An expert explains why vaccines — and masks — are so important, and why delta is different and more dangerous.
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3. Much more infectious. This much higher load plus the ultra “stickiness” of the delta strains for adhering to human cells makes it remarkably more infectious than previous strains. You may have heard of R0 (Pronounced R naught) which is, in a nutshell, the number of people to which an infected person would be expected to transmit the virus. Early versions of the virus had a 2 to 2.5 R0 value. So one infected person would infect two or so people on average. Delta has an R0 of about eight! In the infectious disease world, that’s almost unheard of. Chickenpox and measles are about all we have ever seen that spread that efficiently from human to human. This changes the story line completely from earlier in the pandemic and makes this surge, in many ways, like a completely different pandemic event.
4. Five days. There is another recent publication out of Singapore with data that confirms something we suspected. I will explain more about the “why” on this below when I talk about vaccines, but the gist is this: The viral loads in the
throats of vaccinated persons who become infected with delta rises at identical rates as in unvaccinated persons, but only for the first few days. After five days or so, the viral loads in the vaccinated person start to quickly drop whereas those in the unvaccinated person persist. This key set of observations is important for several reasons relating to vaccinated persons serving as vectors for spread (see below).