Thread by @Bob_Wachter

Some folks are a bit confused about why things are likely to be much safer in a month than now – not why virus will peak & fall (we don’t entirely know) but why the risk to individuals will plummet – & with that, why activities that are unsafe now will be much safer then.(1/20🧵)

There are about a dozen factors that go into a risk assessment, and only one of them will fundamentally change: the probability that a person near me is infectious.
Let’s go through the other factors to isolate the one that makes virtually all the difference.(2/20)

Will the virus I'm exposed to next month be the same?

Almost certainly. Omicron's now the dominant (>95%) virus in the U.S. (Fig) and it’s a near-certainty that it will be that way next month.
Given its relative "mildness," I hope that's true in 6 months; time will tell.(3/20)

Will the virus have different properties in a month?

Almost certainly not. The current characteristics of Omicron – its high degree of infectiousness, moderate immune escape, and relative “mildness” – will continue to be its M.O., despite small mutations. (4/20)

Will my immunity to Omicron change in a month?

There are 4 things that can change:
1)If you get a (or another) vax, you’ll be more immune. Do it if eligible
2)If you get Omi between now & then, you'll be more immune
3)If you get an illness or begin a med that lowers...(5/20)

...your immunity, you’ll be less immune
4)If nothing happens, your immunity to Omicron won’t change (maybe a little time-based decay)
(Note: I find the evidence that “immune-enhancing” vitamins & health foods make a difference pretty unpersuasive. Cue the Tweetstorm!) (6/20)

Will the chances of me catching Omicron from a given encounter (ie, indoor gathering) change?

Not really, unless the environment changes (restaurant has installed better filters or ventilation). If you’ve lowered your personal protection (today you’d use a mask for a... (7/20)

... given encounter and next month you go mask-less or downgrade your mask from, say, N95 to surgical), this will raise the risk. (Importantly: that's if no other variable changes, but one will... read on.) (8/20)

So what gives? The virus is the same, your immunity is the same, the chances of getting infected from a given encounter much the same.
Yet I predict that I – and most of us – who are trying our best to dodge Omicron now will be more “open” next month. Does that make sense?(9/20)

Yes! It's all about community prevalence – basically the chances that the person next to you at the restaurant, the movie, or the store is infectious w/ Covid. It they're not, your encounter is 100% safe. If they are, your encounter is as risky as it is today. (10/20)

Today, near the Omicron peak, the odds an asymptomatic person has Covid is ~10% in most of U.S. At 10% prevalence, when you enter a room w/ 20 people, there’s an 88% chance that one of them has Covid. Do that enough times without masks and you’re going to get infected. (11/20)

In a month – if cases fall to prior non-surge #'s – the prevalence among asymptomatic people may be more like 0.2% – even in less vaxxed regions, which'll have more people whose immunity came from infection. (They should still get vaxxed for better & longer protection.) (12/20)

0.2% means that the odds of an asymptomatic person having Covid=1-in-500. That room of 20 people: now a 4% chance (1-in-25) that someone's infected. Not zero – you'll still want to be careful if you’re at very high risk. But for most, % is low enough to feel pretty safe. (13/20)

And here's where some other variables kick in. The low probability of being exposed to Covid should be multiplied by the probability that you’ll have a really bad case if you DO catch it. That chance has gone down with Omicron’s relative “mildness,”… (14/20)

… particularly if you’re vaccinated.
And with a low community prevalence, if you do get sick, hospitals won’t be overwhelmed and you’ll be able to get the care you need. That also makes an infection less risky. (15/20)

And tests will be more abundant, so you’ll be able to get diagnosed more quickly. And if you do get Covid & you’re at high risk, you’ll have an easier time getting a med (preferably the Pfizer pill, Paxlovid), which will markedly lower your chance of getting very sick. (16/20)

Yes, the specter of Long Covid (for some, mild; others disabling) continues – maybe a ~5% chance in a vaxxed person. Some will look at those odds as being concerning enough that they'll continue to act very cautiously. I probably won’t, but it’s an understandable choice. (17/20)

And others who have lots of contact w/ very vulnerable people – unvaxxed who didn’t get Omicron, for example, or immunosuppressed – may also make different choices. That’s entirely reasonable. This is very personal stuff and these individual decisions should be respected. (18/20)

As for me, this is why the community prevalence (cases, test pos %) will dominate my decisions. If they don’t plummet, I’ll keep my guard up until they do. And while I’m reasonably confident about the Spring, my confidence level falls as we move to later in the year. (19/20)

I hope this helps as you think about your own risk calculations... particularly why it's perfectly rational to be acting very cautiously now, while planning (& hoping) to make some different – & equally rational – decisions re: masking, dining, travel, etc. in 1-2 months.(20/end)