Covid-19: What we now know about the disease caused by the novel coronavirus

Each day new information comes out about the deadly novel coronavirus and Covid-19, the disease it causes, making it difficult to keep up with all that science has learned.

Here’s a wrap-up of what has changed since the pandemic began and what you need to know now to keep you and your family safe.

What are the symptoms of Covid-19?

Fever, cough and shortness of breath: The big three are still the most common symptoms, but the list has grown over the months. We now know many common cold and flu symptoms can also play a role, such as a sore throat, headache, body and muscle aches, chills and shivers, a snotty or congested nose, intense fatigue (which can last longer than the illness), diarrhea, nausea and vomiting.

New, bizarre symptoms: Skin rashes and “Covid-toes,” where the toes become red and swollen from tiny blood clots, are some of the newer symptoms that may be early warning signs of Covid-19.

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More early signals include pink eye (a highly contagious eye condition also known as conjunctivitis), anosmia (a loss of smell that can also lead to a loss of taste), and a sudden, new onset of confusion, even to the point of delirium.

Emergency symptoms: An inability to wake or stay awake, chest pain or pressure, new mental confusion or delirium, blue-tinged lips or any sudden or severe breathing problems can all signal an emergency, warns the US Centers for Disease Control and Prevention, so call 911 immediately.

Read more: Covid-19 symptoms – what we know now and what to do

Who is most at risk?

Everyone: The virus can infect anyone, even babies in the womb. It’s how your body responds to the virus that is the key question. The answer appears to be a complex interplay between viral load – how much virus you were exposed to – and your age and health.

At first, the CDC said it was seniors over 65, especially if they had an underling health condition, who were at highest risk of serious illness and death. But that’s no longer true. People in their 20s, 30s and 40s – even some children – have collapsed and died from Covid-19 – some when their immune systems overreacted to the virus, in what is called a “cytokine storm.”

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Others have been “knocked out on their back and brought to their knees pretty quick,” by Covid-19, said White House adviser Dr. Anthony Fauci in an interview Thursday with Facebook CEO Mark Zuckerberg. Fauci is the top infectious diseases expert in the US.

“There are many, many young people who get infected. They get sick. They feel horrible for weeks and weeks,” Fauci said, adding that he has noticed young people experiencing something similar to chronic fatigue syndrome after recovering from the virus.

“Even when they clear the virus, and they test negative – they don’t have any virus – they can feel out of sorts for weeks and weeks.”

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Age and health are key: Science now knows that anyone – at any age – with at least one chronic health condition is at greater danger from Covid-19. The risk rises with increasing age, the number of underlying medical conditions you have and whether or not you are obese (body mass index or BMI over 30).

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That’s a lot of people at risk: Just in America, more than 40% of the population are considered obese, according to the CDC, while some 60% of American adults have at least one chronic medical condition.

High-risk medical conditions: That list is long and growing. Currently, it includes diabetes, chronic lung disease or asthma, cardiovascular disease, cancer (or are undergoing chemotherapy), organ transplants, sickle cell anemia, kidney disease with dialysis, poorly controlled HIV infection, obesity and any autoimmune disorder.

Pregnancy raises risk: Early in the pandemic, expecting mothers and their fetus or newborn were not considered at high risk.

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That too has changed, as doctors have found the virus can cross the placenta to infect the fetus. We now know that women who are pregnant are 50% more likely to end up in the intensive care unit and 70% more likely to receive mechanical ventilation.

Nursing home, veteran’s home, long-term care facilities: Facilities which house the older and more infirm in society are typically more crowded, with fewer staff to care for the needs of inhabitants individually. In addition, adults in these facilities are older, weaker, and likely to have multiple health issues and frail immune systems.

The toll has been devastating: In the US, nursing home residents comprised 35%? of the more than 87,000 coronavirus deaths ?recorded as of May 15. In Belgium, France, Ireland, Canada and Norway it was over 50%.

Read more: Tragic Covid-19 outbreak at Massachusetts veterans home

How does the novel coronavirus spread?

Person-to-person: The vast majority of transmission of SARS Covid-2, the novel coronavirus’s scientific name, is person-to-person. The virus predominately spreads via respiratory droplets sprayed into the air as an infected person coughs, sneezes, sings or talks. For the most part, those droplets can travel in about a six-foot radius from the infected person.

Watch:Why six-feet social distancing works

Objects: Heavier droplets will fall more quickly to the ground, thus infecting surrounding objects with the virus, which can stay viable – to some degree – for days. While the virus does break down and become weaker as time goes on, studies have found traces of SARS Covid-2 after four hours on copper, 24 hours on cardboard, and two to three days on stainless steel and plastic.

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Despite that, it’shighly unlikely you’d get the novel coronavirus from your groceries and next to impossible to get it from food, experts say.

Read more: No need to wipe down groceries or take-out

Kissing, semen and feces: Because SARS Covid-2 is found in saliva, kissing can obviously transmit the virus. It’s also been found in semen, but it isn’t clear if it virus is viral enough to be infectious. While it’s unlikely that it can be transmitted during vaginal, anal or oral sex, those with active infections may consider abstaining or using a condom.

It has also been found in feces. A good reminder to always close the lid on your toilet before you flush, wash hands with soap often and for at least 20 seconds, and frequently clean and disinfect common areas of your home.

Floating in the air? Recent studies show smaller respiratory droplets that sputter out of an infected person’s mouth can more quickly dry out, this possibly allowing the virus to become aerosolized and float away into the air. In extremely large, well ventilated areas and outdoors, air circulation will dilute the particles, thus greatly lowering any risk. That changes inside smaller, enclosed spaces, such as inside restaurants, offices, shops, cars, public transport and the like, experts say.

Read more: Can an A/C filter protect you from coronavirus?

When and how long are you contagious?

Incubation period: Science now knows there is a lengthy (and somewhat uncertain) incubation period after exposure to Covid-19. Typically, symptoms will appear within five to seven days, but they can show up as early as two days after exposure and as late as 14 days – with a rare few taking even longer.

Contagious and don’t know it: Like many viruses, the novel coronavirus is contagious well before it makes itself known. Researchers estimate anyone infected can spread the virus to others 2 to 3 days before symptoms start, and may be the most contagious in the one to two days before they feel sick.

Iris from Vienna puts on her homemade nasal and mouth protection masks on during the novel coronavirus Covid 19 pandemic in Vienna on April 7, 2020. - Austria could start loosening its coronavirus blocking measures next week, said Chancellor Sebastian Kurz on April 6 2020, but warned citizens that they must abide by the rules of social distancing. (Photo by ALEX HALADA / AFP) (Photo by ALEX HALADA/AFP via Getty Images)

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The US Centers for Disease Control and Prevention estimates 40% of coronavirus transmission happens when people are presymptomatic – before they feel sick. If they ever feel sick, that is.

No symptoms: One of the deadliest discoveries researchers have made is that the virus can cause no symptoms or possibly such mild symptoms that a person has no idea they have the disease.

“Evidence shows that 25% to 45% of infected people likely don’t have symptoms,” Fauci told ABC’s “Good Morning America” in mid-June.

These asymptomatic – and presymptomatic – people go about their lives spreading the disease without knowing it. That’s a key reason wearing a mask when in public is so important.

Read more: The right (and wrong) way to wear a mask

No longer contagious: The CDC says that you can be around others when you meet these three milestones: You haven’t had a fever in 3 days AND your cough and shortness of breath have improved AND it’s been 10 days since your symptoms first appeared. If your immune system is compromised, however, you may need to extend that time table.

Hands close up woman wearing face mask. Studio shot masked woman staff putting mask on her face on grey background. Coronavirus or Covid-19 concept.

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If you tested positive for Covid-19 but never had symptoms, you can be around others 10 days after the test – as long as no symptoms appeared.

If you’ve been exposed to someone who tested positive, you need to stay home for a full 14 days, the CDC says.

Can you get Covid-19 more than once?

Scientists around the world have been hoping that being infected with SARS Covid-2 will produce powerful antibodies and immunity against any future exposure to the virus – much like having measles, mumps and chickenpox protects you from ever getting any of those diseases again. Recent non-peer reviewed studies show good and bad news.

Good news: It does appear that people develop antibodies after recovering from Covid-19 – some develop more than others, possibly due to the amount of virus they were exposed to and their body’s immune response.

Bad news: Unfortunately, at this time those antibodies don’t appear to last more than a month or two. That means SARS Covid-2 may behave like other, more common coronviruses circulating every year known to cause the common cold.

“Similar short-lived responses are seen against other human coronaviruses that predominantly cause only mild illness, meaning that we can be re-infected as time goes by and outbreaks can adopt seasonality,” said Stephen Griffins, associate professor in the University of Leeds School of Medicine in the United Kingdom, in a written statement.

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“With the more serious, sometimes fatal, outcomes of SARS-COV2, this is troubling indeed,” Griffins added.

It’s possible that lingering memory immune cells may recognize and battle the virus the next time it invades, thus possibly leading to a milder case of But there’s no way of knowing that right now, experts say.

Vaccine development impact: How this lack of immunity will affect many of the vaccines under development is also unclear. Will they produce enough of an antibody response to last?

“It suggests vaccines will need to be better at inducing high levels of longer-lasting antibodies than the natural infection or that doses may need to be repeated to maintain immunity,” said Dr. Mala Maini, a professor of viral immunology and consultant physician at the University College London, in a statement.

Read more: Promising results for one vaccine, but more research needed

How can I protect myself?

Prevention is the best defense: Mom taught you this as a child: Cough or sneeze into your elbow, wash your hands – properly, with soap and water while you sing “Happy Birthday” twice (or another of these songs) – and stay away from others who are sick.

Mom knew best, of course: Since you can’t really tell who is sick with Covid-19, you can add to her wisdom by wearing a mask every time you leave the house and engage with others. It may not be long before your city or state requires you to do so.

It’s not brain surgery: It’s a no brainer to stay six feet away from everyone else when you go out – that’s the social distancing golden rule. But other no-duhguidelines include:

And please – no bars. Besides the close quarters, all that alcohol lowers inhibitions and removes common sense – something we could all use more of right now.

Read more: All your coronavirus questions answered

CNN’s Jacqueline Howard, Holly Yan and Lauren Mascarenhas contributed to this report.