Sunday, April 5, 2020

Reasons for Hope: Lessons from Ohio and Washington

A close look at COVID-19 in Ohio and Washington can tell us what kind of measures are needed to contain the COVID-19 epidemic.  Check out the graph of new daily COVID-19 cases below:
New COVID-10 cases per day (5-day average smoothed)
New cases in Washington were growing at an accelerating rate until 3/29, but the dropped and remained between 400 and 500 per day. In contrast, the new cases in Ohio increased during the entire period.

Linear plots can sometimes be a bit deceiving, so let's look at a logarithmic plot of the same data:
We can see that the slope of the curve for Ohio got flatter over time; this indicates that the containment measures had some effect. However, only the measures in Washington, but not in Ohio, were sufficient to stabilize the number of new cases. What causes the difference? 

Not all stay home orders are equal

In both states, governors issued "stay home" orders within a day from each other: Ohio on March 22, and Washington on March 23. We cannot expect to see the effect of such orders on reported COVID-19 cases right away: the incubation time of the virus adds a 5-day delay, and testing and reporting adds another couple of days. Indeed we can see a one-week delay in the curves! For the effect for Washington is very obvious. In contrast, the effect for Ohio is more limited: we can see a small reduction in the slope of the curve in the logarithmic plot.

There are several possible reasons for the observed discrepancies, but I believe that the primary reason are differences in the stay-home orders that appear subtle, but have profound impact in the epidemic. This is supported by the analysis of stay-home orders and their effect in multiple other states and countries; I am merely using Washington and Ohio as an example.

Differences in the stay-at-home orders between Washington and Ohio

While both states order people to stay at home "when possible", they differ significantly in important details. Here are some of the major differences:
  • Restrictions on public meetings:
    • Washington: "all people in Washington State are immediately prohibited from participating in public and private gatherings of any number of people for social, spiritual and recreational purposes"
    • Ohio: "Any gathering of more than ten people unless exempted by this order" 
  • Definition of "essential businesses":
    • Washington: A relatively narrow definition is used that excludes, for example, most construction.  
    • Ohio: Uses a wide definition that states multiple times that categories "shall be construed broadly". The list of "essential businesses and operations includes virtually all manufacturing, sales, and supply, as well as "religious entities, gatherings, weddings, and funerals". 
  • Enforcement:
    • Washington: "Violators of this of this order may be subject to criminal penalties pursuant to RCW 43.06.220(5)"
    • Ohio: Does not mention any enforcement or penalties in the order. 
Overall, the Washington order is much stricter than the Ohio order. Ohio allows many business to keep operating that would not be allowed to operate in Washington; allows public meetings of up to 10 people; and has no provisions to enforce the regulations, which is likely to affect compliance to the order. Each "relaxation" of rules enables more infections, and makes containing the epidemic more difficult or impossible.

Regulations in other states and countries

From the Washington and Ohio example, it appears that stay-home-orders must (a) be strict, with only an absolute minimum of exceptions, and (b) must be enforced. But we need to look at other states and countries to see if this is the case in general. For this, the following approach can be used:
  1. States or countries must have implemented "stay-home" orders at least 10 days ago.
  2. The effect is evaluated by looking at the daily new cases. Effective orders show a typical pattern of a drop for a day or two, followed by a slight increase and then (relatively) constant numbers.
In Massachusetts, the governor issued an emergency order to businesses on March 23, but limited most instructions for the general public to an "advisory". The order "prohibits gatherings of more than 10 people, but allows larger meetings in "an unenclosed, outdoor space". The definition of "essential services" includes construction workers and many stores, including "hardware and building materials stores, consumer electronics, technology and appliances retail". Enforcement by the Department of Public Health is mentioned. So far, the actions have had only a limited effect on new COVID-19 cases:
In Germany, chancellor Angela Merkel appealed to the public to stay home on March 12. Public meetings of more than 2 people were prohibited on March 22, and the rules are enforced by the police with fines of up to 25,000 Euro. From the daily new case numbers, it appears that Merkel's talk had a pronounced, but temporary, effect. The stricter measures from March 23 caused a second drop followed by a stabilization of new case numbers:

Good news and better news

The analysis above provides good news: current measures to contain the COVID-19 epidemic do work, and a complete shutdown like in Italy and Spain is not needed. However, the effect of voluntary rules with broad exceptions is limited. While it reduces the daily grows in new case numbers, it does not stop it, and more new cases are added every day.

In contrast, regulation that are (a) mandatory, (b) enforced, (c) prohibit public meetings of more than 2 people, and (d) limit exceptions for business operations, can succeed in stabilizing the epidemic, so that the number of new daily cases remains constant.

To contain the epidemic, we can formulate three goals:
  1. Slow the exponential growth (reduce the increase in daily new cases).
  2. Stabilize the epidemic (keep daily new cases at a constant level).
  3. Stop the epidemic (make the number of daily new cases drop every day).
The first two steps are just stepping stones towards the first step, but accomplishing them is important. In epidemiological terms, the goals can be formulated as:
  1. Reduce the reproduction rate R noticeably (for example from 3 to 1.5).
  2. Reduce R further to a value close to 1. 
  3. Reduce R to less than 1.0.
Current measures as implemented in Ohio achieve the first goal. Stricter measures like in Washington achieve the second goal. From there, relative straightforward measures like the general use of facemasks in public may be sufficient to achieve the final goal of stopping the COVID-19 epidemic. Only then can we think about how to control COVID-19 until vaccines become available, and re-start the economy.

Update: Oregon sets the standard

Added 4-5-2020 9:40 pm:
Shortly after I posted a link to this post on Facebook, by FB friend Barton looked at cases in Oregon, and created this figure:
So Oregon also has stabilized the number of new cases. What is fantastic about this is that Oregon's governor, Kate Brown, issued a strict order on March 23, when there were fewer than 200 confirmed cases in Oregon. Oregon also has one of the lowest positive ratios in tests I have seen yet (about 6%), which indicates they test a lot. The "stay home" executive order has all the elements I mentioned as a "should have", and a few good ones I never heard of that others should copy. Companies that stay open must designate a "social distancing officer" who enforces social distancing and other restrictions. Businesses that fail to comply will be closed. There are several other executive orders that address other COVID-19 measures, too. Other states should take this as an example!

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