The novel Coronavirus primarily afflicts the elderly, with people over 65 at a higher risk for severe disease and death: At least that was the message coming out of China and Italy, lulling people who don’t fall into that category into a false sense of complacency.
But as the virus has besieged U.S. soil in recent weeks, topping 200,000 cases and over 4,500 deaths as of April 1, more and more stories have emerged of young people in critical condition and, in rare cases, even dying from Covid-19.
There’s the 30-year-old high school baseball coach in New Jersey, the 36-year-old principal in Brooklyn, a 25-year-old pharmacy technician in San Diego — all dead after testing positive for the novel coronavirus.
“It’s really important to look at those younger patients because it’s something that’s driving a lot of panic,” Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, said during a media session organized by the Association of Health Care Journalists. “If you hear about an 18-year-old dying, it’s much different than hearing about an 81-year-old dying.”
Young people can get seriously sick, but deaths are rare
Anecdotes about young people dying do not make data, however, and according to the latest numbers from the Centers for Disease Control and Prevention (CDC), U.S. death rates in children and younger adults are actually on par with Italy, Spain, China, and South Korea. Across those four countries, there have been two deaths reported in people under the age of 20, and fatality rates range from 0.1% to 0.4% in adults between the ages of 20 and 49.
“It’s really important that we figure out what the risk factors for death are in those younger age cohorts so that we can demystify it, so it’s not a lightning bolt from heaven that struck somebody down.”
The CDC grouped their age ranges differently, but the numbers are quite similar. As of March 18, there were zero deaths in people under the age of 20 (two deaths in teenagers have since been reported) and a fatality rate of 0.2% in people aged 20 to 44.
Even in New York City, the epicenter of the U.S. coronavirus outbreak, the numbers are only slightly higher, with one death in someone under the age of 18 and a fatality rate of 0.4% in people between the ages of 18 and 44.
This doesn’t mean younger adults aren’t getting seriously sick. In the U.S., 12% of all Covid-19 cases have been hospitalized, and 18% of those admitted were between the ages of 20 and 44. Reports from Spain show similar numbers, with 18.5% of hospitalized cases occurring in people under the age of 50. However, these twenty-, thirty-, and forty something are more likely to recover and eventually be sent home than their older relatives.
The question remains, though: Why are some young people getting so ill, and what’s different in those who do end up dying?
“There are going to be individuals that are younger, for whatever reason, maybe idiosyncrasies in their immune system or their genetics, that are going to be prone to severe infection,” Adalja said. “It’s really important that we figure out what the risk factors for death are in those younger age cohorts so that we can demystify it, so it’s not a lightning bolt from heaven that struck somebody down.”
Underlying medical conditions put 41.4 million U.S. adults between 18 and 64 at higher risk
There’s now emerging evidence that what matters even more than age are pre-existing conditions. According to a new report from the CDC published on March 31, 73% of people hospitalized for the novel coronavirus had at least one pre-existing condition. Even more striking, 94% of all people who died from the virus had an underlying chronic illness, the most common being diabetes, chronic lung disease, and cardiovascular disease.
Older people are more likely to have chronic health problems than younger individuals, which contributes to the age skew seen in deaths and severe cases. But according to an April 1 report from Kaiser Health News, there are still 41.4 million U.S. adults under the age of 65 who are at risk of developing a serious Covid-19 infection because of pre-existing conditions.
Recent evidence from Louisiana and Mississippi backs up this finding. The states are now two of the hardest hit, with the highest fatality rate in the U.S. coming from the New Orleans hotspot, and the highest hospitalization rate occurring in Mississippi. The two states also rank among the top four in the U.S. in terms of obesity and diabetes and in the top six for hypertension.
A new study from China published in The Lancet on April 1 suggests that obesity, especially in men, more than doubles the risk of developing severe pneumonia in people with Covid-19.
Why would these health conditions, which aren’t typically associated with respiratory problems, make the virus more deadly? There is mounting evidence that one of the primary ways people are dying from Covid-19 is cardiovascular complications, and obesity, diabetes, and hypertension can all place additional strain on the heart.
“It’s not a surprise that this virus affects the heart, it’s kind of expected, but the amount that it affects it is remarkable,” says Mohammad Madjid, MD, an assistant professor at McGovern Medical School at UTHealth in Houston, who’s been studying the effect of viruses on the heart for 20 years. “People with heart disease are particularly susceptible to it. People who have risk factors for heart disease — like hypertension, diabetes, old age, and smokers — they are particularly susceptible to it, too.”
It turns out that many deaths caused by respiratory infections, including influenza, are a result of damage to the heart, not the lungs, and Covid-19 appears to be no different. A recent study published in the Journal of the American Medical Association showed that among people hospitalized for the coronavirus, those with high levels of a protein called troponin — a sign of heart muscle damage — had a 61% death rate compared to a 9% death rate in people with normal troponin levels, regardless of underlying cardiovascular problems.
“Troponin gets elevated in a subset of patients even without having a history of known cardiovascular diseases, and in these people, the risk of dying from the condition is much higher,” says Madjid, who was not involved in the study. “It looks like the cardiac injury is happening in both people with and without heart disease.”
Like most complications resulting from the coronavirus, the heart damage appears to be the result not of the virus itself but the immune response that follows. The inflammatory reaction the body produces to fight off the viral infection can spiral out of control and end up damaging other organ systems, including the heart.
Again, old age and underlying health problems increase someone’s risk of this so-called cytokine storm from happening, and an already stressed heart because of obesity, diabetes, or hypertension could make the resulting damage even worse.
Genes might be the reason for severe illness in otherwise healthy young adults
Although the vast majority of severe cases of Covid-19 are in elderly people and people with preexisting conditions, there are still some previously healthy young adults who will be hospitalized and die from the infection.
Some scientists are turning to genetics to try to answer why. Could there be a gene variant that would otherwise have gone undetected that alters someone’s inflammatory immune response or their susceptibility to heart and lung damage?
“The hypothesis that we test is that they carry inborn errors of immunity — that is, that they carry single gene lesions that make them vulnerable to this particular virus, whether they encounter the virus at 5 years of age or 20 or 45.”
Jean-Laurent Casanova, MD, PhD, a professor at the Rockefeller University who runs the laboratory of human genetics of infectious diseases, is trying to answer this question by looking for gene variants specifically in young adults under the age of 50 with no underlying health conditions who fall extremely ill from the novel coronavirus.
“In these patients, the hypothesis that we test is that they carry inborn errors of immunity — that is, that they carry single gene lesions that make them vulnerable to this particular virus, whether they encounter the virus at five years of age or 20 or 45,” Casanova says. “It’s the encounter with the virus that reveals the phenotype which is encrypted in the genome.”
Casanova has done this work in the past for influenza, showing that variants in three genes that are involved in the body’s immune response were altered in people who developed severe complications from the virus. Now, he and collaborators from around the world are teaming up to look for other variants that might play a role in severe coronavirus infections. If they are successful, their findings could help guide drug development and vaccination priorities, not to mention answer important questions about the virus.
“If we crack the problem in a few patients — that is, if we understand some genetic cases — what’s great is that it illuminates the pathogenesis possibly even in nongenetic cases,” Casanova says.
There’s still a shortage of data, not to mention time to analyze it, when it comes to the novel coronavirus. And as scientists and public health officials learn more about the virus and the scope of the infection, some of these numbers, statistics, and best practices are bound to keep changing. But a clear picture that is emerging — and one that’s true for the vast majority of diseases — is that no one is immune to the virus, and good cardiovascular health and treating obesity pay off no matter how old someone is.
By Dana G Smith