In response to the summer surge in infections in California, Governor Newsom re-instituted strict controls on July 1st closing most indoor businesses and then re-imposed a stay at home order on July 13th. We take a look at how effective these lockdown efforts were in controlling the spread of the virus.
A simple examination of Rt (reproductive rate over time) of CA from rt.live shows that there was little variation in July. Rt is directly proportional to the number of infectious contacts. If July lockdowns were effective in any significant sense we would see a marked decrease in Rt. We see very little movement. Rt was already decaying for several weeks prior to the governor’s actions, and for the month of July Rt was fairly flat. There is no correlation between these recent lockdown activities and a reduction in infectious contacts. The lockdown efforts have had little effect other than to kill small businesses.
Infectious Contacts INCREASED in July Despite Government Efforts
Using our CDM analysis toolset, we take a deeper look to assess mitigation effectiveness by adjusting dynamic contact trends across age groups and to match the actual death rate curves. We assume 50% asymptomatic rates for COVID-19 infections. A base simulation of 2 million discrete agents was used and results are scaling to the population of 39 million CA residents.
We would expect an overall reduction in connectivity (potentially infectious contacts) in July if CA lockdown efforts were effective. This assumption of was made in our previous analysis which understated death rates in August: California Roadmap for a Balanced Recovery. To match actual date of death trends, our current analysis shows that connectivity must have increased in July, despite the attempt to return to the lockdown state of March/April.
The original lockdown in March was effective at slowing the spread with large compliance and little mask usage, but since June, subsequent efforts, including emphasis on mask wearing, are having little effect on slowing the spread. In general this can be chalked up to mitigation fatigue and significant spread of the virus through means other than those under government control (private interactions, family events and socializing).
The government has limited control over people and is exerting disproportionate and punitive control over businesses and institutions with little effect, effectively flattening the economy without flattening the curve. Worse, the focus on protecting the entire population rather than the elderly and the vulnerable is likely resulting in more deaths.
To match the current death trends in California, the contact rates were increased in July in the model as shown below. By the end of August, we estimate close to 24% of the population has been infected, and close to 33% of the 20-40 year old age group. Significant progress has been made towards the HIT and the infection velocity is naturally slowing.
Date of Death Extraction
Determination of actual date of death is critical to calibration of the analysis. The graph below shows the derived date of death the reported death date data sets found at the COVID Tracking Project. Our approach is far more accurate than a rolling average of reported deaths and is detailed here: Reported versus Actual Date of Death. The most recent 2 weeks represent incomplete counts.
CA is Approaching Herd Immunity
Despite punitive government efforts, the virus will inevitably spread among younger and middle age adults until we eventually hit the herd immunity threshold (HIT) and then die out. Our analysis in general shows that the HIT is established when approximately 25% to 30% of the population is infected and 40% to 50% of the young adult cohort (for more information see our article: Are We Closer to Herd Immunity than Most Experts Say?.
New infections peaked in early August, despite overall increasing connectivity. Remember current connectivity is still much lower than the pre-COVID-19 baseline and as such the HIT is significantly lower. Connectivity can be increasing and infections can still be in decline.
Overall, California is on a path to reach the HIT threshold this fall. This trend is similar to what we have seen in Florida, Texas and Arizona where the disease is now in steep decline. Infection distributions that show there is more mobility in younger cohorts, as would be expected, as risk for COVID death is minimal for young people and middle age adults.