What are the present challenges and future considerations in developing vaccines against mucosal respiratory viruses?

In a recent review, the former director of the National Institute of Allergy and Infectious Diseases and former chief medical advisor to the president of the United States (U.S.), Dr. Fauci, and his team review the roadblocks to developing effective vaccines against viruses that infect the human respiratory mucosa and discuss strategies for next-generation vaccine development against mucosal respiratory viruses