Thread by @DearPandemic

(1/15)
Q: What actually is #HerdImmunity anyway?

The #nerdygirls explain what it is and how it might be achieved in this thread

(2/15)
A: The term "herd immunity" refers to a situation where a lot of people in a population are not susceptible to a virus--either because they have already had it and are unlikely to get it again, or because they've been vaccinated.

(3/15) That is to say, their immune systems have been primed to respond to the virus, and they won't get infected with it when they are exposed again.
If a lot of people are immune, the virus has a hard time finding a host that it can infect, replicate, and spread to a new host.

(4/15) With herd immunity, even though *some* of the people in a population are susceptible to the disease, they're unlikely to be infected simply because they probably won't encounter the virus circulating in the population in the first place.

(5/15) Herd immunity is achieved when as many people as possible are vaccinated, which helps protect those who cannot or will not be vaccinated.

Herd immunity does not directly protect individual people from infection. It limits how fast a virus can spread through a population.

(6/15)
One reason why #COVID19 spread so rapidly around the world is because billions of people were susceptible.
Up until just a few months ago, *no one* had ever had it. That means everyone was susceptible and the virus had no trouble at all finding new hosts.

(7/15) What would it take to get to herd immunity for #COVIDー19 ? Many scientists think something like 70-80% of the population would need to have immunity to produce herd immunity.

(8/15) How do we get to herd immunity?

There are two routes: 1. vaccination and 2. natural herd immunity.

Both face major obstacles to becoming the magic bullet that stops the #pandemic right now. More on each below

(9/15)
1. A vaccine.
The safest path to herd immunity (and maybe the only way) is to develop #vaccines, so that we can become immune without ever having to be infected. A vaccine works by giving your #ImmuneSystem clues as to how to identify the virus before you encounter it.

(10/15)
But a vaccine is a long ways off--at least 18 months, and maybe much longer.

Even after a vaccine is approved, it will take years to cover enough people to really produce herd immunity. Staying home until a vaccine becomes available isn’t a realistic option.

(11/15)
2. “Natural” herd immunity.
Okay so a vaccine is too far off. What if we just let everyone get #Covid_19 ?
As epidemiologist Gideon Meyerowitz-Katz says, “...this is simply nonsense. Herd immunity without a vaccine is by definition not a preventative measure.”

(12/15)
If we just let everyone get the disease, then everyone is sick. That’s not stopping the spread of the disease--it’s encouraging it!
This let-it-burn approach to achieving herd immunity would require hundreds of millions of people to fall ill all at once.

(13/15)
If we guess conservatively at a 2% mortality rate, we’re talking about over 4 million deaths in the United States alone! YIKES.
Plus, we are still learning about the long-term health consequences of #COVID__19 infection for survivors.

(14/15)
Not only that, we don’t yet know if recovering from #COVID means you are immune to it in the future. In fact, rapid widespread infection could provide the virus just the opportunity it needs to mutate more rapidly--which could undermine herd immunity!

(15/15)
Read more here: sciencealert.com/why-herd-immun…
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