18 critical things we've learned about the coronavirus since the earliest reported cases in China

coronavirus covid 19 healthcare worker doctor nurse sitting sits face mask scrubs central park new york city nyc 2020 03 30T000000Z_2108372485_RC2NUF9VY5KU_RTRMADP_3_HEALTH CORONAVIRUS USA NEW YORK.JPG coronavirus covid 19 healthcare worker doctor nurse sitting sits face mask scrubs central park new york city nyc 2020 03 30T000000Z_2108372485_RC2NUF9VY5KU_RTRMADP_3_HEALTH CORONAVIRUS USA NEW YORK.JPG
Healthcare worker sits on a bench near Central Park in the Manhattan borough of New York City, on March 30, 2020.
Jeenah Moon/Reuters
  • 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.

wuhan map
The location of Wuhan, a city in China's Hubei province.
Ruobing Su/Business Insider

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.

Originally, the virus' origin was linked to the Huanan Wholesale Seafood Market in Wuhan, where it was thought to have jumped from an animal to a person. That no longer appears to be the case.

china wet market
A Chinese wet market.
Felix Wong/South China Morning Post/Getty

At some wet markets, meat, poultry, and seafood are sold alongside live animals. The Huanan Seafood Wholesale Market was closed on January 1, the day after China confirmed the first case of the novel coronavirus.

Wuhan authorities banned the trade of live animals at all wet markets there soon after. In February, China announced a national ban on the buying, selling, and transportation of wild animals in markets, restaurants, and online marketplaces across the country.

However, a group of Chinese scientists published a report at the end of January that found that out of the first 41 cases of the virus in Wuhan, only 13 were connected to the wet market — indicating that it was not the outbreak's initial origin site.

Now it seems that the market might have been the site of a super-spreading event by an infected person.

More research has revealed that the virus likely jumped from a bat to humans through an intermediary animal.

Civet Cat Coffee
AP

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.

Coronavirus social distancing meeting
President Donald J. Trump, joined by Vice President Mike Pence, meets with tourism industry executives to discuss the health care and economic responses to the coronavirus (COVID-19) outbreak, Tuesday, March 17, 2020
D. Myles Cullen/White House

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.

sex health sexual genitals female male anatomy peach crotch orgasm pleasure same sex reproduction penis testicles anal vagina vibrator toy sperm uterus ovaries condom safe sex cox 126 130.jpg
Crystal Cox/Business Insider

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.

how long covid 19 can live on common surfaces
Shayanne Gal/Business Insider

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.

coronavirus test uk
Getty

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.

Initially, it was difficult to know which symptoms were signs of a coronavirus infection. Larger case studies of patients now show that the type and severity of symptoms ranges significantly.

coronavirus symptoms april 2020 update
Samantha Lee/Business Insider

COVID-19 cases are often categorized as "asymptomatic," "mild," "severe," or "critical." "Mild" refers to patients who don't need to be hospitalized. (Mild cases can develop into severe cases if infections worsen.)

Patients with severe cases are more likely to experience difficulty breathing and have fluid in their lungs. Usually, they require care from a medical professional. Critical cases need medical care at a hospital, often in the intensive-care unit. These patients can face respiratory failure, septic shock, and organ failure. 

The most common symptom across all cases is fever: A February report from the WHO found that out of nearly 56,000 coronavirus patients studied in China, about 88% developed a fever. The report found that 68% of patients developed a dry cough.

 

Some patients report gastrointestinal symptoms and other less frequent symptoms, which are increasingly well documented.

hospital clinicians coronavirus
Hospital clinicians get into their protective equipment before testing patients for the coronavirus, Covid-19 at Newton-Wellesley Hospital in Newton, Massachusetts on March 18, 2020, as the hospital has set up three tents in the parking garage where patients who have been pre-screened can show up for testing.
Joseph Prezioso/Getty Images

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.

A growing body of evidence suggests that coronavirus patients,?including young people, could suffer from strokes as a result of blood clots.

Stroke
create jobs 51/Shutterstock

"The number of clotting problems I'm seeing in the ICU, all related to COVID-19, is unprecedented," Dr. Jeffrey Laurence, a hematologist at Weill Cornell Medicine in New York City, told CNN in April. "Blood clotting problems appear to be widespread in severe COVID."

Doctors think the strokes are likely tied to these clots.

Scientists are still figuring out how the coronavirus impacts a person's nervous system more broadly. A study of 214 patients in Wuhan found that more than a third had neurological symptoms — 25% experienced dizziness, headache, confusion, delirium, seizure, or impaired balance or coordination. This was most common among people with severe infections. Less than 6% of the patients experienced a stroke. 

 

A rare, serious inflammatory reaction in children has also been linked to the virus — doctors are calling it "multisystem inflammatory syndrome in children" (MIS-C).

children coronavirus
A girl wears gloves and mask before going to the park after children under 14 years are allowed to leave their homes in Turkey on May 13, 2020.
Aykut Unlupinar/Anadolu Agency/Getty Images

Doctors in Europe, the UK, and the US have reported seeing children with high fever and inflammation. The illness, which can be deadly, appears to be similar to Kawasaki disease, which inflames the walls of the arteries and typically affects just one in 10,000 children.

Clinicians also now understand the typical progression of symptoms: The infection often lasts for about 17 days.

3D print of a SARS-CoV-2
3D print of a SARS-CoV-2—also known as 2019-nCoV, the virus that causes COVID-19—virus particle. The virus surface (blue) is covered with spike proteins (red) that enable the virus to enter and infect human cells.
NIH

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.

coronavirus patient
Halfpoint/Shutterstock

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.

covid net preexisting conditions 4 8 20
Andy Kiersz/Insider

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.

coronavirus patient covid19 sick hospital intensive care
A medical staff member is seen next to a patient suffering from COVID-19 in the intensive-care unit at the Circolo hospital in Varese, Italy, April 9, 2020.
Flavio Lo Scalzo/Reuters

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."

coronvirus severe cases france
French SMUR rescue team wearing protective suits carry a patient at Strasbourg University hospital as France faces an aggressive progression of the coronavirus disease (COVID-19), March 16, 2020.
Christian Hartmann/Reuters

Some new research shows that this aggressive immune reaction prompts white blood cells to attack healthy lung tissue, which can make a coronavirus cases to go from mild to severe.

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.

Makeshift morgue NYC
An Air Force member exits a tent builded as makeshift morgue outside of Bellevue Hospital on March 25, 2020 in New York City.
Eduardo Munoz Alvarez/Getty Images

Funeral directors and other "deathcare" workers have assumed the bodies they're paid to handle might spread the novel coronavirus, but many have struggled to obtain personal protective equipment.

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.

FILE PHOTO: A man walks his dog in Paris during a lockdown imposed to slow the spread of the coronavirus disease (COVID-19) in France, April 7, 2020. REUTERS/Gonzalo Fuentes
Paris during a lockdown imposed to slow the spread of the coronavirus disease (COVID-19)
Reuters

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.

Loading Something is loading.

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 covidtips@businessinsider.com and tell us your story.

Get the latest coronavirus business & economic impact analysis from Business Insider Intelligence on how COVID-19 is affecting industries.

More: coronavirus COVID-19 Symptoms pandemics
Chevron icon It indicates an expandable section or menu, or sometimes previous / next navigation options.