A more contagious virus means the vaccination target has to be much higher, perhaps in the range of 90%
Since late 2020, the US has been overrun by a succession of coronavirus variants, each with its own suite of mutations conferring slightly different viral traits. For much of this year, the Alpha variant looked like the clear winner. In second place was Iota, followed by Gamma, Beta and Epsilon.
Then came Delta, but was much slower in transmission at the outset in the country. Today, it has nearly wiped out all of its rivals, accounting for 93.4% of new infections by July, reports The Washington Post.
The speed with which it dominated the pandemic has left scientists nervous about what the virus will do next. The variant battles of 2021 are part of a longer war, one that is far from over.
Epidemiologists had hoped getting 70 or 80% of the population vaccinated, in combination with immunity from natural infections, would bring the virus under control. But a more contagious virus means the vaccination target has to be much higher, perhaps in the range of 90%.
Globally, that could take years. In the US, the target may be impossible to reach anytime soon given the hardened vaccine resistance in a sizable fraction of the country, the fact that children under 12 remain ineligible and the persistent circulation of disinformation about vaccines and the pandemic.
With so many people unvaccinated around the world, the virus has abundant opportunity not only to spread and sicken large numbers of people, but to mutate further. Some scientists have expressed hope that the virus has reached peak "fitness," but there is no evidence this is so.
Delta's meteoric takeover of the pandemic in the US brought a jarring, premature end to a summer of relative freedom from the global viral emergency. Just as schools and workplaces were ready to hit reset and embrace a level of normalcy, indoor mask-wearing is back in much of the country, regardless of vaccination status.
Hospitals in states with low vaccination rates are struggling to cope with a flood of patients. At the same time, vaccination rates are jumping as the reality of the pandemic and the efficacy of the vaccines overcome fear, inertia and disinformation.
Most laboratory research has focused on the spike protein the virus uses to enter cells. But Delta has mutations that affect other regions - and little is known about what they do.
"Nobody knows what tricks the virus has left," said Jeremy Luban, a virologist at the University of Massachusetts Medical School. "It's possible we've seen all of its chess moves, or its poker tricks, but it's got a very big complicated genome and it probably still has some space to explore."
Like everyone else, scientists are wondering when SARS-CoV-2's contagiousness will peak.
"Delta surprised me," said Trevor Bedford, an expert on viral evolution at the Fred Hutchinson Cancer Research Center. "This doesn't happen with an influenza pandemic. It doesn't happen with Ebola. It doesn't happen with most other things."
He knows it can't keep evolving to become more transmissible forever. Eventually, the virus will hit a ceiling, he said.
"But it's not exactly clear what that is."