Illustration: Sarah Grillo/Axios

The novel coronavirus' characteristics are slowly becoming clearer — it's quite contagious possibly before symptoms show and is more deadly if you are over 60 and/or have underlying conditions. But, a lot remains fuzzy.

Why it matters: The threat of a pandemic has "become very real" but can "still be contained," the World Health Organization said Monday. Knowing how the virus spreads and why some experience mild — and others severe — symptoms is key to bringing this global outbreak to a halt.

The big picture

Since Chinese health officials first reported the "mysterious pneumonia outbreak" Dec. 31, the coronavirus has spread from its epicenter in Wuhan to over 100 countries and territories, infecting over 114,000 and killing more than 4,000 people.

  • China's rate of new cases has slowed dramatically and the WHO reported Monday that 70% of cases in the country have recovered.
  • In the U.S., there's been a growing number of confirmed cases (now at 755) and 26 deaths. But there's likely to be a large increase in confirmed cases as more testing finally becomes available.
What's happening

U.S. health officials are recommending cities prepare for mitigation, and people start practicing social distancing and avoiding large gatherings. This particularly applies to those over 60 and/or with underlying health conditions like heart, lung and kidney diseases.

What we know

The "clinical presentation is becoming a lot clearer," Emory University School of Medicine's Carlos del Rio told Axios. The largest data source is China's 44,672 patients but South Korea and Italy — two other hard-hit countries — have also started releasing data.

  • Symptoms: People with COVID-19 tend to have a fever, a dry cough and shortness of breath. 80% have mild/moderate symptoms including mild pneumonia, per WHO. 14% have more severe complications like severe pneumonia, and 6% are critical with respiratory failure, septic shock, and/or multiple organ failure.
  • Complications: Per Bloomberg, there's a "tipping point" when the virus travels to the lower respiratory tract where complications become worse.
  • Age matters: "Once you're 60 and older, the mortality rate starts getting up there," del Rio said. One reason, he says, could be that at that age "pulmonary reserve capacity is lower." Over 80 years old, the mortality rate reaches above 21%, WHO said Monday.
  • Health matters: WHO said Monday that initial data indicates the mortality rate for people with cardiovascular disease is 13%, diabetes 9%, chronic respiratory disease 8%, and undergoing cancer treatments at 5%.
  • The incubation period: The average incubation is 5 or 6 days, but can vary. Quarantine is 14 days.
  • Other indications: Young children and teenagers do not often experience severe complications and few under age 9 have confirmed cases. Men have a slightly higher risk of infection than women.
  • How the virus is transmitted: Droplets of SARS-CoV-2 can travel roughly 3 feet in the air before dropping to surfaces, but it is recommended to stay 6 feet from a person with COVID-19. (It is unknown how long it remains actively transmissible on surfaces.)
  • How the virus infects cells: A key protein structure in SARS-CoV-2 has been mapped, adding to info on how it may bind its human receptor at the surface of a cell — steps that could lead to vaccines or therapies.
What we still don't know

Fatality rate: As NIAID director Anthony Fauci told Axios last month, it's impossible to determine this when "both the denominator and numerator [of cases] are unknown."

  • WHO said March 3 their estimate was 3.4%, based on global data at that time.
  • Italy and South Korea — with the largest outbreaks outside China — are reporting different results. South Korea, which has been aggressively testing, reported a 0.6% death rate in early March. Italy — with the largest EU population of older adults — reported a 5% death rate on Sunday.
  • It's "very likely" there's a 2%–3.5% mortality rate, Lokesh Sharma of Yale School of Medicine, told Axios.

Contagiousness: One person is likely to infect about two to three. "We know it's very contagious, which makes it difficult to control," Sharma said.

  • But, why children appear to be protected or how many are asymptomatic and unreported is unknown, he added.
  • It's has been found in blood and stool, but remains unknown if those are routes of transmission, del Rio said.

Reinfection: A small number of reports say some people are getting reinfected, which could mean the virus doesn't prompt an effective immune response, similar to hepatitis C, del Rio said.

  • But, Jennifer Nuzzo, a senior scholar at Johns Hopkins Center for Health Security, told Axios it's more likely the original infection is persisting.

Future trajectory: The virus appears to be mutating slower than the flu, at one to two mutations per month, and we don't know if it will be affected by seasonal weather and behaviors.

The bottom line

Even if this doesn't reach a pandemic status, "this is a good opportunity for all of us to learn a lesson on effectively finding ways to control this kind of thing," Sharma said.

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