Two new subvariants of the Omicron strain now make up 70% of the United States' COVID cases, according to the CDC. 

The variants, known as BA.4 and BA.5, are reportedly the most contagious to date. 

Officials say currently available COVID vaccines offer strong protection to severe illness, but it appears BA.5 evades some protection offered by the shots and prior infection. 

Vaccine manufacturers are currently working on Omicron specific COVID shots, which are expected to be made available in the fall.