The CDC recommend that all people wear cloth face masks in public places where it is difficult to maintain a 6-foot distance from others. This will help slow the spread of the virus from asymptomatic people or people who do not know they have contracted the virus. Cloth face masks should be worn while continuing to practice social distancing. Instructions for making masks at home can be found here. Note: It is critical that surgical masks and N95 respirators are reserved for healthcare workers.

This article was updated on April 6, 2020

In December last year, reports started to emerge that a coronavirus that specialists had never before seen in humans had begun to spread among the population of Wuhan, a large city in the Chinese province of Hubei.

Since then, the virus has spread to other countries, both in and outside Asia, leading the World Health Organization (WHO) to declare this as a pandemic.

To date, the novel coronavirus — currently dubbed “severe acute respiratory syndrome coronavirus 2,” or SARS-CoV-2 for short — has been responsible for more than 1,000,000 infections globally, causing over 70,000 deaths. The U.S. is the most affected country.

But what do we really know about this virus? And how is it likely to affect the global population?

Medical News Today have contacted the WHO, used the information that public health organizations have offered, and looked at the newest studies that have featured in peer-reviewed journals to answer these and other questions from our readers.

Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

1. What is the new virus?

SARS-CoV-2 is a coronavirus that causes coronavirus disease 2019 (COVID-19). Coronaviruses, in general, are a family of viruses that target and affect mammals’ respiratory systems. According to their specific characteristics, there are four main “ranks” (genera) of coronaviruses, which are called alpha, beta, delta, and gamma.

Most of these only affect animals, but a few can also pass to humans. Those that are transmissible to humans belong to only two of these genera: alpha and beta.

Only two coronaviruses have previously caused global outbreaks. The first of these was the SARS coronavirus — responsible for severe acute respiratory syndrome (SARS) — which first started spreading back in 2002, also in China. The SARS virus epidemic primarily affected the populations of mainland China and Hong Kong, and it died off in 2003.

The other one was the MERS coronavirus — or Middle East respiratory syndrome coronavirus — which emerged in Saudi Arabia in 2012. This virus has affected at least 2,494 people since then.

2. Where did the virus originate?

When humans do become infected with a coronavirus, this typically happens via contact with an infected animal.

Some of the most common carriers are bats, although they do not typically transmit coronaviruses directly to humans. Instead, the transmission might occur via an “intermediary” animal, which will usually — though not always — be a domestic one.

The SARS coronavirus spread to humans via civet cats, while the MERS virus spread via dromedaries. However, it can be difficult to determine the animal from which a coronavirus infection first starts spreading.

In the case of the new coronavirus, initial reports from China tied the outbreak to a seafood market in central Wuhan. As a result, local authorities closed down the market on January 1.

However, later assessments have since suggested that this market was unlikely to be the single source of the coronavirus outbreak, as some of the people infected with the virus had not been frequenting the market.

Specialists have not yet been able to determine the true source of the virus or even confirm whether there was a single original reservoir.

When MNT contacted the WHO for comment, their spokespeople emphasized:

“We don’t yet know [what the specific source of SARS-CoV-2 was]. Researchers in China are studying this but have not yet identified a source.”

3. How is the virus transmitted?

While it likely originated in animals, the transmission of the new coronavirus from person to person can occur, though some questions about its transmission remain unanswered.

According to the WHO spokespeople who responded to MNT queries, “[r]esearchers are still studying the exact parameters of human-to-human transmission.”

“In Wuhan at the beginning of the outbreak, some people became ill from exposure to a source, most likely an animal, carrying the disease. This has been followed by transmission between people,” they explained, adding:

“As with other coronaviruses, the transmission is through the respiratory route, meaning the virus is concentrated in the airways (nose and lungs) and can pass to another person via droplets from their nose or mouth, for example. We still need more analysis of the epidemiological data to understand the full extent of this transmission and how people are infected.”

In a press briefing from February 6, WHO consultant Dr. Maria Van Kerkhove said that, for now, “[w]e do know that mild individuals shed virus, we know that severe individuals shed virus. […] We know that the more symptoms you have, the more likely you are to transmit.”

In their “Q&A on coronaviruses,” the WHO state that “[t]he risk of catching COVID-19 from someone with no symptoms at all is very low. However, many people with COVID-19 experience only mild symptoms. […] It is therefore possible to catch COVID-19 from someone who has, for example, just a mild cough and does not feel ill.”

In an interview for the JAMA Network — also broadcast on February 6 — Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said that based on data that they have received from Chinese specialists, the new coronavirus’s “incubation period is probably between 5 and 6 — maybe closer to 5 — days.

That is, the virus likely takes about 5–6 days to give rise to symptoms once it has infected a person.

Although the WHO note that experts estimate that the new virus’s incubation period may last anywhere between 1 and 14 days, they suggest in their coronavirus Q&A section that the most likely duration is about 5 days.

4. How does it compare with other viruses?

Researchers from Chinese institutions were able to use state-of-the-art genome sequencing tools to identify the DNA structure of the novel coronavirus.

It has emerged that SARS-CoV-2 is most similar to two bat coronaviruses known as bat-SL-CoVZC45 and bat-SL-CoVZXC21 — its genomic sequence is 88% the same as theirs.

The same study shows that the new virus’s DNA is about 79% the same as that of the SARS coronavirus and approximately 50% like that of the MERS virus.

Recently, a study by researchers in China suggested that pangolins may have been the initial propagators of SARS-CoV-2, as its genomic sequence appeared to be 99% like that of a coronavirus specific to these animals.

Since then, however, other specialists have cast doubts over this idea, citing inconclusive evidence.