According to a letter Gov. Newsom sent to President Trump, state models project that more than half of California’s population could become infected with the novel coronavirus over the next two months. (Shutterstock illustration)

Ask an Expert: How Solid Are California’s Coronavirus Projections?

Back CalMatters Mar 23, 2020 By Rachel Becker

State models project that more than half of the state could become infected with the novel coronavirus over the next two months, a threat to 22.5 million people that has prompted a statewide order from California Gov. Gavin Newsom to shelter in place except for essential activities.  

The California Department of Public Health reports that California’s case count has climbed, as of Monday, to 1,842 confirmed cases and 35 deaths — certainly an underestimate because of limited testing. Reports from across the state indicate that tests are being reserved for the sickest and most vulnerable because of a shortage in testing supplies that followed a slow federal rollout of tests hampered by technical flaws

So far, at least 25,200 tests have been conducted in California’s commercial, private, and public health laboratories. But nearly 12,700 of those results are still pending — leaving California in a data limbo, without a clear sense for how the epidemic is evolving. 

CalMatters spoke with Lee Riley, a professor of epidemiology and infectious diseases at the UC Berkeley School of Public Health and chair of the division of infectious diseases and vaccinology, to make sense of the numbers. 

This interview has been edited for clarity and brevity.  

Why is the novel coronavirus spreading so far, and so fast? 

We don’t really know why this is happening. But one of the observations being made in China, where they have a lot of experiences now, is that the virus seems to be able to transmit even before someone becomes symptomatic. 

And then even after an infected person recovers from the illness, they continue to shed the virus up to two weeks to even 20 days. So there’s more opportunity for an infected person to transmit. That’s why I think so many other people get infected — because there’s many more days of infectious period for a person to contract the virus. That may be one of the reasons that it’s spreading so quickly.

In a letter to President Donald Trump, Newsom said that the state projected that 56% of California might be infected with the novel coronavirus over 8 weeks — which means roughly 25.5 million Californians. Do those numbers make sense to you? 

I don’t have enough information about the source of the data that the governor is using to make any real comments. It’s not disclosed how those numbers were derived. The projection was probably made on not having the control measures that we currently have [such as Thursday’s shelter in place order]. If we didn’t do anything, then yes, certainly, we could have millions of people getting infected.

But we are doing things. And, I don’t know how people are behaving, but the fact that we’re not seeing the explosive increase in the number of deaths tells me that, number one, the healthcare providers are really doing a good job preventing deaths, and that measures that are being taken right now are working, at some level. 

How are the testing delays and shortages affecting those numbers?

One caveat is that these numbers that we’re getting may be somewhat delayed because as you know, the testing is increasing in number, and so there’s a real backlog of the tests. We don’t really know exactly what’s happening now. The numbers that we’re seeing are based on the tests that were done several days ago, and they’re just coming up because [at] a lot of the testing services, there’s a huge backlog right now. 

We don’t know which direction this is going to go. We may see a continued increase, a huge bump in the next several days, but that just means the results are just coming in. 

The governor’s projections that 56% of Californians might become infected, and that 20% might get sick enough to require hospitalization — can you put those numbers into context? Have we ever seen anything like it before?

If that’s true, that would be unprecedented. We always talk about the 1918 influenza epidemic, right? Even compared to that, this would be far greater in terms of the number. Mind you, when we talk about this level of infection, that doesn’t mean that all those people are going to have severe disease. 

The governor’s estimates are that maybe 20% will have disease severe enough to need hospitalization. That would still be a lot of hospitalizations, and that would overwhelm the healthcare infrastructure in California. 

What do you think of the state’s shelter in place directive — can it slow the spread of the epidemic? 

I think so. That is really, probably, the best strategy at this point, short of vaccines or other modalities. That’s what we really need to be doing. 

In Wuhan, in the province of Hubei, which is a large province in China with more people than California, they certainly didn’t have millions of infected people. The epidemic was put under control in about three months. So if we compare what happened in China to what’s happening in California, there’s a huge difference in terms of the projections that have been made. 

Although, one thing that should be stressed is that in China they had much more draconian control measures. They not only restricted international travel — people coming in to China or going out — but also intra-country travel. And so that may have also helped. The U.S. is a big country, and so far, and the U.S. hasn’t restricted intra-country travel, and even within California, we’re not really restricting travel between cities — although that’s probably going to happen anyways because people are being asked to stay in their homes. 

What do you think the future holds?

At some point, we need to start thinking about what we are going to do next year. Is the same thing going to happen again next year? If so, are we going to keep doing the same every year? We don’t know, and I think that’s important. More research needs to be done to really understand about the structure of this virus to see if this is a virus that’s going to become seasonal, or endemic [meaning it’s always around], or disappear, like the first SARS. So those are some of the issues we really need to start thinking about, and start planning for next year, and be prepared for next year. is a nonprofit, nonpartisan media venture explaining California policies and politics.


Visitor (not verified)March 23, 2020 - 5:23pm

I am sure that the governor of California's calculator added at least 2 zeros when he made his "25 Million" statement... and NO ONE CAUGHT IT AND THE NATIONAL MEDIA REPORTED IT!!!!!... The reason he hasn't released his model and the good doctor you quoted doesn't have the underlying data is doesn't exist!!!. This is simple math...25,000,000 divided by 56 days (8 weeks) means that California would have to have to have 446,000 new cases EVERY DAY FOR 56 DAYS to hit 25,000,000. There is no data in existence that supports that projection...there are only 380,000 cases ON EARTH right now after almost a month of reporting and testing!!!

My point is that we could have take less drastic measures and exercised common sense to protect and isolate the most vulnerable people in our population vs reducing the worlds 8th largest economy to ashes.

My numbers...
As of today, California cases are at 2100...that's a 1000 case increase in the last 5 days since our governor made his 25,000,000 prognostication...or just under 50% every 5 days. If that rate continues, there will be at...
3000 cases after 10 days...
4500 after 15 days...
6750 after 20 days...
10,125 after 25 days...
15,167 after 30 days...
22,760 after 35 days...
34,140 after 40 days...
51,210 after 45 days...
76,815 after 50 days...
115,222 after 55 days...
126,744 after 60 days.... double, triple or even multiply this number by 10 to compensate for whatever variable of "un-tested" or "worst case" you want... it's still off by about 24 million!!!!!

My Conclusion... 99% of California's population will NEVER get the virus... and of those that do, 90% will recover!!!

RELAX... stay "fact based and optimistic".