Unlike SARS-CoV-2, which mutated into new strains in its first year as a human disease-causing virus, measles virus does not mutate in a comparable way. A person who is fully vaccinated against the measles virus will usually be protected for life. Now, with a Cell Reports Medicine publication, Mayo Clinic scientists think they know why measles doesn't escape control of the immune system.

In a study led by Miguel Ángel Muñoz-Alía, Ph.D., the team created a large panel of measles virus variants with engineered mutations affecting the proteins on the surface of the virus that the human immune system recognizes and targets via antibodies. They studied the ability of these variants to evade antibodies that neutralize the virus. The authors conclude that there is a near-zero probability for the natural emergence of a new measles virus capable of evading vaccine-induced immunity.

The data presented in the manuscript show that, to escape immunity, a disease-causing, or pathogenic, measles virus would need to generate a large set of mutations — simultaneously — affecting multiple parts of the surface proteins. Simultaneous disruption of at least five antibody targets is required before the virus starts developing resistance to the diversity of neutralizing antibodies in the bloodstream. The authors have characterized the probability of this occurrence as "vanishingly small." Further, they found that even if a measles virus were to mutate extraordinarily and escape neutralizing antibodies in the blood of a vaccinated person, the resulting strain could not cause disease. It would have lost the ability to bind its receptors which are the "keys" to the "doors" in and out of a cell (read more about one door, called nectin-4, in a 2019 article). Funding for this effort was provided by Al and Mary Agnes McQuinn and Mayo Clinic.

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