Pretty easy to find:
https://www.federalregister.gov/documents/2019/09/24/2019-20804/modernizing-influenza-vaccines-in-the-united-states-to-promote-national-security-and-public-health
Why I stand corrected. Although it does not indicate a prohibition on the use of egg based vaccine development, it does appear the trend is strong in the use of alternatives...I guess that would be mRNA.
Thanx