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Natalie E. Dean, PhD Profile picture
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11 Mar, 4 tweets, 2 min read
Ummm.... source for the tweet on the right? It has been retweeted by several big accounts, but I can't find any evidence for such a study.

Remember folks, verify your sources. I've seen a lot of misinformation floating around, particularly about Florida.
In times like this, I wish that Jason Salemi were still on Twitter so I could point you all to him, but I'll do my best in a few follow-on tweets.

Link to his great website:
covid19florida.mystrikingly.com
There are different ways to measure test positivity that result in modest differences. (Ignore the blue line of only people who have never been tested before, which is less useful at this stage of the pandemic.) Tracking trends is more useful than focusing on a raw number. Image
All states have some level of excess deaths due to the pandemic that are not captured in official statistics. Florida has not fared well, but neither have many other states. It is not an outlier in that way. Important to keep our criticisms fact-based.

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More from @nataliexdean

Natalie E. Dean, PhD Profile picture
3 Mar
Out today -- my piece in @nature on a topic I feel very strongly about = the need to coordinate and harmonize observational vaccine studies! If you think it is hard to compare vaccine trials, you haven't seen anything yet.
A thread. 1/6
nature.com/articles/d4158…
With randomized vaccine trials becoming increasingly challenging to conduct, we will rely on observational studies to guide important policy decisions. For example, these studies can help us understand the durability of vaccines or how well they work against new variants. 2/6
We can easily expect hundreds of separate observational vaccine studies, some conducted at only a single site. Each using different endpoints, covariates, eligibility, and so on. It will be extraordinarily hard to sort through these differences in meta-analyses. 3/6
Read 6 tweets
Natalie E. Dean, PhD Profile picture
17 Feb
THINK LIKE AN EPIDEMIOLOGIST: Lately I have been asked why we are seeing a dramatic turnaround in cases in the US. Is it vaccines? Herd immunity? An artifact due to a drop in testing? Behavior change? Weather?? A few tweets about how I step through this question. 1/6 Image
To start, I look to see whether the drop is an artifact. While testing has dropped somewhat, it's not enough to explain the rapid drop in cases. A drop in testing would also not explain the drop in hospitalizations that is consistent across regions. 2/6
covidtracking.com/data/charts ImageImage
I then consider the similarity of the drop across locations, looking by subregion and by state. The similar patterns seen are relevant because different places have different vaccination coverage, levels of acquired immunity, and weather. Why the turnaround at a similar time? 3/6 ImageImage
Read 7 tweets
Natalie E. Dean, PhD Profile picture
15 Feb
How do we measure how well the flu vaccine works every year? We use an observational study called the "test negative design." A few tweets on how it works, and why it will be a big part of ongoing COVID-19 vaccine evaluation. 1/8

Figure source: Fukushima et al. (2017) Vaccine
In the test negative design, individuals with disease symptoms seek healthcare and testing. If they test positive, they are TEST POSITIVE CASES. If they test negative (and their symptoms are caused by something else), they are TEST NEGATIVE CONTROLS. 2/8
We can then look back and see how many of the test positive cases were vaccinated, and how many of the test negative controls were unvaccinated. Where the vaccine works well, there won't be many vaccinated people testing positive. 3/8
Read 8 tweets
Natalie E. Dean, PhD Profile picture
8 Feb
Warning - some in-the-weeds tweets about vaccine efficacy trials, new strains, and decision making under uncertainty. I offer more questions than answers, but hopefully it can generate some discussion...
1/6
For COVID vaccine studies, we can imagine two goals:
(1) We aim to measure efficacy precisely (minimize uncertainty, regardless of the true efficacy), or
(2) We simplify our goal and try to measure if the vaccine is doing well enough - is efficacy above our success threshold? 2/6
This is relevant for discussions about how well vaccines are performing against different variants. For those who are already vaccinated, we want to know how well the vaccine works against a new strain. What is the efficacy, even if it is lower? This is like the first goal. 3/6
Read 6 tweets
Natalie E. Dean, PhD Profile picture
3 Feb
Oxford/AZ reports overall reduction in PCR positivity of 54.1%, but only 2% "vaccine efficacy against asymptomatic infection."

Confused?

Allow me to explain with crudely drawn pictures why the overall findings are still quite positive. 1/8
Let's start by imagining the base case (no vaccine). SARS-CoV-2 infections fall into a range of categories: severe, moderate, mild, or asymptomatic.
(Categories not perfectly to scale for all of this, don't @ me). 2/8
Vaccines protect against disease in two major ways.
- They can prevent infection entirely.
- Or they may not prevent infection, but they prep your immune system so that you don't develop symptoms. Usually it is some combination of the two. 3/8
Read 9 tweets
Natalie E. Dean, PhD Profile picture
29 Jan
With Novavax results, a welcome addition of another efficacious vaccine. The more, the merrier. Though the observed lower efficacy in South Africa is discouraging (and exactly how much lower is hard to tell given uncertainty), I’m glad we have these data in hand. 1/5
Well-conducted placebo controlled trials can give us the clearest read on how these vaccines are working against different variants. It was fortuitous to have these two trials in the UK and South Africa that we can compare in this way. We want to know what we’re dealing with. 2/5
Fortunately the vaccine is working well against the UK variant. But as we see in South Africa (and in laboratory studies with other vaccines), we cannot assume that vaccines are equally effective against all variants. We will need to continually monitor their effectiveness. 3/5
Read 5 tweets

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