A new pathogen has been introduced into our species, and in some form, it will now circulate among us forever.

Once in the lungs, the virus kills the cells that line the alveoli, little globular sacs that are responsible for oxygen exchange. Blood and fluid leak from the injured lung tissue into the sacs, which makes patients short of breath. They drown in their own fluids.

Only seven types of the coronavirus are known to infect humans. Four of them cause the common cold. Two of those four, OC43 and HKU1, originally came from rodents, and the other two, 229E and NL 63, came from bats. The other three types that afflict human beings are SARS-1, SARS-2, and Middle East respiratory syndrome, known as MERS.

These changes occur at fairly regular intervals, like a molecular clock—one tiny mutation every two weeks, on average. Since those mutations happen at random places in the code, the genome of a virus in one part of the world will be slightly different than it is in other parts. By studying these cumulative, haphazard mutations collected from many t

The latent period is often shorter than the incubation period in SARS-2, but that was generally not the case in SARS-1. The difference between the latent period and the incubation period is sometimes known as the mismatch period; it’s calculated by measuring the incubation period and subtracting the latent period. The difference between these two p

In terms of evolutionary biology, the virus has had what is known as an “ecological release.” This refers to the expansion of range and the population explosion that occurs when a species is freed from constraints it previously faced. The typical example of this is invasive species introduced by humans such as the cane toads that overwhelmed Austra

Distinguishing among such alternatives is also difficult because it is not always possible to be absolutely certain. A key reason for this is that the rapid rate at which people transmit SARS-2 (the average interval between one person contracting it and then transmitting it to someone else is about a week) is faster than the rate at which the virus

However, because of the scarcity of tests, the CDC initially recommended that people with respiratory complaints be tested only if they had a travel history to China or an exposure to a known COVID-19 case, guidance that would persist until February 27. As a result, in the six weeks after the identification of Patient Zero, only fifty-nine other ca

Scientists later came to suspect that this initial move by the virus might have happened at the Huanan Seafood Wholesale Market in Wuhan, because many of the first recorded patients were vendors or visitors there. But the picture was confusing. Huanan is known as a wet market because, as at many other markets throughout the world, one can buy fresh