EPI’s COVID-19 forecast model: June 8, 2020

Findings

Where are we now?

While daily reported cases have declined on average nationally between April and May, Florida’s daily reported cases continue to rise. The top chart shows the total case counts reported daily for the nation. The bottom chart graphs new daily cases in Florida. Rt is used by researchers to describe how fast a virus is spreading between people. It signals how many people will become infected, on average, by someone who is infectious. 

Two charts stacked on top of each other. The top chart shows the total case counts reported daily for the nation from February to May. The bottom chart graphs new daily cases in Florida from May 11, 2020, to June 1, 2020.
The charts compare the total cases reported per day in the United states and the total cases reported per day in Florida.

Current trend of COVID-19 deaths in Florida

Current reported deaths attributed to COVID-19 have declined since late April.

The line graph charts the current situation in Florida and short term projections of Covid-19 deaths in Florida from March 22, 2020, to June 22, 2020.
Short term projections for Covid-19 deaths in the state of Florida.

Current trend of COVID-19 infections in Florida

Despite the downward trend in reported deaths, our daily reported incidence of infection has continued to steadily rise.

The line graph charts the current situation in Florida and the short-term projections for COVID-19 infections in Florida from March 22, 2020, to August 22, 2020.
Short term projections for COVID-19 infections in the state of Florida.

Estimates of close contacts

This graph shows an estimate of Floridian’s typical daily close contacts. These contacts began decreasing shortly after a state of emergency was declared on March 9, 2020 and continued to decrease to about half of normal levels just after shelter-in-place orders were issued on April 4, 2020. Daily close contacts have been rising slowly but steadily since mid-April, but are not yet back to pre-pandemic typical levels.

A line graph that charts an estimate of the daily close contacts in Florida from February 02, 2020, to May 16, 2020.
Estimates of the daily close contacts that occur in the state of Florida.

Mobility in Florida

This graph shows an estimate of distance traveled by typical Floridians. Similar to the graph above, mobility began decreasing shortly after a state of emergency was declared on March 9, 2020. Mobility continued to decrease to below half of normal levels by the time shelter-in-place orders were issued on April 4, 2020. Daily mobility has risen slowly since mid-April, but it is not yet back to pre-pandemic typical levels.

A line graph charts the distance traveled by people in Florida from February 03, 2020, to May 16, 2020.
The estimate of distance traveled by people in the state of Florida.

Rate of spread

This chart shows an estimate for Rt. (This is a measure of how fast a virus is spreading between people. It describes how many people will become infected, on average, by someone who is infectious.) At the beginning of the pandemic, Rt in Florida was close to three but is now hovering slightly above one. This means that in March every infected person infected, on average, three more people; today, each infected person only spreads the virus to slightly more than one person. To halt the virus from spreading, Rt needs to fall below one.

This graph charts the estimate of how fast a virus spreads between people in Florida. Estimated currently 39,000 infectious people 95% CI [10,200-95,000] in Florida.
The estimate of how fast a virus spreads between people – number of people who will be infected, on average, by someone who is infectious.

Where is RT less than one? Not even close to one?

Green states have a high probability of Rt being less than one, which is a good thing (the darker the green, the higher the probability). Pink states have a low probability of Rt being less than one, which means their viral spread could be better controlled (the darker the pink, the less likely it is that Rt falls below one; it’s more likely equal to, or greater than, one in these states).

A colored map that charts the probability of a state to have a Rt (rate at which the virus spreads) of less than 1.
The chart depicts the the probability of a state to have a Rt (rate at which the virus spreads) of less than 1.

What’s the forecast for Fall 2020?

The best outcome to control Florida’s epidemic of COVID-19 is to do so much testing that at least 50% of symptomatic cases are caught. After these are identified, at least 20% of the contacts of each symptomatic person would need to be quarantined to reduce potential transmission.

The figure shows three line graphs that charts mitigation strategies during the second wave. Staged reopening testing with contact tracing results in a large second wave. With 50% symptomatic cases tested and 20% or more of the contacts of the defected symptomatic individuals are traced and put into quarantine, the epidemic is controlled.
The best outcome to control the spread of COVID-19 results from mass testing.

Context

What happened with swine flu?

Swine flu, known to the medical world as Influenza A subtype H1N1, swept through the U.S. between late summer 2009 and spring 2010. This is what the flu peaks looked like, from mid-2006 to early 2010. Note the much higher than normal peak in flu-like illnesses reported from mid-2009 to early 2010.

The line graph charts the percentage of visits for influenza-like illness (ILI) reported by the U.S. Outpatient Influenza-like Surveillance Network (ILINet). This weekly summary spans from October 1, 2006, to May 22, 2010.
A weekly influenza surveillance report prepared by the CDC influenza division.

But what about successive waves of outbreak?

Nearly 100 years before the swine flu, another much deadlier Influenza A subtype H1N1 swept through the U.S. The 1918 Spanish flu killed millions of people across the globe in several waves of infection. The second and thirds waves were far deadlier than the first.

A line graph charts the number of deaths per 1000 people in a population during the 1918 Spanish flu pandemic, notating the three waves.
The trajectory of the rate of deaths during the three waves of the 1918 Spanish flu pandemic.

What about a vaccine?

Safe and effective vaccines take time. We will hopefully have at least one viable vaccine candidate by this fall.

Vaccine development. Over 100 vaccines under development. WHO is launching a large, international randomized controlled clinical. Multiple vaccines adaptively evaluated. For each vaccine, the primary efficacy results are expected within 3-6 months of the vaccine entering the trial. We should have 1 or more efficacious vaccines identified by the end of September.
The state of a COVID-19 vaccine development.

What happens till then?

We need to rely on strict public health measures until a safe and effective vaccine is available for mass distribution.


Editor’s note: an earlier version of this webpage mistakenly stated, “The best outcome to control Florida’s epidemic of COVID-19 is to do so much testing that at least 50% of asymptomatic cases are caught. After these are identified, at least 20% of the contacts of each asymptomatic person would need to be quarantined to reduce potential transmission.” This was corrected on June 25th to read “50% of symptomatic cases” and “20% of the contacts of each symptomatic person…”


Ira M Longini

Ira M Longini

Professor
Department: PHHP-COM BIOSTATISTICS
Phone: (352) 294-1938