The new coronavirus that has already killed more people than the 2003 SARS epidemic appears to be sparing one population group: kids.
Of the more than 43,100 people it's infected since Dec. 31, World Health Organization officials say the majority are over 40 years old and it's hitting those with underlying health conditions and the elderly particularly hard.
"Increasing age increases the risk for death," Dr. Maria Van Kerkhove, head of WHO's emerging diseases and zoonosis unit, said Thursday at a news conference at the agency's headquarters in Geneva. "It appears even over 80 is the highest risk factor."
Fortunately for many worried parents, there appear to be few confirmed cases of the virus among children so far. Officials caution that the virus is so new, there is still a lot that they don't know about it and the data they are seeing today will likely look different a month from now.
About 80% of people who died from the virus in China were over the age of 60, and 75% had pre-existing conditions such as heart disease or diabetes, according to a recent report from China's National Health Commission. A small study published Jan 30 in the peer-reviewed medical journal The Lancet found that the average age of coronavirus patients was roughly 55 years old. The study looked at 99 patients at Jinyintan Hospital in Wuhan, China, from Jan. 1 to Jan. 20.
Last week, Singapore confirmed a case in a 6-month-old baby whose parents were also both infected, and an infant in China was born Feb. 2 with the virus. The baby's mother also tested positive. But infections in children appear to rare for now, according to a Feb. 5 study in the peer-reviewed Journal of the American Medical Association.
Symptoms can include a sore throat, runny nose, fever or pneumonia and can progress to multi-organ failure or even death in some cases, world health officials say.
Some infectious disease specialists and scientists say older adults may be more vulnerable to the virus, which has been named COVID-19, due to their weaker immune systems.
With age, immune systems weaken, leaving the elderly at an especially higher risk of developing serious complications from a respiratory illness, public health officials say.
"It's usually the very old, sometimes the very young and certainly people with other medical conditions who typically have more severe manifestations," said Isaac Bogoch, an infectious disease specialist and professor at the University of Toronto.
The apparent lack of children among confirmed coronavirus cases could also be because they are getting infected but developing more mild symptoms and aren't being reported to local authorities, according to Marc Lipsitch, a professor of epidemiology at the Harvard School of Public Health. World health officials say they are working to improve surveillance of the disease and expect more mild cases to be reported. It could be a while before we have a clear picture on cases, Lipsitch said.
"The data is coming out in so many places and so many forms," he said in a recent interview.
The differences in symptoms among different age groups are seen in other respiratory illnesses as well. The seasonal flu, which infects millions in the U.S. each year, can usually be more severe in adults than children.
Thousands of children are hospitalized each year from the flu, but death is rare, according to the Centers for Disease Control and Prevention. However, between 50% and 70% of flu-related hospitalizations in the U.S. occur in people 65 years and older, and between 70% and 85% of deaths occur in the same age group, the CDC says.
The lack of confirmed cases in children was also seen in another coronavirus. During the 2003 outbreak of SARS, which sickened 8,098 people and killed about 800 over nine months, the vast majority of cases infected older adults, according to WHO data. The case-fatality ratio for people age 24 or younger was less than 1%, according to WHO.
Even if children are only developing mild symptoms, Lipsitch said scientists still need to know whether they can still infect others at high rates. "This is a key uncertainty that needs to be resolved," he said.
When asked whether mild cases are transmitting the virus, Kerkhove of WHO said Thursday that more studies need to be conducted.
"We need to look at mild individuals all the way to severe individuals," Kerkhove said. "That systematic data collection and that sampling of mild cases, as well as severe cases, is something that is really urgently required for us to get a clear handle on this."
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Correction: Dr. Maria Van Kerkhove is head of WHO's emerging diseases and zoonosis unit. An earlier version misspelled her name.