According to a new review article published in Cell Host & Microbe, it is challenging to create vaccines that offer long-lasting defense against influenza, coronaviruses, and respiratory syncytial virus (RSV). The flu, RSV, SARS-CoV-2, and "common cold" coronaviruses all share several traits that make them capable of causing repeated re-infections, in contrast to the respiratory viruses that cause measles, mumps, and rubella.

These traits include extremely quick host-to-host transmission and rapid replication, especially in the nasal mucosa. Researchers pointed out that these viruses lack systemic replication; hence, they do not fully activate the adaptive immune response. As a result, new understanding on several fronts is necessary to develop the next generation of enhanced vaccines against mucosa-replicating viruses.

For instance, more has to be studied about the connections between RSV, coronavirus, and flu viruses, as well as the immune system elements that mostly function in the upper respiratory system. These interactions have changed over time, resulting in "immune tolerance," where the human host tolerates brief, localized viral infections.

According to the authors, mucosal immunization, when possible, seems to be the best method of immunizing against the relevant viruses. However, there are still a lot of information gaps that need to be filled to create effective mucosal vaccines, such as identifying the best vaccine formulations, figuring out dosing amounts and schedules, and creating strategies for overcoming immune resistance. 

(Source: https://theprint.in/health/new-study-explores-challenges-of-developing-mucosal-vaccines-for-respiratory-viruses/1368227/ )