Local leaders are looking at four different coronavirus models as they wrestle with when and how to lift San Antonio’s stay-at-home orders.
In briefings this week, San Antonio Metropolitan Health District officials said they are relying on models by the University of Washington’s Institute for Health Metrics and Evaluation, international consulting firm Oliver Wyman, and two by the University of Texas at San Antonio.
None of the models offer sunny predictions for a normal summer without government-imposed shutdowns. The two UTSA models indicate that if all restrictions are lifted immediately and people go back to business as usual, it could lead to hundreds of thousands of total cases in San Antonio in the next couple of months.
“All models, in this moment, coincide with one thing: if we lift measures and we go back to life as usual, this thing will bounce back quickly,” said Juan Gutiérrez, chair of UTSA’s mathematics department, who led the development of one model.
But if the current restrictions remain in place, Gutiérrez’s team’s model projects that the number of cases in San Antonio will hit a peak in early May of 700 active cases, with a total of 3,600 through July.
The broader models created by the University of Washington and Oliver Wyman teams are more focused on the world’s current trajectory under the shutdowns. After governors and local authorities across the U.S. clamped down on in-person gatherings and movement, forecasters revised the model last week down from approximately 81,000 deaths predicted across the U.S. to a little more than 60,000.
However, both of these models only make predictions through the summer, a period many epidemiologists say will mark the first of several outbreaks in the U.S.
Sam Glick, a San Francisco-based health and life sciences partner for Oliver Wyman, said his firm’s model is focused on the “first peak” of cases. The country could end up seeing three or four peaks before a vaccine is widespread, he said.
“By and large, it seems that the containment measures in the U.S. are working,” Glick said. “The real interest is in what that next peak is and how much we can let up.”
That’s the difficult question facing San Antonio Mayor Ron Nirenberg and Bexar County Judge Nelson Wolff. This week, the two said they intend to form a task force to focus on how officials could begin unwinding social distancing orders and begin to restart the local economy.
“We have been clear that any talk of opening back up is premature without the parameters being laid out by the medical community,” Nirenberg said in a Wednesday briefing. “What we want to make sure is we’ve got the right ground rules in place from the public health and medical perspective before we make those decisions.
Doing so will mean weighing risks and coping with vast uncertainty. Each of the four models posted on the City’s page draws different conclusions based on different assumptions and, in some cases, different data.
That’s why Assistant City Manager and former Metro Health Director Colleen Bridger has compared them to hurricane spaghetti models, which often show a huge range of coastal cities that could take a direct hit from an oncoming storm.
Oliver Wyman’s model shows forecasts down to the county level. It predicts that Bexar County will see around 1,700 total cases and a peak of around 930 active cases in late April. Active cases exclude people who have recovered or died.
The University of Washington model is focused on the availability of hospital beds, intensive care beds, and ventilators at the state level. For Texas, it predicts that these needs will be greatest around May 1 and that the health care system in the state is not likely to be overwhelmed.
However, it also shows a huge range of values to indicate uncertainty. At the outbreak’s peak, the state will need anywhere from 140 to more than 2,000 intensive care beds and 120 to 1,800 ventilators, according to the model’s projections.
The City also posted the results of a separate UTSA model led by Dhireesha Kudithipudi, a computer engineering professor and director of the university’s Neuromorphic AI Lab. That lab’s model uses real-time location data from Google showing human movement around the city before and after the shutdown.
That study predicts a peak of nearly 2,000 coronavirus cases by mid-May with a total of 30,000 cases by mid-August if current measures stay in place. If they’re lifted, cases could soar into the hundreds of thousands.
All of the models rely on different assumptions, such as how quickly the virus spreads, which populations are affected first, and what restrictions governments leave in place. All likely underestimate the true number of positive cases because of testing shortages across the U.S. and a lack of testing for potential carriers who don’t show symptoms.
“We are certainly underestimating the real number of cases that exist in the environment,” Glick said.
For Gutiérrez, modeling the effects of coronavirus has been informed by decades studying infectious disease at the University of Georgia in Atlanta, also home to the U.S. Centers for Disease Control and Prevention. Earlier this year, he and his co-authors published a model they created for malaria that shows the influence of asymptomatic carriers.
In a phone interview Wednesday, Gutiérrez said coronavirus spreads “like wildfire” around the world because it’s being driven by people who show no symptoms.
“These are the group of people who keep transmitting the disease in the community,” Gutiérrez said. This also applies to those who do have symptoms but avoid testing and treatment because they might not be able to afford health care.
“If you have a job in which you are paid by the hour, and if you don’t work, you don’t eat, what are you going to do if you get sick?” Gutiérrez said. “You just keep going.”
That could be a serious issue in San Antonio, where income and health care access differ significantly in different portions of the city. San Antonio’s coronavirus cases have so far been largely clustered in higher-income zip codes, where more people have likely had access to testing.
Metro Health officials say they have responded to this by loosening requirements for testing at San Antonio’s mass testing site at Freeman Coliseum and by doing outreach campaigns focused on parts of the city where there is a lack of testing.
With the number of cases here below 1,000 and relatively few people hospitalized, the situation seems less severe in San Antonio for now. Gutiérrez said that reflects local leadership acting at the right time.
“Had we delayed one single week the response from the City, the number of cases would have been in the thousands in this moment,” Gutiérrez said.