As scientists learn more about the latest COVID-19 variant, omicron, they say its origin and spread demonstrate the crucial importance of vaccination.

Many scientists believe omicron originated in South Africa, in a patient with a severely compromised immune system. The virus continued to mutate as the patient’s body struggled to clear the virus. The origin story is one of several hypotheses, and one that should send a strong message about the importance of world vaccination.

“This really has to be about vaccinating the world,” said Carlos del Rio, president-elect of the board of directors for the Infectious Diseases Society of America, which represents infectious disease specialists.

Since first identified in South Africa in late November, omicron cases have been reported in Europe, Canada, and Australia. The United States reported its first confirmed omicron case Wednesday in a California resident who had been vaccinated.

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Researchers do not yet know if omicron is more contagious or causes more severe illness than delta, the most common variant. But they are particularly concerned about omicron because it has a high number of mutations in its spike protein. The spike protein is what enables a virus to infect human cells, and with lots of mutations in its spike protein, scientists are unsure whether people’s existing antibody levels from vaccination or a previous infection will be enough to protect them from severe illness.

Travel bans, like the restrictions the United States put in place earlier this week preventing travel between the U.S. and South Africa and neighboring countries, may slow the spread, but vaccination is the only way to prevent new, more contagious variants from developing, said del Rio, who is executive associate dean for Emory at Grady Health System in Georgia.

“It probably started way before we detected it. By late November when you implement travel bans, you’re closing the barn once the horses are out,” he said.

Vaccination protects individuals from contracting the virus but also reduces the virus’ options for mutating into new variants.

People should continue to practice social distancing, wear masks, avoid crowds, and focus on improving ventilation if gathering indoors, said Julie Vaishampayan, a public health officer from Stanislaus County, Calif.

“We’ve heard these things so many times, but they really do work,” said Vaishampayan, who is chair of IDSA’s public health committee.

Getting the vaccine to parts of the world where vaccination rates have lagged is critical, del Rio said.

Omicron’s journey from South Africa to countries on the other side of the world shows how quickly a new variant can threaten everyone, he said.

So far, omicron has primarily affected young adults and travelers — two groups that are generally fairly healthy — and people have experienced mild or moderate illness.

Misinformation is among the biggest challenges to vaccinating young people, who may have heard the vaccine will affect fertility (it won’t) or that vaccines containing mRNA can alter DNA (they can’t), he said.

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“We need to remind them [the virus is] not benign among young people,” del Rio said. “You don’t need to wind up in the ICU, you don’t need to die. There’s a way to do it, and that’s getting vaccinated.”