Not every SARS-CoV-2 infection in the COVID-19 pandemic is equal. Young people near all shrug off infection with a few weeks of inconvenience at worst. Old people, on the other hand, exhibit more significant illness and a high mortality rate. That mortality rate increases with both advancing age and the presence of inflammatory age-related chronic disease. The average 20 year old has a radically different risk profile when compared to the average 80 year old. This is one of the reasons why the commonly presented data, estimated infections per capita, or detected infections over time, is unhelpful. It needs the context of the age of the patients.
The popular media shows no inclination to correctly present SARS-CoV-2 as being a meaningful threat only to older people, tending to focus on overall infection counts, as well as on the tiny number of young people who are greatly impacted or killed by SARS-CoV-2. Meanwhile, the scientific community continues to publish papers that state the obvious on this topic. Viral infection disproportionately harms old people because of immunosenescence and inflammaging, the age-related decline in immune system competence and function. The best way to address the problem of mortality due to infectious disease in the elderly is to build therapies that can restore immune function.
There are many plausible approaches to improved immune function in the old. Regrowing the thymus. Improving hematopoietic stem cell function. Clearing out malfunctioning or damaged populations of immune cells. Regenerating fibrotic lymph nodes. A great deal more funding and effort should be directed towards these goals than is presently the case.
The majority of COVID-19 cases are mild. Some people may not have any clinical manifestation at all after SARS-CoV-2 infection. These asymptomatic individuals can serve as a source of virus spread. A report of the data in New York State up to March 31, 2020 showed that 47,326 persons out of 141,495 were tested positive (33%) for COVID-19, and many of those positives were asymptomatic. However, more surveillance data are needed to evaluate the extent of asymptomatic infection. In an infectious disease as heterogeneous as COVID-19, host factors are the key to determine disease severity and progression. For severe COVID-19 disease, major risk factors include age, male sex, obesity, smoking, and comorbid chronic conditions such as hypertension, type 2 diabetes mellitus, and others. Overwhelming evidence from around the world suggests that age itself is the most significant risk factor for severe COVID-19 disease and its adverse health outcomes.
Early data from China demonstrate that case fatality ratio (CFR) of COVID-19 increases with age, from 0.4% or lower in patients aged in the 40s or younger, 1.3% among those in their 50s, 3.6% in their 60s, 8% in their 70s, to 14.8% in their 80s or older; the overall CFR is 2.3%. In comparison, the overall CFR was approximately 2.8% worldwide and 2.7% in the US as of October 19, 2020. A more profound effect of aging is shown by COVID-19 CFR data from Italy, the first country affected by the pandemic after China. Again, CFRs are from less than 0.4% or lower in patients aged in the 40s or younger, 1% among those in their 50s, 3.5% in their 60s, 12.8% in their 70s, to 20.2% in their 80s and above; the overall CFR is 7.2%. Of note, the overall CFR is higher in Italy than that in China (7.2% vs 2.3%, respectively). This is likely because Italy not only has a higher CFR than China among adults over 70 years of age, but also has a higher proportion of older adults than China (22.8% vs 11.9%, respectively).
Data reported by the US Center for Disease Control and Prevention (CDC) also demonstrate significantly higher rates of hospitalizations, ICU admissions, and deaths secondary to COVID-19 among older adults (older then 65 years) than any younger age groups. Perhaps, the most striking evidence is the data on COVID-19 cases and death in nursing homes across the US. Currently, there are up to 1.5 million nursing home residents in the US, less than 0.5% of its population. However, about 7% of confirmed COVID-19 cases were among these vulnerable elderly individuals. Moreover, they suffered 40% of COVID deaths in the US. Taken together, it is unmistakable that aging is an important risk factor for severe COVID-19 disease and its adverse health outcomes including hospitalization, ICU admission, and death.