Thread by @ASlavitt

COVID Update: 2 weeks ago we said we would know a lot more about Omicron in 2 weeks.

I’ve rounded up the best scientific opinions to share a consensus. 1/

The bottom line-up front: We should expect a significant wave of COVID this weekend: likely a Delta + Omicron wave. 2/

The consensus view of Omicron is that it is NOT innately more contagious, but that it IS spreading much faster. 3/

What is wrapped up in that enigma is that the R0, the reproductive rate that Omicron spreads in the wild is likely no greater than Delta.

Delta is a 6 or 7 R0 and Omicron may be a bit lower or only slightly higher. But…. 4/

The virus spreads based on not just the rate COVIS spreads in the wild but what portion of the people are succeptable to spread.

Delta spread is limited by the people who are vaccinated & who have prior infections. Omicron, for reasons I will lay out, has a more open field. 5/

As a result, the rate Delta actually spreads (Re) is about 1
& the rate Omicron spreads is closer to 2.5.

So it should feel like Omicron is growing about 2.5x as fast as Delta. Most of what we see is from the S African outbreak & more recently from the U.K. 6/

The reason Omicron is able to spread with little in its way stems from the fact that Omicron comes from a different lineage than Delta. Therefore prior infection from Delta does a poor job protecting against spread & infection if there is no vaccination. 7/

How do vaccines themselves perform?

Good and bad.

Limited data from Pfizer shows that with a 3rd dose, the vaccine will continue to do a very good job—particularly at preventing severe illness.

Even with that third dose/booster, it appears to have some fall off from Delta.8/

Without a booster, vaccines aren’t expected to do a great job preventing the virus from spreading, although still provide strong protection against severe illness. 9/

This is relieving news for people who have gotten or will get boosted.

For people who are vaccinated but not boosted there is real risk of breakthrough infection.

But anyone who has been vaccinated is far better off than those who haven’t. Prior infection isn’t a help. 10/

The other question we began wrestling with— and are still wrestling with— is whether the COVID that people get w Omicron is more or less severe. 11/

Depending who you ask, Omicron is either more, less, or equally severe.

Now that that’s cleared up, there is an interesting & important theory of the case. 12/

The perspective I find most compelling is that Omicron is not likely to be more or less severe than Delta but that we may be seeing the effects of memory B cell and T cell accumulated immunity. 13/

This would be similar to what’s happening as we look at how fast the virus spreads. What we’re seeing is clouded by the impact of prior infection, not the innate properties of the virus itself. 14/

If it turns out that Omicron is less lethal because more people have cellular protection that’s an overall good thing for the population— it means we are making progress towards making the virus less lethal. But…
15/

It would be even better if Omicron were less lethal than Delta innately. We still have many people— like those under 5– with no protection and those with compromised immune systems.
16/

So what happens when Omicron begins to grow in the US? What would an even more rapidly growing virus (250% faster than Delta) that is less lethal look like?

It can be damaging. Even a small percentage of a big number is a big number. 17/

If Omicron were the only challenge of the winter, it would be easier to manage. But Omicron will arrive when Delta is raging. And if Delta spreads as fast or faster than Omicron innately, then scientists tell me we are likely to get stuck with both. 18/

Both.

That means two viruses circulating, 2 types of immunity required to thwart infection. 2 cycles of spread.

We have had 2 strains of the flu before. 2 flu vaccines combined.

One solution. 19/

A third shot on top of 2 prior shots works well against Delta and appears to make a big difference with Omicron. 20/

Rapid tests. Therapeutics. Ventilation. n-95 masks.

All help on top of vaccines. 21/

And this is how the winter of 2021-2022 is different from last winter.

As bad a storm as comes, we have the tools to stay safe. If we use them. /end

And if you want to hear the podcast with @ScottGottliebMD on the topic on @inthebubblepod, listen here.

podcasts.apple.com/us/podcast/in-…

Tweet 3 should say “this winter” not “this weekend.”

Why was I thinking about the weekend on a Wednesday? That never happens.

Errant tweet. Should say “winter” not “weekend.”

Now back to the thread.