Missouri is one of several states currently experiencing significant increases in the number of new coronavirus cases. Since the Memorial Day holiday weekend, the number of confirmed cases increased by more than 5,700, according to surveillance data through June 20 from the Missouri Department of Health and Senior Services. This marked a four-week 44% increase, bringing the state total to 18,700 confirmed cases since the virus was first detected in Missouri in early March.
Fortunately, while confirmed cases have experienced new levels of growth in Missouri since May 23, hospitalizations and COVID-19-related deaths have continued to decline. Despite the aforementioned 44% increase in cases, during the same period, Missourians hospitalized with COVID-19 have dipped from an average of 694 per day during the week leading up to May 25 to 590 per day during the week of June 14. At the same time, daily COVID-19-related deaths have declined from nine to two statewide.
It may seem counterintuitive that Missouri is experiencing extreme growth in cases yet continued declines in both case-severity and mortality. However, analyzing data from the DHSS WebSurv syndromic surveillance system provides a probable explanation. In combination with social determinants of health and the presence of certain comorbid conditions, age is the single largest predictor of adverse outcomes related to COVID-19. Based on data from the largest single cohort study on COVID-19 to date, compared to individuals under age 50, people in their 60s are five times as likely to die from the disease. For individuals in their 70s, the proportional hazard increases to 8.5, while COVID-19 patients over age 80 face an 11-fold risk of death.
Missouri’s extreme growth in cases, and concurrent reductions in both hospitalization and mortality, can largely be explained by the age distribution of new cases in the state. At the peak of the surge in mid-April, the average age of Missourians with new COVID-19 cases was 56 years. On June 20, newly diagnosed COVID-19 patients were 38 years old on average. Missourians under age 45 make up 57% of the population – they’re also most likely to be exposed to COVID-19 by returning to work or participating in social events. During the first week of March, this cohort accounted for 23% of COVID-19 cases in the state. As of last week, they accounted for 63% of new cases.
The good news: These individuals’ youth is a strong protective factor — they’re typically without underlying comorbid risk factors, such as diabetes, heart and pulmonary disease, which lends resilience to fight off secondary lung infections. The bad news: They are more likely to be asymptomatic, and therefore, more likely to unintentionally share the virus with at-risk friends and relatives.
The latest epidemiological models are picking up on these signals — two weeks ago the reproductive rate, or R-naught, was sustainably below one in every region of the state. Last week, it was uniformly over one, including the southeastern region where each case
was estimated to share the virus with 1.4 contacts.
The data are beginning to tell the story of consequences related to changing policies and attitudes in Missouri. And while the story hasn’t yet matriculated into the chapter on adverse outcomes, it’s important to understand that hospitalization, and death in particular, lag significantly behind new cases. While the full story is still being written, these data underscore the importance of physical distancing and masking among all Missourians, and among “young invincibles” in particular.
A downloadable PDF with complete information, including graphs, is available.