New genetic variations of the coronavirus disease 2019 (Covid-19) represent a significant challenge to efforts to bring an end to the pandemic, Dr. Anthony Fauci said Monday.

However, currently available vaccines from Pfizer-BioNTech and Moderna, as well as those in development at AstraZeneca, Johnson & Johnson and Novavax, appear to be effective at preventing serious illness from the virus, he said.

That may mean people may have to accept experiencing mild symptoms of the disease, even after vaccination, according to Fauci, director of the US National Institute of Allergy and Infectious Diseases.

“Obviously, you want to get as high an efficacy as you can for [a vaccine against] any form of disease,” he said in an address during the annual meeting of the American Association for the Advancement of Science, held virtually because of the pandemic.

However, if a vaccine “can keep you out of the hospital … [or] keep you from getting seriously ill … that’s a big deal,” he said.

Medical experts identified new strains of the coronavirus in the fall, most notably one in England, which is referred to as the “UK variant” or B.1.1.7 strain, and another in South Africa, called the 1.351 strain.

Although new strains of Covid-19 were “inevitable,” given that all viruses mutate, “we are being challenged by [them] now” as they spread across the United States, Fuci said.

The UK variant is believed to be more contagious than the original strains of the virus first found in Wuhan, China, while the “problematic” South Africa strain appears to be less responsive to current vaccines.

However, that does not mean that vaccines fail to offer at least some protection against these strains, Fauci said.

The Pfizer-BioNTech vaccine, for example, was found to offer protection against serious illness from the South Africa strain with “slightly lower” efficacy compared to the Wuhan strains, a study published Monday by Nature Medicine found.

Similarly, the Johnson & Johnson vaccine, which is being evaluated by the US Food and Drug Administration, offers 57-percent protection against the South African strain, compared to 72 percent with the Wuhan strain, Fauci said.

Still, the vaccine prevented severe disease from the South Africa strain in 88 percent of those who received it, and no one who had the shot was hospitalized or died from the virus, he said.

The ultimate goal is a “universal vaccine” against all coronaviruses and “these are already in the works,” Fauci said.