The Covid pandemic was an extraordinary moment in history. Starting at the end of 2019, a virus new to science swept across the planet, killed more than 25 million people and caused trillion of dollars in economic damage.
But as outbreaks go, Covid was pretty ordinary, a new study finds.
Scientists compared seven viral outbreaks that occurred in recent decades, including epidemics of Covid, Ebola and influenza. For the most part, the researchers found, the outbreaks were not preceded by any unusual genetic changes in the viruses. In all but one case, in 1977, the viruses circulated in animals and gained the ability to spread to and among people only by unfortunate coincidence.
“We see that time and again,” said Joel Wertheim, a virologist at the University of California San Diego. He and his colleagues published the study on Friday in the journal Cell.
Dr. Wertheim and his colleagues reconstructed the evolutionary history of these viruses by looking at their genes. They tracked how viruses gained different kinds of mutations before causing outbreaks and looked at that pattern after the viruses jumped into the human population.
In one line of research, the scientists examined the influenza pandemic of 2009. In that year, a new strain of influenza emerged in North America and went on to infect one-quarter of all people on Earth and kill 230,000.
Other studies of the virus have revealed that it came from pigs, where influenza viruses gain mutations on a regular basis. Some mutations made it harder for the viruses to spread to other pigs. Others provided an evolutionary edge; still others had no effect.
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