. This analysis also concludes that while the vaccines may not completely protect people from catching or spreading the virus, they are still incredibly powerful at reducing the risk of getting really sick and dying. This analysis concludes that the risk of an infection is reduced by threefold and the risk of severe disease or death is cut by at least tenfold. So this document recommends what we're starting to hear and see already - you know, things like vaccine mandates for health care workers and more masking.
MCCAMMON: NPR health correspondent, Rob Stein, thank you.
STEIN: You bet, Sarah.
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