<unk> , immune<unk> , immune evasion or<unk>  mutation occurs when the immune system of a host, especially of a human being, is unable to respond to an infectious agent: the host's immune system is no longer able to recognize and eliminate a pathogen, such as a virus. This process can occur in a number of different ways of both a genetic and an environmental nature. Such mechanisms include homologous recombination, and manipulation and resistance of the host's immune responses. Different antigens are able to<unk>  through a variety of mechanisms. For example, the African trypanosome parasites are able to clear the host's antibodies, as well as resist lysis and inhibit parts of the innate immune response. A bacteria, Bordetella pertussis, is able to<unk>  the immune response by inhibiting neutrophils and macrophages from invading the infection site early on. One cause of<unk>  is that a pathogen's epitopes (the binding sites for immune cells) become too similar to a person's naturally occurring MHC-1 epitopes, resulting in the immune system becoming unable to distinguish the infection from self-cells.<unk>  is not only crucial for the host's natural immune response, but also for the resistance against vaccinations. The problem of<unk>  has greatly deterred the process of creating new vaccines. Because vaccines generally cover a small ratio of strains of one virus, the recombination of antigenic DNA that lead to diverse pathogens allows these invaders to resist even newly developed vaccinations. Some antigens may even target pathways different from those the vaccine had originally intended to target. Recent research on many vaccines, including the malaria vaccine, has focused on how to anticipate this diversity and create vaccinations that can cover a broader spectrum of antigenic variation. On 12 May 2021, scientists reported to The United States Congress of the continuing threat of COVID-19 variants and COVID-19<unk>  mutations, such as the E484K virus mutation.
Antigenic escape
Cross-tolerance
Antigenic variation
Immune tolerance
Seroconversion
Host adaptation
Molecular mimicry
Functional specialization 