WASHINGTON — Contracting the new Omicron variant of the coronavirus Is less likely to lead to severe illness than other variants, like Delta, Dr. Anthony Fauci, the top medical adviser to President Biden, said at a briefing of the White House pandemic response team on Tuesday. He cautioned, however, that much about the variant is not yet certain.

“It appears that with the cases that we have seen, we are not seeing a very severe profile of disease. In fact, it might be — and I underscore ‘might be’ — less severe,” Fauci said, referencing epidemiological reports from South Africa, where some of the first cases of Omicron were detected late last month. The Delta strain has been the dominant variant of the virus in the United States for about six months.

Fauci cautioned that the results that are in so far may have been influenced by the relative youth of the patients in South Africa who contracted the new strain of the disease. This could potentially have masked the variant’s severity, since younger people tend not to display as serious symptoms from COVID-19 as older patients.

The United States has a much higher vaccination rate than South Africa, with 86 percent of Americans over the age of 65 fully vaccinated, according to the Centers for Disease Control and Prevention. In that cohort, 48 percent have also received their booster shots, which are thought to provide extra protection.

Fauci cautioned that the encouraging findings regarding the new strain are preliminary and that it could take several more weeks to fully discern the profile of Omicron, which has a number of concerning mutations. Early indications are that the variant is more transmissible, and that it is probably more likely than previous variants to evade immunity from vaccines or antibodies acquired after previous exposure to COVID-19. But that does not necessarily mean it makes people more sick.

Fauci made similar statements to French outlet AFP on Tuesday, saying that Omicron is “almost certainly is not more severe than Delta.” The Omicron variant has been found in the U.S., but it is so far less prevalent than Delta.