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More than 236,000 people have been infected with a new coronavirus that has spread widely from its origin in China over the past few months. Nearly 9,900 have already died. Our comprehensive guide for understanding and navigating this global public health threat is below.
This is a rapidly developing epidemic, and we will update this guide every day at 3pm EDT to keep you as prepared and informed as possible.
March 8: Initial publication of the document.March 9, 3pm ET: Added three new question-and-answer sections and updated case counts.March 10, 3pm ET: Added one new question-and-answer section and updated case counts.March 11, 3pm ET: Added a new section about claimed remedies and updated case counts.March 12, 3pm ET: Updated the sections on US cases and how SARS-CoV-2 spreads. Updated global case counts.March 13, 3pm ET: Updated the answers to “Should I avoid large gatherings and travel?” and “How does coronavirus transmission compare with flu?” Also updated global and US case counts.March 14, 3pm ET: Updated global and US case counts.March 15, 3pm ET: Updated global and US case counts.March 16, 3pm ET: Updated global and US case counts. Updated guide on what to keep in your medicine cabinet.March 17, 3pm ET: Updated global and US case counts.March 18, 3pm ET: Updated global and US case countsMarch 19, 3pm ET: Added new section on risks for pregnant women. Updated global and US case counts
Table of Contents

  • How worried should I be?
  • What is SARS-CoV-2?
  • Where did SARS-CoV-2 come from?
  • How did it start infecting people?
  • What happens when you’re infected with SARS-CoV-2?
  • What are the symptoms?
  • How severe is the infection?
  • Who is most at risk of getting critically ill and dying?
  • Are men more at risk?
  • Are children less at risk?
  • ⇒ ♦♦♦  Are pregnant women at high risk? [NEW, 3/19/2020] ♦♦♦
  • How long does COVID-19 last?
  • How many people die from the infection?
  • How does COVID-19 compare with seasonal flu in terms of symptoms and deaths?
  • How does SARS-CoV-2 spread? [Updated 3/12/2020]
  • How does coronavirus transmission compare with flu? [Update 3/13/2020]
  • How contagious is it? [New, 3/9/2020]
  • Can I get SARS-CoV-2 from my pet? Can I give it to my pet? [New, 3/9/2020]
  • If I get COVID-19, will I then be immune or could I get re-infected? [New, 3/9/2020]
  • How likely am I to get it in normal life?
  • What can I do to prevent spread and protect myself?
  • Should I get a flu vaccine?
  • When, if ever, should I buy or use a face mask?
  • Should I avoid large gatherings and travel? [Updated 3/13/2020]
  • What precautions should I take if I do travel?
  • Do quarantines, isolations, and social-distancing measures work to contain the virus? [New, 3/10/2020]
  • How should I prepare for the worst-case scenario?
  • Should I keep anything in my medicine cabinet for COVID-19? [Updated, 3/16/2020]
  • Can X home remedy or product prevent, treat, or cure COVID-19? [New, 3/11/2020]
  • Should I go to a doctor if I think I have COVID-19?
  • When should I seek emergency care?
  • Is the US healthcare system ready for this?
  • What are the problems with testing in the US?
  • ⇒ ♦♦♦ Current cases in the US [Updated, 3/19/2020]  ♦♦♦
  • What could happen if healthcare facilities become overwhelmed?
  • When will all of this be over in the US?
  • Will SARS-CoV-2 die down in the summer?
  • Will it become a seasonal infection?
  • What about treatments and vaccines?

How worried should I be?
You should be concerned and take this seriously. But you should not panic.
This is the mantra public health experts have adopted since the epidemic mushroomed in Januaryand its about as comforting as it is easy to accomplish. But its important that we all try.
This new coronavirusdubbed SARS-CoV-2is unquestionably dangerous. It causes a disease called COVID-19, which can be deadly, particularly for older people and those with underlying health conditions. While the death rate among infected people is unclear, even some current low estimates are seven-fold higher than the estimate for seasonal influenza.
And SARS-CoV-2 is here in the US, and it’s circulatingwe are only starting to determine where it is and how far it has spread. Problems with federal testing have delayed our ability to detect infections in travelers. And as we work to catch up, the virus has kept moving. It now appears to be spreading in several communities across the country. Its unclear if we will be able to get ahead of it and contain it; even if we can, it will take a lot of resources and effort to do it.
All that said, SARS-CoV-2 is not an existential threat. While it can be deadly, around 80 percent of cases are mild to moderate, and people recover within a week or two. Moreover, there are obvious, evidence-based actions we can take to protect ourselves, our loved ones, and our communities overall.
Now is not the time for panic, which will only get in the way of what you need to be doing. While its completely understandable to be worried, your best bet to getting through this unscathed is to channel that anxious energy into doing what you can to stop SARS-COV-2 from spreading.
And to do that, you first need to have the most complete, accurate information on the situation as you can. To that end, below is our best attempt to address all of the questions you might have about SARS-CoV-2, COVID-19, and the situation in the US.
Well start with where all of this startsthe virus itself.
What is SARS-CoV-2?
SARS-CoV-2 stands for severe acute respiratory syndrome coronavirus 2. As the name suggests, its a coronavirus and is related to the coronavirus that causes SARS (Severe Acute Respiratory Syndrome). Note: When SARS-CoV-2 was first identified it was provisionally dubbed 2019 novel coronavirus, or 2019-nCoV.
Coronaviruses are a large family of viruses that get their name from the halo of spiked proteins that adorn their outer surface, which resemble a crown (corona) under a microscope. As a family, they infect a wide range of animals, including humans.
With the discovery of SARS-CoV-2, there are now seven types of coronaviruses known to infect humans. Four regularly circulate in humans and mostly cause mild to moderate upper-respiratory tract infectionscommon colds, essentially.
The other three are coronaviruses that recently jumped from animal hosts to humans, resulting in more severe disease. These include SARS-CoV-2 as well as MERS-CoV, which causes Middle East Respiratory Syndrome (MERS), and SARS-CoV, which causes SARS.
In all three of these cases, the viruses are thought to have moved from batswhich have a large number of coronavirus strains circulatingto humans via an intermediate animal host. Researchers have linked SARS-CoV to viruses in bats, which may have moved to humans through masked palm civets and raccoon dogs sold for food in live-animal street markets in China. MERS is thought to have spread from bats to dromedary camels before jumping to humans.
Where did SARS-CoV-2 come from?
SARS-CoV-2 is related to coronaviruses in bats, but its intermediate animal host and route to humans are not yet clear. There has been plenty of speculation that the intermediate host could be pangolins, but that is not confirmed.
How did it start infecting people?
While the identity of SARS-CoV-2s intermediate host remains unknown, researchers suspect the mystery animal was present in a live animal market in Wuhan, Chinathe capital city of Chinas central Hubei Province and the epicenter of the outbreak. The market, which was later described in Chinese state media reports as filthy and messy, sold a wide range of seafood and live animals, some wild. Many of the initial SARS-CoV-2 infections were linked to the market; in fact, many early cases were in people who worked there.
Public health experts suspect that the untidiness of the market could have led to the virus spread. Such markets are notorious for helping to launch new infectious diseasesthey tend to cram humans together with a variety of live animals that have their own menageries of pathogens. Close quarters, meat preparation, and poor hygienic conditions all offer viruses an inordinate number of opportunities to recombine, mutate, and leap to new hosts, including humans
That said, a report in The Lancet describing 41 early cases in the outbreak indicates that the earliest identified person sickened with SARS-CoV-2 had no links to the market. As Ars has reported before, the case was in a man whose infection began causing symptoms on December 1, 2019. None of the mans family became ill, and he had no ties to any of the other cases in the outbreak.
The significance of this and the ultimate source of the outbreak remain unknown.
The market was shut down and sanitized by Chinese officials on January 1 as the outbreak began to pick up.
What happens when youre infected with SARS-CoV-2?
In people, SARS-CoV-2 causes a disease dubbed COVID-19 by the World Health Organization (WHO). As the US Centers for Disease Control and Prevention (CDC) points out, the CO stands for corona, VI for virus, and D for disease.
What are the symptoms?
COVID-19 is a disease with a range of symptoms and severities, and we are still learning about the full spectrum. So far, it seems to span from mild or potentially asymptomatic cases all the way to moderate pneumonia, severe pneumonia, respiratory distress, organ failure and, for some, death.
Many cases start out with fever, fatigue and mild respiratory symptoms, like a dry cough. Most cases dont get much worse, but some do progress into a serious illness.
According to data from nearly 56,000 laboratory-confirmed COVID-19 patients in China, the rundown of common symptoms went as follows:

  • 88 percent had a fever
  • 68 percent had a dry cough
  • 38 percent had fatigue
  • 33 percent coughed up phlegm
  • 19 percent had shortness of breath
  • 15 percent had joint or muscle pain
  • 14 percent had a sore throat
  • 14 percent headache
  • 11 percent had chills
  • 5 percent had nausea or vomiting
  • 5 percent had nasal congestion
  • 4 percent had diarrhea
  • Less than one percent coughed up blood or blood-stained mucus
  • Less than one percent had watery eyes

That data was published in a report by a band of international health experts assembled by the WHO and Chinese officials (called the WHO-China Joint mission), who toured the country for a few weeks in February to assess the outbreak and response efforts.
How severe is the infection?
Most people infected will have a mild illness and recover completely in two weeks.
In an epidemiological study of 44,672 confirmed cases in China, authored by an emergency response team of epidemiologists and published by the Chinese CDC, researchers reported that about 81 percent of cases were considered mild. The researchers defined mild cases as those ranging from the slightest symptoms to mild pneumonia. None of the mild cases were fatal; all recovered.
Otherwise, about 14 percent were considered severe, which was defined as cases with difficult or labored breathing, an increased rate of breathing, and decreased blood oxygen levels. None of the severe cases were fatal; all recovered.
Nearly 5 percent of cases were considered critical. These cases included respiratory failure, septic shock, and/or multiple organ dysfunction or failure. About half of these patients died.
Finally, 257 cases (0.6 percent) lacked severity data.
The overall fatality rate in the patients examined was 2.3 percent.
Who is most at risk of getting critically ill and dying?
Your risk of becoming severely ill and dying increases with age and underlying health conditions.
In the group of 44,672 cases discussed above, the highest fatality rates were among those aged 60 and above. People aged 60 to 69 had a fatality rate of 3.6 percent. The 70 to 79 age group had a fatality rate of about 8 percent, and those 80 or older had a fatality rate of nearly 15 percent.
Additionally, the researchers had information about other health conditions for 20,812 of the 44,672 patients. Of those with additional medical information available, 15,536 said they had no underlying health conditions. The fatality rate among that group was 0.9 percent.
Enlarge/ Graph showing the percentage of cases by age group (blue) and the fatality rates within each age group (orange).
The fatality rates were much higher among the remaining 5,279 patients who reported some underlying health conditions. Those who reported cardiovascular disease had a fatality rate of 10.5 percent. For patients with diabetes, the fatality rate was 7.3 percent. Patients with chronic respiratory disease had a rate of 6.3 percent. Patients with high blood pressure had a fatality rate of 6.0 percent and cancer patients had a rate of 5.6 percent.
Puzzlingly, men had a higher fatality rate than women. In the study, 2.8 percent of adult male patients died compared with a 1.7 percent fatality rate among female patients.
Are men more at risk?
In multiple studies, researchers have noted higher case numbers in men than in women. The WHO Joint Mission report found that men made up 51 percent of cases. Another study of 1,099 patients found that men made up 58 percent of cases.
So far, it is unclear if these numbers are real or if they would even out if researchers looked at larger numbers of cases. Its also unclear if this bias may reflect differences in exposure rates, underlying health conditions, or smoking rates that may make men more susceptible.
That said, sex differences have been seen in illnesses caused by SARS-CoV-2s relatives, SARS-CoV and MERS-CoV. There is some preliminary research looking into this in mice. Some findings suggest that there may be a protective effect from the activity of the female hormone estrogen. Other research has also suggested that genes found on the X chromosome that are involved in modulating immune responses to viruses may also serve to better protect genetically female people, who have two X chromosomes, compared with genetic males, who have only one X chromosome.
Are children less at risk?
Yes, it appears so. In all of the studies and data so far, children make up tiny fractions of the cases and have very few reported deaths. In the 44,672 cases examined by the Chinese CDC, less than one percent were in children ages 0 to 9 years old. None of those cases was fatal. Similar findings have been reported in other studies.
The WHO-China Joint Mission report also noted that children appear largely unscathed in this epidemic, writing, disease in children appears to be relatively rare and mild. From the data so far, they report that infected children have largely been identified through contact tracing in households of adults.
An unpublished, un-peer-reviewed study of 391 cases in Shenzhen, China, seems to support that observation. It noted that within households, children appeared just as likely to get infected as adults, but they had milder cases. The study was posted March 4 on a medical preprint server.
Still, as the Joint Mission report noted, given the data available, it is not possible to determine the extent of infection among children and what role that plays in driving the spread of disease and the epidemic overall. Of note, the report went on, people interviewed by the Joint Mission Team could not recall episodes in which transmission occurred from a child to an adult.
  Are pregnant women at high risk? [NEW, 3/19/2020] 
The question of risks for pregnant women is, unfortunately, very difficult to answer right now. We simply dont have much data.
So far, from the scant data we have, theres little indication that pregnant women are at an increased risk of COVID-19. That is, pregnant women do not appear to have more severe disease than the rest of the population. And there have been no reported deaths of pregnant women due to COVID-19 at this time.
However, pregnant women are at increased risk of getting severely ill or dying from other respiratory infections, such as flu and SARS (which is caused by SARS-CoV, a coronavirus related to SARS-CoV-2, the virus that causes COVID-19). As such, The American College of Obstetricians and Gynecologists (ACOG) currently (as of 3/19) recommends that pregnant women be considered an at-risk population.
The US Centers for Disease Control and Prevention and other health agencies stress that pregnant women should strictly follow the same hygiene measures and social distancing recommended to prevent contracting the virus.
If a pregnant woman does contract the virus, heres what we know so far:
For pregnant women:
Youll most likely have mild to moderate symptoms, like the rest of the population. However, severe symptomsparticularly if you have underlying health conditionscan occur and should be promptly identified and treated.
In a non-peer-reviewed, unpublished study of 34 pregnant women with COVID-19 (16 laboratory confirmed and 18 suspected cases), none of the women developed severe disease. While the women had a higher rate of maternal complications than a control group, all of the complications developed prior to their COVID-19 cases. Those complications included gestational diabetes, premature rupture of membranes, and preeclampsia.
There is a report of a pregnant woman developing severe disease. She was admitted to the hospital at 34 weeks and had an emergency C-section of a stillborn baby before being transferred to the ICU with multiple organ dysfunction and acute respiratory distress syndrome.
For the fetus:
There is no evidence of increased risk of miscarriage or early-pregnancy loss.
There are reports of preterm birth, but it is so far unclear if those early births were due to COVID-19 in the mother.
There is no evidence that the virus infects in utero. In one small study, samples of amniotic fluid, cord blood, neonatal throat swab, and breastmilk from six pregnant women with laboratory-confirmed cases of COVID-19 were all negative for SARS-CoV-2. In another study, three placentas from pregnant women with COVID-19 also tested negative. And in other studies, newborns from symptomatic mothers tested negative for the virus.
There have been a few reports of newborn babies testing positive for the virus, but when they were infected remains unclear. It is possible that they were infected just after birth.
Expert opinion is that there is no intrauterine fetal infection. As such, it is considered unlikely that COVID-19 in a mother would lead to congenital effects from SARS-CoV-2 on the fetus.
How long does COVID-19 last?
On average, it takes five to six days from the day you are infected with SARS-CoV-2 until you develop symptoms of COVID-19. This pre-symptomatic periodalso known as “incubation”can range from one to 14 days.
From there, those with mild disease tend to recover in about two weeks, while those with more severe cases can take three to six weeks to recover, according to WHO Director-General Dr. Tedros Adhanom Ghebreyesus, who goes by Dr. Tedros.
How many people die from the infection?
This is a difficult question to answer. The bottom line is that we dont really know.
Case fatality rates (CFR)that is, the number of infected people who will die from the infectionare simply calculated by dividing the number of dead by the number of recovered plus dead. The CFRs youve probably seen so far have likely been a crude version of this: deaths divided by total cases.
One problem with these crude calculations is that the cases were counting arent all resolved. Some of the patients who are currently sick may later go on to die. In that situation, the patients’ cases are counted, but their deaths are not (yet). This skews the current calculation to make the CFR look artificially low.
But a much larger concern is that we are undercounting the number of cases overall. Because most of the COVID-19 cases that we know about are mild, health experts suspect that many more infected people have not presented themselves to healthcare providers to be tested. They may have mistaken their COVID-19 case for a common cold or didnt notice it at all. In areas hard hit by COVID-19, there may not have been enough testing capacity to detect all of the mild cases. If a large number of mild cases are being missed in the total case count, it could make the CFR look artificially high.
The best way to clear up this uncertainty is to wait until one of the local outbreaks is completely over and then to do blood tests on the general population to see how many people were infected. Those blood tests would look for antibodies that target SARS-CoV-2. (Antibodies are Y-shaped proteins that the immune system makes to help identify and attack pathogens and other unfriendly invaders.) The presence of antibodies against a specific germ in a persons blood indicates that the person has been exposed to that germ, either through infection or immunization. Screening the general population for SARS-CoV-2 antibodies will give a clearer picture of how many people were actually infectedregardless of whether they were symptomatic or diagnosed while sick. That number can then be used to calculate an accurate CFR.
So far, some preliminary population screening for COVID-19 infections has been done in China, specifically in Guangdong province. Screening of 320,000 people who went to a fever clinic suggested that we may not be missing a vast number of mild cases. This in turn suggests that the CFRs we are calculating now are not wildly higher than they should be. However, experts still suspect that many mild cases are going unreported, and many still anticipate that the true CFR will be lower than what we are calculating now.
Beyond getting the basic number of cases and deaths right, CFRs are also tricky because they can vary by population, time, and place. Weve already noted above that the CFR increases in patient populations based on age, gender, and underlying health. But as time goes on, healthcare providers will get collectively better at identifying and treating patients, thereby lowering the CFR.
Complicating these statistics further, the quality of healthcare differs from place to place. The CFR in a resource-poor hospital may be higher than that in a resource-rich hospital. Additionally, health systems overwhelmed in an outbreak may not be able to provide optimal care for every patient, artificially increasing the CFR in those places.
This seems to be what weve seen in China so far. In the WHO-China Joint Mission report, the experts noted that in Wuhanwhere the outbreak began and where health systems have been crushed by the number of casesthe CFR was a whopping 5.8 percent. The rest of China at the time had a CFR of 0.7 percent.
As of March 5, there were about 13,000 cases and 400 deaths reported outside of Chinas Hubei Province (where Wuhan is located). A crude calculation puts the CFR around 3 percent, but this calculation will likely drift throughout the outbreak. We will update the current crude CFR periodically.