The emergence of a new coronavirus variant in southern Africa rattled much of the world Friday as the United States and other nations scrambled to halt air travel from the region, financial markets plunged, and the World Health Organization hastily met with South African scientists, even as experts in New England and elsewhere cautioned against overreacting.
The WHO named the new strain Omicron and classified it as a variant of concern, the same designation given the now-dominant Delta variant, because it is potentially more transmissible. The group said early evidence suggests that people who already had COVID-19 could be at risk of reinfection from the new variant.
Dr. Anthony Fauci, the nation’s top infectious diseases expert, told CNN on Friday that there’s no evidence the variant has arrived in the United States. He said it has “some mutations that are raising some concern, particularly with regard to possibly transmissibility increase and possibly evasion of immune response.”
Pfizer-BioNTech and Moderna, makers of rival messenger RNA vaccines, said they are ready to develop booster shots tailor-made for Omicron if evidence suggests that current vaccines don’t protect people from the variant.
In South Africa, where only 35 percent of people are fully vaccinated, the variant has begun to spread rapidly, according to a Washington Post report. Thus far, several dozen cases have also been identified in Botswana, Hong Kong, and Israel. But officials from a number of countries warn that the variant may already be spreading undetected.
The United States on Friday swiftly joined the European Union and several other countries in imposing travel restrictions on visitors from southern African nations.
The White House said the United States will restrict travel from South Africa and seven other countries in the region beginning Monday. It did not provide details except to say the restrictions will not apply to returning US citizens or permanent residents, who will continue to be required to test negative for COVID-19 before they travel to the United States.
The emergence of a new variant comes as COVID-19 cases in Massachusetts have risen in recent weeks. In its first report since Wednesday, the state Department of Public Health said Friday that it had logged 5,058 new coronavirus cases and 24 deaths.
Medical experts and organizations, including WHO, stressed that more needs to be learned about how much of a threat Omicron poses. But here and abroad, there were worries that the pandemic could be taking another turn for the worse nearly two years after COVID-19 emerged. So far, the disease has killed more than 5 million people around the globe, including at least 777,000 in the United States.
Several experts noted that some previous variants, such as Beta and Mu, proved less troublesome than scientists initially feared.
“We’ll know more in coming days to weeks,” Dr. Ashish Jha, dean of the Brown University School of Public Health, wrote on Twitter. “There will be those who will spread fear ― and those who downplay it. Please ignore both groups.”
Dr. Dan Barouch, head of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, said he was concerned because the new variant has 30 mutations, a large number, in the spike protein that the virus uses to infect human cells. His researchers first saw Omicron’s genetic sequence on Thanksgiving after South African scientists posted it online. The mutations are concentrated at a location on the virus that antibodies target, he said, which “raises the question as to whether the virus will still be covered by the vaccines.”
The Beth Israel lab helped develop the Johnson & Johnson coronavirus vaccine and has studied the Pfizer-BioNTech and Moderna vaccines. Like other labs around the world, it has begun to synthesize the spike protein of the new variant using the genetic sequence that was posted. But Barouch said it will be several weeks before his lab can run tests to determine if the three vaccines work against Omicron.
Even if Omicron can elude the vaccines, he said, it may not trigger a new wave of infections around the world unless it is also more transmissible than Delta. “There’s so much unknown that it’s not a reason to panic as of today,” he said.
In a statement, Pfizer’s German partner, BioNTech, said it is waiting for more data before deciding on next steps, which include creating a messenger RNA booster tailored for the new variant. The firm said it could do that within six weeks and ship initial batches within 100 days, if necessary.
Moderna, the Cambridge-based maker of a rival mRNA vaccine, said it’s studying whether a higher dose of its current booster or two other boosters that it already created are effective against the new variant. In addition, the company plans to develop an Omicron-specific booster and could begin testing it within two to three months.
The discovery of the variant sent stock markets worldwide sharply down Friday, with the Dow Jones industrial average tumbling more than 2.5 percent in a shortened trading day. Health care stocks were notable exceptions to sell-off, with Moderna adding more than 20 percent to its share price.
Oil prices dropped nearly 12 percent on fears that travel restrictions would affect demand.
The 27-nation European Union on Friday also imposed a temporary ban on air travel from countries in southern Africa.
“The last thing we need is to bring in a new variant that will cause even more problems,” said Germany’s health minister, Jens Spahn. Some European nations, including Germany, have experienced a massive spike in COVID-19 cases recently, apparently unrelated to the new variant.
The EU Commission’s president, Ursula von der Leyen, said flights will have to “be suspended until we have a clear understanding about the danger posed by this new variant, and travelers returning from this region should respect strict quarantine rules.”
She insisted on extreme caution, warning that “mutations could lead to the emergence and spread of even more concerning variants of the virus that could spread worldwide within a few months.” Belgium became the first European Union country to announce a case of the Omicron variant.
Showing how complicated the spread of a variant can be, the Belgian case involved a traveler who returned home from Egypt on Nov. 11 but did not become sick with mild symptoms until Monday, according to professor Marc Van Ranst, who works for the scientific group overseeing the Belgian government’s COVID-19 response.
Israel, one of the most vaccinated countries, announced Friday that it detected its first case of the new variant in a traveler who returned from Malawi. The traveler and two other suspected cases were placed in isolation. Israel said all three were vaccinated, but officials were looking into the travelers’ exact vaccination status.
The Africa Centers for Disease Control and Prevention strongly discouraged any travel bans on countries that reported the new variant. It said past experience shows that such travel bans have “not yielded a meaningful outcome.”
Nonetheless, the United States announced restrictions on visitors from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique, and Malawi, hours after the United Kingdom, Japan, and other governments took similar steps.
Some experts said the variant’s emergence illustrated how rich countries’ hoarding of vaccines threatens to prolong the pandemic.
Fewer than 6 percent of people in Africa have been fully immunized against COVID-19, and millions of health workers and vulnerable populations have yet to receive a single dose. Those conditions can speed up spread of the virus, providing more opportunities for it to evolve into a dangerous variant.
“This is one of the consequences of the inequity in vaccine rollouts and why the grabbing of surplus vaccines by richer countries will inevitably rebound on us all at some point,” said Michael Head, a senior research fellow in global health at Britain’s University of Southampton. He urged Group of 20 leaders “to go beyond vague promises and actually deliver on their commitments to share doses.”
Material from Globe wire services was used in this report.