David Dowdy Profile picture
Jul 21, 2021 9 tweets 4 min read Read on X
If you're in the US right now, how worried should you be about the recent uptick in COVID cases?

A plain-language thread below.

Long story short - the 4th wave is here, and it's time to start acting now before things get worse. But without hitting the panic button.
1. Let's start with the bad news.

Cases are doubling about every 9 days right now - nationwide. This is eerily similar to the rate of increase when each of the previous 3 waves hit. And no state is being spared.

In terms of case counts, the 4th wave is happening. Now.
2. COVID deaths are likely to follow.

We generally see a 3-week delay between when cases go up and when deaths increase.

Since cases have only been increasing for 3 weeks now, we haven't seen an increase in deaths - but we will soon.
3. And even though nearly half the population is fully vaccinated, things can still get a lot worse.

In the UK, for example, vaccination levels are very similar to those in the US. And the UK has seen a huge surge - cases are now back where they were in January.
4. Also - like it or not, we're all in this together.

What began as an outbreak in states like AK, MO, NV has now spread across the country.

Even if vaccination levels are high where you live - if rates are going up in other places, the wave will eventually hit your area too.
5. But there's also room for hope.

First, the one population in which COVID cases are staying stable is people 65+ years old (because their vaccination levels are much higher).

COVID can kill (or cause long-term effects) at any age. But vaccines are protecting older age groups.
6. Thanks to vaccines, deaths will rise more slowly than cases this time.

In the UK (below), cases have multiplied ~20x, but deaths so far only ~5x.

In the US, this would be ~1300 deaths/day.

That's 25 COVID deaths for every homicide. But still only 40% of what we saw in Jan.
7. Most importantly, it's not too late to act.

The UK and Portugal were the first 2 countries in Europe hit hard by this wave. Portugal adopted a more proactive approach.

Case rates in Portugal are now 50% those in UK. Plus, deaths are stable, vs doubling every 2 wks in the UK.
To summarize, the 4th wave is here.

Cases are doubling every 9 days, deaths will rise soon, and things can get a lot worse before they get better.

But vaccines will make this wave less severe - and if we take action now, we can prevent ~1000 deaths per day in the coming weeks.

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More from @davidwdowdy

Jul 8, 2022
Over half of all COVID infections in the US are now BA.5.

3 reasons why this isn't as alarming as it might seem:
- Rise in BA.5 has been gradual.
- Our immune systems are better prepared.
- Places hit first by the current wave have stabilized.

Some reasons for COVID optimism:
Gradual rise:

Whereas Omicron fully established itself in 1 month, BA.5 has taken 2 months to get to 50%.

And the size of the wave has been much smaller.

Meaning that any advantage BA.5 has over other subvariants is very small, compared to the advantage Omicron had over Delta.
Viruses evolve. But our immune systems also adapt.

One can always focus on the virus for bad news. But the overall trend is good news.

Apr-June 2022 was the least deadly 3-month period since the pandemic started. Even as transmission (e.g., test positivity, orange) has risen.
Read 8 tweets
Feb 25, 2022
New COVID guidance from CDC is out:


Now setting three "community levels". Previously based on cases + test positivity, now cases + new COVID admissions + % of hosp beds occupied by COVID.

A quick hot-take🧵on pros and cons of this approach.
Pro: It uses science.

This was based on measures that most accurately predicted deaths & ICU use in 3 weeks. Far better than arbitrary goals.
Pro: Test positivity was dropped.

% of tests positive is no longer a meaningful indicator, as testing varies so widely from one location to the next, and many tests are at-home tests that are difficult to track.
Read 10 tweets
Feb 11, 2022
What will COVID look like in 2022?

Nobody knows for sure, but here's my take on the 3 most likely scenarios.

Each with reasons why that scenario might (and might not) happen.

Take home: Depends on how long & strong immunity is, w/ most people now vax'd/infected multiple times.
Scenario A: 2022 is great.

COVID levels stay very low, at least until winter. Then we boost w/ COVID + flu vax.

Why so?
- Most people now have multiple doses of immunity (vax or infection).
- Many cases could be asymptomatic.
- Europe saw this in 2020 w much less immunity.
Why not Scenario A?
- Most countries haven't gone this long w/o a wave (or very stringent restrictions).
- Immunity vs infection doesn't seem to last that long: four vax doses haven't prevented a wave in Israel.
- Betting against the virus has not been smart so far.
Read 8 tweets
Feb 3, 2022
Some students have asked me: "If I want to engage w the press in my future job, what should I learn to do?"

Here's my top 10 list of responses to this question.

Bottom line: it's not about how smart you are.

Would welcome comments on this list from my journalist colleagues!
1. Treat journalists as allies, not adversaries.

Some scientists think journalists are looking for missteps that can be misquoted.

In my experience, this is not true. Journalists want to get the story right as much as we do.

Practice interviewing as friendly conversation.
2. Do your homework.

Don't go into an interview without asking what the story is about.

Spend a few minutes making sure your numbers are right. (I often keep tabs/notes open for reference.)

Think about the 2-3 key points you want to make, so you can make them repeatedly.
Read 11 tweets
Jan 24, 2022
Now that we've been living with Omicron for 2 months, we can use this wave to learn some lessons about
COVID in general.

First: This virus likely depends on a core group of people/settings for its spread.

We can surmise this by looking at the decline of Delta.
If 1 in 3 Omicron cases is reported, the # of cases in the US now is similar to # vax'd per day in April.

Yet Delta is falling much faster today (in winter) than cases were in April.

Why? Likely Omicron (unlike vax) is infecting the people who otherwise would transmit Delta.
And Omicron-induced immunity nearly wiped out Delta - at a time when <5% of the population had been infected w Omicron.

Meaning that a small fraction of people (those most likely to get infected & transmit) and settings
(large outbreak-prone gatherings) are sustaining spread.
Read 8 tweets
Jan 18, 2022
Though guilty myself, I wish we would stop naming waves according to variant ("delta wave", "omicron wave", etc).

This makes it seem like each wave is randomly triggered by a new variant - and there's nothing we can do about it.

But in reality, we are making a lot of progress.
Each wave can be explained by a combination of behavior change, winter effect, and immunity. Without invoking variants.

And though waning immunity has played a role so far, our overall immunity is building w time. (Why the average case now is milder than early in the pandemic.)
As shown below, we were able to live more freely in 2021. Largely because of vax/immunity.

This most recent wave isn't over - and we need to act w caution until it is.

But we are not at the mercy of each new variant. Though we're all tired, things should get better soon.
Read 4 tweets

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