Get ready to learn more Greek letters. Scientists warn that omicron’s whirlwind advance practically ensures it won’t be the last version of the coronavirus to worry the world.

Every infection provides a chance for the virus to mutate, and omicron has an edge its predecessors: It spreads way faster despite emerging on a planet with a stronger patchwork of immunity from vaccines and prior illness.

That means more people in whom the virus can further evolve. Experts don’t know what the next variants will look like or how they might shape the pandemic, but they say there’s no guarantee the sequels of omicron will cause milder illness or that existing vaccines will work against them.

They urge wider vaccination now, while today’s shots still work.

“The faster omicron spreads, the more opportunities there are for mutation, potentially leading to more variants,” Leonardo Martinez, an infectious disease epidemiologist at Boston University, said.

Since it emerged in mid-November, omicron has raced across the globe like fire through dry grass. Research shows the variant is at least twice as contagious as delta and at least four times as contagious as the original version of the virus.

Omicron is more likely than delta to re-infect individuals who previously had COVID-19 and to cause “breakthrough infections” in vaccinated people while also attacking the unvaccinated. The World Health Organization reported a record 15 million new COVID-19 cases for the week of Jan. 3-9, a 55% increase from the previous week.

Along with keeping comparatively healthy people out of work and school, the ease with which the variant spreads increases the odds the virus will infect and linger inside people with weakened immune systems – giving it more time to develop potent mutations.

“It’s the longer, persistent infections that seem to be the most likely breeding grounds for new variants,” said Dr. Stuart Campbell Ray, an infectious disease expert at Johns Hopkins University. “It’s only when you have very widespread infection that you’re going to provide the opportunity for that to occur.”

Because omicron appears to cause less severe disease than delta, its behaviour has kindled hope that it could be the start of a trend that eventually makes the virus milder like a common cold.

When new variants do develop, scientists said it’s still very difficult to know from genetic features which ones might take off. For example, omicron has many more mutations than previous variants, around 30 in the spike protein that lets it attach to human cells. But the so-called IHU variant identified in France and being monitored by the WHO has 46 mutations and doesn’t seem to have spread much at all.

To curb the emergence of variants, scientists stress continuing with public health measures such as masking and getting vaccinated. While omicron is better able to evade immunity than delta, experts said, vaccines still offer protection and booster shots greatly reduce serious illness, hospitalizations and deaths.

Experts say the virus won’t become endemic like the flu as long as global vaccination rates are so low. During a recent press conference, WHO Director-General Tedros Adhanom Ghebreyesus said that protecting people from future variants — including those that may be fully resistant to today’s shots — depends on ending global vaccine inequity.

Tedros said he’d like to see 70% of people in every country vaccinated by mid-year. Currently, there are dozens of countries where less than a quarter of the population is fully vaccinated, according to Johns Hopkins University statistics. And in the United States, many people continue to resist available vaccines.

“These huge unvaccinated swaths in the U.S., Africa, Asia, Latin America and elsewhere are basically variant factories,” said Dr. Prabhat Jha of the Centre for Global Health Research at St. Michael’s Hospital in Toronto. “It’s been a colossal failure in global leadership that we have not been able to do this.”

In the meantime, new variants are inevitable, said Louis Mansky, director of the Institute for Molecular Virology at the University of Minnesota.

With so many unvaccinated people, he said, “the virus is still kind of in control of what’s going on.”