As bad as delta is, could the next COVID variant be worse?
We were so close to conquering COVID-19.
Now, as delta sweeps the world, experts worry: What future version of the virus could expand its infectious empire?
“The big concern is that the next variant that might emerge — just a few mutations potentially away — could potentially evade our vaccines,” Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said last week.
All viruses constantly change into new versions of themselves. With each generation, they make random genetic errors.
They don’t mean to cause trouble. They have no dreams of greatness, said Dr. Joel Ernst, professor of medicine and chief of the Division of Experimental Medicine at UC San Francisco.
“All they want to do is replicate,” he said. Citing the pioneering work of Stanford microbiologist Stanley Falkow, Ernst said, “The goal of a virus is to become viruses.”
Early on, we weren’t too worried about changes to the SARSCoV-2 virus’ genetic makeup, stored in a single strand of RNA. Compared with flu and HIV, the virus changes slowly as it spreads.
But now we know that any change can have serious consequence.
Delta serves as a textbook example. Its genetic code not only carries some of the successful mutations of earlier variants but also the ability to spread twice as fast, churning out many more progeny.
Data indicate that delta is 40 percent to 60 percent more transmissible than alpha and almost twice as transmissible as the original Wuhan strain. Furthermore, it grows at higher levels inside the throat and lungs than did earlier versions of the virus.
With only 49.3 percent of the U.S. population fully vaccinated, this trait is proving key to the delta’s continued evolution and spread.
“It’s sobering,” said virologist Shane Crotty of the Vaccine Discovery Division at La Jolla Institute
for Immunology. Variants “alpha and delta are six months apart from each other. Each managed to become much more infectious.
“That definitely makes it less certain about what the virus can do in the future,” he said.
The most risky changes involve the virus’ spike protein, which lets the virus latch onto human cells and gain entry, causing infection.
“The concern is that each mutation might make it a little bit more able to bind,” said infectious disease expert Dr. Julie Parsonnet, professor of medicine at Stanford University.
So far, the virus has been notably uncreative at evading our vaccines, with just a limited repertoire of changes. For instance, despite being separated by thousands of miles, the delta variant first discovered in India and a variant most common in California used the same mutation to try to dodge our antibodies. Variants that independently emerged in South Africa and Brazil also share a mutation.
“There are a handful of ways that the virus has mutated to avoid some of the antibody response,” none of them very effective, Crotty said. “And it keeps coming up with them over and over again. And so far, that doesn’t appear to be a big problem.”
But there are troubling signs of increased virulence. The death rate associated with alpha, or the U.K. variant, was about 64 percent higher than previous variants. Now, compared to alpha, the delta variant doubles the risk of hospitalization among the unvaccinated, based on new Scottish data. Scientists don’t know if that is because of a genetic change or simply because it grows so rapidly.
To quickly detect the next mutation that could alter the trajectory of the pandemic, the U.S. must more fully harness the power of genomics, said experts.
Only close surveillance through gene sequencing will tell us if the virus has taken another big jump.
“At some point,” Ernst said, “it’s likely that the virus will reach the point that it’s tried out everything. And we respond.”
“There will be some equilibrium,” he said, “but I don’t know where that is.”