A new COVID-19 variant that led to a spike in hospital cases across parts of Asia may now account for more than one-third of all COVID-19 cases in the U.S., health officials say.

The variant, known as NB.1.8.1, has been spreading fast. The U.S. Centers for Disease Control and Prevention estimates that it accounted for nearly half of the cases found in travelers coming into the country during the last week of May.

The agency's airport surveillance program detected the variant in travelers from several countries, CBS News reported.

In that program, international travelers arriving at designated airports volunteered to contribute nasal swab samples and completed a survey, according to the CDC. The samples were then analyzed in a lab to look for variants or mutations important to public health.

Still, the CDC said these new estimates have a wide margin of error and may change as more data come in. But the increase suggested that the variant is spreading — and spreading fast.

"Data indicates that NB.1.8.1 does not lead to more severe illness compared to previous variants, although it appears to have a growth advantage, suggesting it may spread more easily. In other words, it is more transmissible," Subhash Verma, a professor of microbiology and immunology at the University of Nevada, Reno, told CBS News.

The symptoms of NB.1.8.1 are similar to those of earlier COVID variants:

• Cough
• Sore throat
• Fever
• Tiredness

As the virus continues to evolve, access to vaccines may change for some groups.

In May, the U.S. Food and Drug Administration announced that it will still approve updated vaccines for people at higher risk, like seniors and those with health conditions such as pregnancy or diabetes.

But vaccine makers will have to run large new trials before updated shots can be approved for everyone else. This could mean that many healthy adults and children won't have access to a new vaccine this fall, CBS News reported.

U.S. Health and Human Services Secretary Robert F. Kennedy Jr. also said last month that he would remove the CDC's recommendation for healthy pregnant women and children to be vaccinated against COVID-19.

The CDC later said that kids without health problems may still get the vaccine if their parents and doctor agree it's the right choice.

"Where the parent presents with a desire for their child to be vaccinated, children 6 months and older may receive COVID-19 vaccination, informed by the clinical judgment of a healthcare provider and personal preference and circumstances," the CDC stated.