The Food and Drug Administration said on Monday that the modified Covid-19 vaccines against new, emerging variants may be authorized without the need for lengthy clinical trials.

The new guidance, released in a 24-page document on the FDA’s website, would clear the new vaccines as an amendment to a company’s originally approved emergency use application, according to the FDA.

The company would need to submit new data that shows the modified vaccine produces a similar immune response and is safe, similar to the process for annual flu vaccines.

“Preliminary reports from clinical trials evaluating COVID-19 vaccine candidates in multiple countries including South Africa have added to concerns that vaccine efficacy against the B.1.351 variant may be lower than against the original virus,” the agency wrote in the document, referring to the strain found in South Africa. “Thus, there is an urgent need to initiate development and evaluation of vaccines against these SARSCoV-2 variants.”

The updated guidance comes as U.S. health officials, including White House Chief Medical Advisor Dr. Anthony Fauci, are concerned the virus potentially could mutate enough to evade the protection of current vaccines and reverse the progress made on the pandemic.

In recent weeks, officials have pushed Americans to get vaccinated as quickly as possible before potentially new and even more dangerous variants of the virus emerge.

Public health officials and infectious disease experts have said there is a high likelihood that Covid-19 will become an endemic disease, meaning it will never fully go away, though it will likely spread at lower levels than it is now. Health officials will have to continuously watch for new variants of the virus, so scientists can produce vaccines to fight them, medical experts say.