There are two main challenges to developing an effective oral vaccine: * designing a formulation that can survive the harsh gastrointestinal environment. For e

There are two main challenges to developing an effective oral vaccine: * designing a formulation that can survive the harsh gastrointestinal environment. For example, COVID-19 vaccines, especially the mRNA-based ones, are especially fragile and degrade rapidly at room temperature even under normal conditions. * Avoiding mucosal tolerance. Many antigens that would evoke an immediate immune response if encountered in the blood stream are ignored by mucus tissue, to avoid your body creating hundreds or thousands of spurious immune responses every day to antigens occurring in your food. For an oral vaccine to be effective it must get around this tolerance to provoke an effective immune response. For respiratory viruses, another promising delivery method would be intranasal, and indeed there are some COVID-19 vaccines in development that use this route[1]. The bottom line is, developing vaccines is already complicated and costly, so unless there is a guaranteed large market demand pharmaceutical companies are unlikely to invest in delivery methods that add additional research challenges. [1] https://www.gavi.org/vaccineswork/covid-19-vaccines-could-squirt-nose-be-just-good-shot-arm https://www.gavi.org/vaccineswork/covid-19-vaccines-could-sq...