The novel coronavirus is a strain of coronavirus first identified in late 2019 that causes the respiratory illness known as COVID-19. The virus itself is officially named SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), while COVID-19 refers specifically to the disease it produces. On December 31, 2019, health officials in Wuhan, China, reported a cluster of unusual pneumonia cases, and a previously unknown coronavirus was eventually identified as the cause.
Why It’s Called “Novel”
“Novel” simply means new. When the virus first appeared, it had never been seen in humans before, so scientists labeled it a novel coronavirus to distinguish it from the many coronaviruses already known to circulate. Coronaviruses are a large family of viruses, some of which cause nothing more than a common cold, while others cause serious illness. SARS-CoV-2 belongs to a subgroup called sarbecoviruses, the same group that includes the virus behind the 2003 SARS outbreak.
The naming follows a deliberate process. The International Committee on Taxonomy of Viruses named the virus SARS-CoV-2 on February 11, 2020, based on its genetic structure. On the same day, the World Health Organization named the disease COVID-19. Viruses and the diseases they cause often carry different names for different purposes: the virus name helps scientists develop tests and treatments, while the disease name guides public health discussions about prevention and care.
How SARS-CoV-2 Infects the Body
The surface of the virus is studded with spike proteins that act like keys. These spikes latch onto a receptor called ACE2, which sits on the surface of many human cells, particularly in the airways and lungs. Once the spike protein locks onto ACE2, host enzymes help split the spike open, allowing the virus to fuse with the cell membrane and slip inside. From there, it hijacks the cell’s machinery to make copies of itself, which then spread to neighboring cells.
This spike protein is also the target of COVID-19 vaccines. mRNA vaccines deliver lab-made genetic instructions that teach your cells to build a harmless fragment of the spike protein. Your immune system spots that fragment as foreign, produces antibodies against it, and remembers it. If the real virus shows up later, your body can mount a faster defense.
How It Spreads
SARS-CoV-2 spreads primarily through respiratory droplets released when an infected person coughs, sneezes, talks, or breathes. Larger droplets tend to fall to the ground within a short distance, but smaller particles can linger in the air longer and travel farther, especially in poorly ventilated indoor spaces. Early in the pandemic, surface transmission (touching contaminated objects) received significant attention, but airborne and close-contact spread turned out to be far more important routes.
The virus can also be detected in stool, though fecal-oral transmission has not been established as a meaningful route of spread.
How It Compares to SARS and MERS
Three serious coronavirus outbreaks have affected humans in the 21st century, and each behaved very differently. The original SARS virus, which caused the 2003 outbreak, infected 8,098 people worldwide and killed 774, giving it a case fatality rate of about 9.7%. MERS, identified in 2012, is even deadlier at roughly 34% but spreads much less efficiently, with a reproductive number (the average number of people one sick person infects) below 1.
SARS-CoV-2 sits at the other end of that tradeoff. Its estimated reproductive number is about 2.5, meaning it spreads more readily than either SARS or MERS. Its case fatality rate, after accounting for mild and asymptomatic infections, is estimated at around 1%. That lower per-case lethality, combined with much higher transmissibility, is what allowed it to become a global pandemic rather than a contained outbreak.
Symptoms and Incubation Period
Symptoms typically appear 2 to 14 days after exposure. The most common include fever, cough, fatigue, body aches, sore throat, congestion, and loss of taste or smell, though the specific symptom profile has shifted somewhat as new variants have emerged. Vaccination status also influences which symptoms predominate and how severe they become. Many infections, particularly in vaccinated individuals, are mild or produce no symptoms at all, while others can progress to pneumonia, difficulty breathing, and organ damage.
Variants and Ongoing Evolution
Like all viruses, SARS-CoV-2 mutates as it replicates. When mutations cluster in ways that change the virus’s behavior, such as making it more transmissible or better at evading immunity, scientists classify the new lineage as a variant. Early in the pandemic, variants like Alpha, Delta, and Omicron drew global attention for their distinct waves of infection. The virus continues to evolve. As of early 2026, CDC genomic surveillance shows a mix of circulating lineages, with XFG and its sublineages making up over 60% of sequenced cases in the United States and newer lineages like NB.1.8.1 also circulating at significant levels.
Updated vaccines are reformulated periodically to better match the variants currently in circulation, similar to the approach used with seasonal flu vaccines.
Treatment Options
For most people, COVID-19 resolves on its own with rest and symptom management. For those at higher risk of severe illness, including older adults and people with certain underlying conditions, antiviral medications can reduce the chances of hospitalization and death. The most widely used oral antiviral, Paxlovid, is taken at home and must be started within five days of symptom onset. Another oral option, molnupiravir, follows a similar timeline. A third antiviral, remdesivir, is given by IV infusion over three consecutive days and must begin within seven days of symptoms. All of these work by interfering with the virus’s ability to replicate inside the body.
Long COVID
Some people experience symptoms that persist for weeks or months after the initial infection clears. This condition, called Long COVID, can involve fatigue, brain fog, shortness of breath, heart palpitations, joint pain, and dozens of other symptoms affecting nearly every organ system. No single lab test can confirm or rule out Long COVID. Diagnosis is based on a patient’s history, symptoms, and physical exam, sometimes supported by evidence of a prior infection through a positive viral or antibody test. The condition can occur after mild infections as well as severe ones, and researchers are still working to understand why some people develop it while others recover fully.