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delta is more contagious than the original COVID-19 virus and even more contagious than the other worrying variants. That’s why the CDC recently recommended masking in some situations, even if you are vaccinated – as many public health experts have been calling for since Delta spread.

So how contagious is it? ON recently leaked CDC document contains some new data to put it into perspective.

Delta (blue box) is far more contagious and perhaps a little more deadly than the original (pink box) COVID.  Delta is more contagious than a host of other diseases, including the common cold, Ebola, and flu.  It's less deadly than Ebola, of course.

Screenshot: CDC

The CDC slides show a rough estimate of the infection and death rate from Delta, in addition to this New York Times graphh from earlier in the pandemic.

Delta might be a little more deadly than the original COVID (SARS-CoV-2 is the official name of the COVID virus), but most importantly, it’s much more contagious. The cold and various flu viruses are all about as contagious as the original COVID, but Delta is far more so. Not as much as measles, a classic super spreader, but about as much as chickenpox.

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If you’re old enough to remember chickenpox outbreaks as a kid, that sucks. I got chickenpox just a few years before the chickenpox vaccine came out, and as soon as a kid in our neighborhood got it, our parents knew that there was a good chance everyone would get it sooner or later.

It is very unlikely that people who are vaccinated will get Delta or any variant of COVID.

Do vaccinated people spread Delta?

If you’ve heard that vaccinated people shed just as much virus as unvaccinated people, that’s true, but only in the context of people who actually get sick. It is very unlikely that people who are vaccinated will get Delta or any variant of COVID. On the rare occasions when they do, they have the same viral load as unvaccinated people who contracted the virus.

People who are vaccinated and have not contracted Delta do not spread the virus or excrete virus particles or spike proteins or anything else. The problem isn’t with the vaccine, just that the vaccine isn’t perfect.

“Delta variant breakthrough cases can be just as transferable as unvaccinated cases,” said the CDC presentation. Prior to Delta, breakthrough cases were thought to be potentially less communicable than cases in unvaccinated people who contracted COVID.

CDC slide: higher risk of illness, hospitalization and death in unvaccinated compared to vaccinated people

Screenshot: CDC

To be completely clear about what the vaccine does for us, the data from the CDC shows that the vaccines are working well. Currently, unvaccinated people have an eight times higher incidence of COVID than vaccinated people and a 25 times higher risk of dying from COVID.

In the CDC presentation it says: “[g]In view of the higher transferability and current vaccination protection, universal masking is essential to reduce the transmission of the Delta variant. ”The CDC recently chose a less drastic message in its announcement and recommends masks depending on your personal situation and the transmission rate in your county . However, it’s also important to note that the spread of Delta will slow down as more people are vaccinated and masks may not be required when cases are low enough.