Understanding the immune response to highly variable viruses

Understanding how the immune response develops towards these infections can guide how to develop effective vaccines that prevent infection. One arm of our immune response results in the development of neutralizing antibodies that stick to the pathogen and prevent the pathogen from infecting our cells. Neutralizing antibodies are a key component of all effective human vaccines. However, their effectiveness is compromised when pathogens evolve to generate changes that prevent the antibodies from sticking. 

Pandemic pathogens such as SARS-COV-2 and hepatitis C are examples of highly variable viruses that confound the immune response by evading the neutralizing antibody response. As a result, re-infection can occur in the case of SAR-COV-2 when pre-existing immunity (either from vaccination or infection) is no longer matched to new circulating strains. In the case of hepatitis C, 70% of people exposed to the virus develop a lifelong infection and even in those who clear infection, reinfection can occur. There is no vaccine to prevent hepatitis C.