Caitlin Rivers, PhD Profile picture
Infectious disease epidemiologist. Faculty at Johns Hopkins Center for Health Security (@JHSPH_CHS).
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27 Jul
There may be confusion today about what CDC's new mask guidance means about the protection of vaccination. There are multiple levels of protection, and it’s important to know which level is up for discussion. Quick review. 1/6
1. Any infection. If you are vaccinated, would your body fight off the virus so that you would never even test positive or become infectious? This scenario is what original CDC guidance allowing vaxxed people to unmask was banking on being most common. 2/…
2 Asymptomatic or presymptomatic infection and infectiousness. Say you get infected and would test positive but you have no symptoms. Could you transmit? We don’t rly know how common this is. Masks have particular value here because most people would not know they are infected 3/
Read 7 tweets
21 Jul
Time to return to indoor mask policies in states that are surging. It happened sooner than I expected, but when hospitalization trends look like this, something has to change.
Yes, it's perhaps unfair to vaccinated people, but with no way to differentiate a policy for all is the only practical way.
We also need to ramp up testing (again) and carefully prepare for school reopening. Mitigation measures must remain in schools: masks, ventilation, access to testing.
Read 5 tweets
14 Apr
One in a million will not be the final estimate for the unconfirmed J&J events and I think we should be cautious in citing it. The incidence will surely be rare, but @C_R_Watson and I wrote about biases in estimating mortality last Feb, and similar issues are in play here 1/
@C_R_Watson First, the numerator. Now that awareness has been raised, more cases may be reported. 2/…
Second, the denominator. All of the cases in US have been in women ages 18-48. It is reasonable to ask whether the denominator should reflect that. The expert committee will consider this. 3/
Read 5 tweets
29 Mar
Cases are on the rise in many states. How worried am I? I am concerned, but not as much as I would have been 6 months ago with these trends. Short thread. 1/
Many states are doing quite well. I would like to see cases fall below 20 cases per 100,000 per day as a first goal and 10 as a second goal (and then the lower the better). By that measure, we are doing ok: 35 states are at or below 20 and 12 are below 10. 2/
Yet some states are resurging. MI and NJ are at ~50 cases per 100,000 per day and hosp rising too. Risk in those states is high, and leaders should intervene by closing high risk settings and accelerating vaccination. Fed govt could help by sending extra vax coming online. 3/
Read 7 tweets
4 Feb
So, how are we doing with covid? Nationally, reported incidence has fallen from around 76 cases per 100,000 population per day to about 43. Better! But not yet good. Thresholds are contentious, but I think 20 as a first goal and 10 as a second goal are reasonable to start. 1/
Nationally, those thresholds correspond to approx. 66,000 and 33,000 daily cases, respectively. Right now, we’re at ~140,000 cases reported each day on average, so we need to more than halve incidence to get to Goal 1. 2/
What do 20 and 10 cases per 100,000 per day get you, practically? We will still be masking and distancing, for sure. In VT, where reported incidence is currently about 21, in a group of 10 people there is about a 10% chance someone has covid (caveat ahead) 3/
Read 7 tweets
1 Feb
Fantastic development. This test is already authorized for home use without a prescription, including in children and people without symptoms. Increasing supply critical to allow people to easily access tests.
The test was authorized in Dec but supplies are limited. The Biden Admin is investing in expanding manufacturing capacity. It will take a while (months, probably) for that to result in more supply available to consumers, but we'll need tests for a long time so still useful.
The ~$30 price point is a little high to keep a few in the bathroom cabinet, but it will be a nice option. Looks like the Federal government will keep some of the supply, will be interesting to see how they are deployed.…
Read 4 tweets
21 Jan
I could not be more thrilled that the Biden-Harris Administration has announced an intention to create a National Center for Epidemic Forecasting and Outbreak Analytics @dylanbgeorge 1/…
@dylanbgeorge This idea has a long history, with dozens of brilliant scientists, policymakers and innovators behind the wheel, including many who roll up their sleeves every day to make sure our leaders have what they need to fight outbreaks effectively @dylanbgeorge 2/…
But they shouldn’t have to self-organize or do this on a volunteer basis. We need a standing capability that can advance the science by creating and improve epidemic models and outbreak analytics… @dylanbgeorge 3/…
Read 6 tweets
18 Jan
There are around 30 big counties, with a combined population of over 12 million, where upwards of 40% of the population has been infected. It's stunning how hard the pandemic has hit part of the US.

Estimates from…
% total infected is a modeled number that tries to estimate missed cases. You can read more here:… @youyanggu
Many of these counties have large institutions like prisons and jails, universities, and manufacturing or food production facilities. The NYT keeps a useful list of outbreaks in group settings.…
Read 4 tweets
4 Sep 20
I’m volunteering w/ the Covid-19 Symptom Data Challenge. Colleagues at CMU and UMD have been surveying people (e.g. on Facebook) whether they or people they know have covid-like symptoms. The goal is to explore how this data can be useful for tracking the virus. 1/
The CMU team has some analyses exploring uses for the data. They found, for example, an association between covid-like illness and covid incidence at the state level in July. 2/ Image
This seems promising at the county level as well, but there is a lot more exploration of the data to be done. What else can we do with this data, and how can it be useful to inform public health? That’s what the challenge is about – data discovery for public health. 3/
Read 5 tweets
7 Aug 20
Today I had the honor of testifying on reopening K12 schools for the House Select Committee on the Coronavirus Crisis. Here is what I said. 1/
It was exactly 3 mos ago that I last testified - we had 25-30k cases and >2k deaths daily. I said then that I feared complacency, that we would become numb to the crisis and would again create the conditions that led to us being the worst affected country in the world. 2/
Since then, we have new therapies, we’ve made progress on finding a vaccine, and many more tests are available. But in other ways, the complacency I feared has come to pass. We have 55k+ new cases daily, and deaths are again rising. 3/
Read 13 tweets
29 Jul 20
If I told you in March or April that we would still have a 60-70k daily cases in July, what would you think? Now carry that forward. Where do we want to be in Sep, Oct, Nov & how do we get there? Answering that question has to be priority #1. It's time to reset the US response 1/
Colleagues and I are out with a new report today with 10 recommendations for how the US should chart a new course. Here’s a thread with a quick rundown of the 10 -…
1. Encourage and, where appropriate, mandate things like physical distancing, masks, and limit on indoor gatherings. Without these measures in place, it will be difficult to maintain control of an outbreak or turn the corner on an outbreak that is accelerating.
Read 13 tweets
24 Jul 20
Second thread. The way I see it, two different things are happening related to CDC and schools. First, there was a lot useful material released today. There are decision tools and checklists for parents, guidance on mitigation measures, and more epi.…
This is the work of the brilliant CDC scientists who have devoted their lives to improving public health, and it is the CDC we need front and center in this time of crisis. 2/
And then there was the statement on “the importance of reopening America’s Schools in the Fall” which motivated my last thread. If I had an edit button I make clearer that my comments are about the statement. The other guidance is more substantive. 3/
Read 5 tweets
24 Jul 20
CDC just published a doc purporting to weigh the public health risks and education benefits of reopening schools. Having recently participated in a National Academies of Science committee on just that, I am not impressed at the paucity of this document 1/…
Covid is the reason schools were closed. It should be central to decisions about reopening in-person. To do otherwise is unfair to our families, teachers & communities. That doesn’t mean schools can’t open in person. But this is a weighty decision that deserves careful thought 2/
There is almost no epidemiology in this. There are only 2 paras on the science, and one of those is mostly devoted to flu. Consideration given to 1) the role of kids in transmission both in school and the broader community and 2) the risk of severe disease is nearly absent 3/
Read 10 tweets
9 Jul 20
I want to gently point out that voices on twitter, even experts, usually do not have any affiliation to one another. If you follow a lot of different experts, you might get a lot of different opinions, particularly on issues where evidence is mixed or absent. 1/
It is institutions e.g. CDC that coordinate the messages of the people who speak on their behalf so that everything is clear, consistent and trusted. We haven’t been able to hear from them as much as we would all like, and that has left a gap. 2/
I don’t mean to suggest that those of us who are active on twitter and in the media don’t take our duty to communicate seriously or that there is no room to improve. I feel a lot of responsibility, and I know others do as well. 3/
Read 4 tweets
28 Jun 20
80% of US adults report wearing a mask all, most, or some of the time when in stores or other businesses. Only 7% say they never do.… Image
87% of adults say the actions of ordinary Americans affect how the coronavirus spreads in the US a great deal or a fair amount. Only 2% say not at all.… Image
Even in the respondent groups least likely to say they wear a mask all or most of the time, uptake is still three quarters.… Image
Read 4 tweets
27 Jun 20
South Carolina reported 1,599 cases today, a new high. The percent of tests that come back positive is now nearly 20%, up from <10% earlier this month.
Florida registered almost 10,000 new cases today. The percent of tests positive is well into the teens, despite dramatic increases in testing capacity.
In Texas the percent of tests that are positive is now over 13%, up from a low of 4% at the end of May. About 5,500-6,000 new cases each day over the last 5 days.
Read 6 tweets
24 Jun 20
At the national level, we are clocking case counts reminiscent of April. This is bad news - we are headed in the wrong direction. In 3 of the last 5 days we’ve registered over 30k per day. 1/
Yes I am aware that testing turns up more cases. That is indeed the point. But in many of the states experiencing a resurgence, hospitalizations are up and the percent of tests that are positive is rising. Those are signs of trouble. 2/
I am concerned about states where the outbreak is accelerating. TX, AZ, SC, OK, OR are looking troubling. In AZ, ICU capacity is down to 16% and % positive is up to 20%. In TX, the # of people hospitalized is up from 1,756 on June 1 to 4,092 yesterday. It’s not just testing. 3/
Read 8 tweets
22 Jun 20
On the decision to reclose when an outbreak is intensifying. Let me first say that nobody wants to reclose. It is a drastic, disruptive move, to understate it. But we’re in a historic pandemic and when you need to break chains of transmission in a hurry, it’s an effective tool 1/
Why would a jurisdiction need to reclose? Principally if healthcare systems are at high risk of being overwhelmed. Wuhan, Lombardy, NYC illustrate how devastating that scenario can be, and it must be avoided. 2/
But the decision cannot wait until health systems are already overwhelmed. The time from infection to ICU admission is about 3 weeks, so any changes today will not show up in the data for about that long. That’s a long time when you’re headed in the wrong direction. 3/
Read 7 tweets
17 Jun 20
It's not a second wave. We never got through the first wave. It's more like a mesa. Image
It varies, of course. Some places are doing well. NY, NJ. Some are not - everywhere in red. The places in red. Miles to go before we sleep, as @JeromeAdamsMD once tweeted. Image
Link to excellent NYT data that I visit daily…
Read 4 tweets
1 Jun 20
I’m not usually a reactive tweeter but this caught me off guard yesterday. I wrote “wait, that can’t be the plan.” 1/
And then I deleted it because I wasn’t prepared to explain my thinking and it’s not fair to just throw that out without a justification. But now I am ready. Thanks @nataliexdean for sending the Hancock tweet. 2/
The actual change in guidance is that medically vulnerable people in the UK are allowed to go out to meet one other person, with proper social distancing. This is ok, I guess. One new contact, with distancing and masks, is lower on the spectrum of risks. Especially if outside 3/
Read 16 tweets
28 May 20
Tonight I am mourning the loss of 100,000 members of our families and communities. Each of those people had a biography. Wild adventures, funny anecdotes, selfless sacrifices, vices, heartbreaks. They will be missed and their memories will be cherished by those who loved them. 1/
This pandemic will live in the history books as one of the worst public health crises ever. Nearly a third of recorded deaths worldwide are in the United States. The scale of our disaster is staggering, and we are still in the midst. 2/
I remember after 9/11 the painful, sorrowful, beautiful, unifying national remembrances. Covid victims deserve that too. My fear is that we will rush to “get past” the pandemic. That we will never stop to collectively mourn those lost. 3/
Read 5 tweets