- Nearly 4 months ago, China confirmed the existence of the novel coronavirus. The virus has now infected more than 2.4 million people globally.
- Scientific knowledge of the virus has since evolved, including understanding of how it infects people and spreads among populations.
- The latest research suggests the first case of the coronavirus appeared in November, has the theory that the virus came from snakes, and shown the virus spreads via droplets.
- Here are 11 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 coronavirus2020欧洲杯夺冠热门 was first identified nearly 4 months ago, the world has come a long way in understanding how the virus infects people and how it spreads among populations.
Over 2.43 million people around the world have contracted COVID-19, the disease caused by the virus, and there are more than 1.6 million active cases.
However, ongoing research on and about these patients has revealed that many of our best original assumptions about the virus weren't fully accurate — or in some cases misguided.
After China confirmed the first case of the mysterious "pneumonia-like" illness at the end of December, for example, it turned out someone else likely started spreading it there in November. Symptoms of COVID-19 also turned out to be far more expansive and peculiar than anyone initially realized. Even our understanding of how the virus transmits itself from one person to the next has changed.
Here are all of the ways that what we know about the virus has changed over the course of the pandemic.
The first infection appeared to happen in Wuhan in December. However, China said 'patient zero' likely appeared in mid-November.
China officially confirmed the first case of the new coronavirus on December 31.
2020欧洲杯夺冠热门But according to Chinese government data , the first case of the novel coronavirus emerged on November 17.
The identity of the person has not been confirmed, but it appears to be a 55-year-old from the Hubei province, the Post wrote.
Theories that the virus arrived in the US during the fall, however, are .
More research has revealed that the virus likely jumped from a bat to humans through an intermediary animal, such as a pangolin or a civet cat.
The virus that caused the SARS coronavirus outbreak2020欧洲杯夺冠热门, which killed 774 people in the early 2000s, jumped from bats to civets to people.
Pangolins2020欧洲杯夺冠热门 — an endangered, anteater-like mammal — are another candidate for intermediary species.
2020欧洲杯夺冠热门A group of researchers from South China Agricultural University found that samples from coronavirus patients were a 99% match to , according to China's official Xinhua news agency. However, their research hasn't been published or confirmed by other experts.
By January, researchers firmly understood human-to-human transmission was possible. Now it's known the primary mode of transmission is via droplets, which can sometimes spread through the air.
Social distancing rules specify 6 feet because coughing, eating, or even sneezing can spread droplets up to that length.
Newer studies suggest the virus can be aerosolized in certain situations, such as hospital intubation, and travel as much as 13 feet.
Scientists initially did not know how the virus fared on different types of materials. Recent studies have pinned down how long it remains viable on common surfaces and in various conditions.
Temperature and humidity also affect the survival of the viral particles.
2020欧洲杯夺冠热门A new found a similar link 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 to help curb the spread of COVID-19. But testing of those in close contact with patients who didn't have symptoms also carried the virus.
They also found out that these asymptomatic carriers could still spread the virus.
Moreover, asymptomatic carriers may represent the vast majority of carriers. An early and as-yet unpublished study of 3,300 people living in Santa Clara, California, suggests the infection rate is 50 to 85 times as high as the number of confirmed cases.
Initially, it was difficult to know what symptoms were telltale signs of an infection. Larger case studies of patients now show that the type and severity of disease symptoms spans an impressive range.
The severity of COVID-19 cases is a spectrum. Cases are categorized as "asymptomatic," "mild," "severe," or "critical." "Mild" is something of a misnomer, though, because it clinically refers to patients who don't need to be hospitalized.
Patients with severe cases are more likely to have shortness of breath, difficulty breathing, and fluid in their lungs. Usually, they'll require care from a medical professional. (Mild cases can develop into severe cases if infections worsen.)
2020欧洲杯夺冠热门Critical cases will need medical care from a hospital, often in the Intensive Care Unit. These patients can exhibit respiratory failure, septic shock, and organ failure. And of course some people don't seem to exhibit any symptoms.
COVID-19 patients might experience different symptoms as well. Fever presents in 99% of COVID-19 patients, according to a study of nearly 140 patients at the Zhongnan Hospital of Wuhan University. So almost all mild cases involve a high temperature.
A cough occurs in between 60 and 80% of COVID-19 patients, arriving in tandem with a fever at the onset of the disease. It's usually a dry cough.
A sizable number of patients reported gastrointestinal symptoms, despite COVID-19 taxing the respiratory system. These and other less frequent symptoms are now well-documented.
Almost half of COVID-19 patients in a recent study experienced nausea, vomiting, or diarrhea.
One patient with abdominal symptoms was initially placed in a surgical ward in a hospital in China because doctors didn't suspect COVID-19. The patient then transmitted the virus to at least 10 healthcare workers and four other patients.
2020欧洲杯夺冠热门Other symptoms that occur at lower incidences include shortness of breath, fatigue, body aches, headaches, and gastrointestinal issues.
Also, clinicians didn't fully understand the most common courses for the illness. Now they know the virus follows a pattern of symptoms spanning about 17 days.
On average, a patient's symptoms start about five days after exposure to the virus, according to a published Monday in the journal Annals of Internal Medicine. 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.
2020欧洲杯夺冠热门The infection usually lasts around 14 days in patients with mild cases, but can last for two and half to three weeks in patients with more severe cases.
Some people were inexplicably and lethally affected by COVID-19 early on. As the pandemic progressed, certain age and other risk factors for the disease emerged.
It's now widely documented that those over the age of 50 face the highest risk of mortality. But that is likely due to an accumulation of risk factors.
2020欧洲杯夺冠热门Data from many countries' centers for disease control have shown which pre-existing conditions make patients more vulnerable to the disease. Patients with high blood pressure, besties, diabetes, and heart disease usually develop more severe cases of coronavirus.
It was assumed that the bodies of people who died from COVID-19 might spread the disease. However, it was only in April that this effect was documented.
Funeral directors and other "deathcare" workers have assumed the bodies they're paid to handle2020欧洲杯夺冠热门 might spread the novel coronavirus, but many have struggled to obtain personal protective equipment.
A written to an academic journal by two scientists in Thailand, however, shored up some evidence for that risk in mid-April: the first suspected case of the illness spreading from the body of a person who died from COVID-19 spreading to a forensic examiner.
And as the pandemic continues, countries are still figuring out how to effectively fight the virus. When Wuhan issued a city-wide quarantine and locked down its 11 million residents, it was an unprecedented step. Now, about one-third of humanity is under some form of lockdown.
Aria Bendix, Bill Bostock, Dave Mosher, and Aylin Woodward contributed reporting.
Do you have a personal experience with the coronavirus you'd like to share? Or a tip on how your town or community is handling the pandemic? Please email firstname.lastname@example.org and tell us your story.
Get the latest coronavirus business & economic impact analysis from Business Insider Intelligence on how COVID-19 is affecting industries.