- China confirmed the existence of the novel coronavirus nearly five months ago. The virus has since infected more than 5 million people globally.
- Scientific knowledge of the virus has evolved significantly: The latest research suggests the first case of the coronavirus appeared in November, disproves the theory that the virus came from snakes, and shows how the virus primarily spreads via droplets.
- Here are 18 of the biggest things that doctors, scientists, and public-health experts have come to realize about the virus.
- Visit Business Insider's homepage for more stories.
Since the novel coronavirus was first identified nearly five months ago, the world has come a long way in understanding how the virus spreads and attacks the body.
Over 5 million people globally have contracted COVID-19, the disease caused by the virus, and there are nearly 3 million active cases.
However, ongoing research has revealed that many of our best original assumptions about the virus weren't fully accurate — or in some cases misguided.
China confirmed the first case of a mysterious pneumonia-like illness at the end of December, for example, but reporting later suggested it likely started spreading it there in mid-November. The symptoms of COVID-19 also turned out to be far more expansive and peculiar than anyone initially realized. Even our knowledge of how the virus gets transmitted has evolved.
Here are 18 ways our understanding of the virus has changed over the course of the pandemic.
The first cluster of infections in Wuhan were reported in late December. However, the South China Morning Post reported that "patient zero" likely got sick in mid-November.
China reported the outbreak of a new coronavirus to the World Health Organization on December 31.
But according to Chinese government data obtained by the South China Morning Post, the first case emerged on November 17.
The identity of the person has not been confirmed, but it might have been a 55-year-old from the Hubei province (where Wuhan is located), the Post wrote.
More research has revealed that the virus likely jumped from a bat to humans through an intermediary animal.
The virus that caused the SARS coronavirus outbreak, which killed 774 people in the early 2000s, jumped from bats to civet cats to people.
Researchers have considered snakes or pangolins — an endangered, anteater-like mammal — as possible intermediary species for the new coronavirus but now don't believe that it was either of them.
By January, researchers understood that human-to-human transmission was possible. They now know the primary mode of transmission is via respiratory droplets.
Social-distancing rules suggest people stay 6 feet apart because coughing, talking, eating, or even sneezing can spread droplets up to that distance.
Newer studies suggest the virus can be aerosolized in certain situations, such as during intubation in hospitals, and travel as much as 13 feet.
Scientists confirmed that live virus particles can be found in infected patients' poop. and semen.
Researchers at the Chinese Center for Disease Control and Prevention detected viable virus particles in coronavirus patients' feces in March. The authors of the study wrote that "stool samples may contaminate hands, food, water, etc.," then cause infection if the particles enter a person's mouth, nose, or eyes.
Another team of Chinese researchers also discovered coronavirus particles in the semen of 16% of male patients studied, raising questions of sexual transmission. The virus was present in semen from both patients who had active infections and those who had recovered.
Scientists initially did not know how long the virus could survive on different types of materials. Recent studies have pinned down how long it remains viable on common surfaces.
Temperature and humidity also affect the survival of the viral particles.
A study found a correlation between the virus' lifespan and the surrounding temperature. At 4 degrees Celsius (39 degrees Fahrenheit), the virus lasted up to two weeks in a test tube. When the temperature was turned up to 37 degrees Celsius (99 degrees Fahrenheit), its lifespan dropped to one day.
At first, only people with telltale symptoms were being tested. But research has confirmed that people can test positive without feeling ill, and these asymptomatic carriers can spread the virus.
Between 25% and 50% of people who get the coronavirus may show no symptoms, according to Anthony Fauci, director of the National Institute of Allergy and Infectious Disease.
Some patients report gastrointestinal symptoms and other less frequent symptoms, which are increasingly well documented.
Almost half of COVID-19 patients in a one study experienced nausea, vomiting, or diarrhea. Other symptoms that occur at lower incidences include fatigue, body aches, and headaches.
Clinicians also now understand the typical progression of symptoms: The infection often lasts for about 17 days.
On average, a patient's symptoms start about five days after exposure to the virus. Nearly 98% of patients develop symptoms within 11.5 days, though about 1% start showing symptoms after 14 days.
Symptoms such as fever and coughing usually occur at the beginning of the infection. In severe cases, around day five, symptoms start to worsen and patients have difficulty breathing. By day eight, patients with severe cases will have most likely developed shortness of breath, pneumonia, or acute respiratory distress syndrome.
In some cases, symptoms can persist for over a month.
For some patients, mostly those with severe or critical cases, recovery can last up to six weeks, according to the WHO.
As the pandemic has progressed, two common sets of risk factors have become well known: age and underlying health conditions.
Those over age 50 face the highest risk of mortality. Data from around the world has also revealed which pre-existing conditions make patients more vulnerable to the disease: high blood pressure, obesity, diabetes, and heart disease.
Doctors have also begun to narrow in on a few factors that might explain why some cases get more severe than others.
New studies suggest that some level of coronavirus severity might be determined by your genes.
Different people's cells have different amounts of a type of receptor called ACE2, which is what the coronavirus binds to in order to invade cells. It can be found on the surface of cells throughout the body, including in our guts, lungs, hearts, and noses. Emerging research suggests that having more of these receptors is correlated with higher risk of severe coronavirus infection.
Another factor that researchers are realizing plays a role in severe cases is an aggressive immune response known as a "cytokine storm."
This response, known as a "cytokine storm," can lead to ARDS, a life-threatening lung injury, in coronavirus patients. For doctors treating coronavirus patients, knowing when to block a cytokine storm could be critical to preventing death.
It was initially assumed that the bodies of people who died from COVID-19 might spread the disease. This effect was documented in April.
A letter written by two scientists in Thailand shored up evidence for that risk in mid-April: It described the first suspected case of the illness spreading from the body of a person who died of COVID-19 to a forensic examiner.
As the pandemic continues, countries are still figuring out how to effectively fight the virus. When Wuhan issued a city-wide quarantine, it was an unprecedented step.
About one-third of humanity has come under some form of lockdown during the pandemic.
Overwhelming evidence suggests that these restrictions help contain coronavirus outbreaks and prevent additional deaths by reducing transmission.
Aria Bendix, Bill Bostock, Dave Mosher, and Aylin Woodward contributed reporting.
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