The virus that causes COVID-19 is not the same strain as what first emerged from China. A new study shows it has changed slightly in a way that makes it more contagious to humans.
Compared to the original strain, people infected with the new strain — called 614G — have higher viral loads in their nose and throat, though they don’t seem to get any sicker. But they are much more contagious to others.
“That kind of makes sense,” says Ralph Baric, PhD, a professor of epidemiology, microbiology, and immunology at the University of North Carolina at Chapel Hill.
The new strain has a change to its spike proteins — the regions of its outer shell that dock on our cells and infect them. The change makes it a much more efficient predator. It passes quickly from cell to cell in our bodies, copying itself at a furious pace.
Baric’s experiments help to explain why the 614G strain, which first emerged in Europe in February, has quickly dominated worldwide spread.
He says the virus likely jumped out of bats and discovered a brand new population of human hosts, with more than 7 billion of us on the planet to infect. None of us has any immune defenses against it, so we are prime targets. Viruses with genetic advantages that help them copy themselves faster and jump more quickly between hosts are the versions that survive and will get passed on.
“So it can jump from person to person to person to person, that’s going to be the most competitive virus in terms of the virus maintaining itself,” says Baric, who is one of the world’s foremost experts on coronaviruses. His new study is published in the journal Science.
The new study backs up earlier research by a team of scientists led by Bette Korber, PhD, at Los Alamos National Laboratory in New Mexico. The team first noticed the rapid spread of the new strain and questioned whether the virus wasn’t evolving to become more easily passed between people.
In new experiments, animals infected with the new 614G strain passed it much more quickly to healthy animals than those infected with the original strain.