BACKGROUND
Evolving infectious diseases are a continuing threat to public health, especially in democratic nations where persuasion is required to adjust population behavior to counter the threat. COVID-19 is particularly dangerous because one can be infected by inhaling air exhaled by an infectious person who may not even be symptomatic. Experience in 2020-2021 can be used to guide future control efforts.
OBJECTIVE
This investigation sought to understand the factors that controlled the development of the COVID-19 pandemic, particularly the highs and lows in death rates as they were influenced by government leaders and media.
METHODS
Published data on COVID-19 death rates in eight selected nations and eleven selected U.S. states for the period 1 Mar. 2020 through 31 May 2021 were compared with calculations using a Susceptible-Exposed-Infectious-Recovered (SEIR) model that included an adjustment of the population’s basic reproduction number, R0, in response to information.
RESULTS
The death rates attributed to COVID-19 exhibited high peaks in most of the developed democratic nations in March/April 2020 and Dec. 2020/Jan. 2021. Initial values of R0 as high as 5.0 were deduced from the growth curves. The plateau near 700 deaths per million population reached in the summer of 2020 mirrored the effects of herd immunity in the model, but seroprevalence surveys proved that the population immune fraction was too low. An average of 169 people tested positive for COVID-19 antibodies for each death, i.e., more than twice the number of reported “cases” in the U.S.
It was postulated that the March/April 2020 peak was primarily due to a ~20% fraction of the population that denied the threat and continued to interact normally. Nevertheless, toward the end of 2020 the general population relaxed its vigilance and another major peak in death rates occurred, even in areas that had suffered the most in the earlier peak. A reasonable selection of parameters for population response to information about “cases” and “deaths” produced the observed interval between peaks in the model and predicted a third peak in Sept. 2021 if less than 80% of the population were vaccinated.
CONCLUSIONS
Cyclic death waves are manifestations of a classical control loop with its feedback delayed by disease progression, political controversy, and natural population inertia.
The pandemic was prolonged in the U.S. because the population chose to keep R0 near 1.0 by relaxing restrictions once the death rate subsided.
If no social restrictions had been adopted while the quality of medical care was sustained, approximately 1.6 million deaths would have resulted in the U.S. The vaccine, although developed and deployed at record speed, was too late to ameliorate this result.
Trends and Geographic Patterns in Drug-Poisoning Death Rates in the U.S., 1999–2009