Bacteriophages, or phages, are viruses that specifically infect and destroy bacteria, presenting a potential solution for treating antibiotic-resistant infections. These microscopic entities operate by attaching to bacterial cells, injecting their genetic material, and using the host's machinery to replicate. This process culminates in the lysis, or bursting, of the bacterial cell, releasing new phages to continue the cycle.

A vaccine is a biological product that can be used to safely induce an immune response that confers protection against an infection and/or disease on subsequent exposure to a pathogen. To achieve this, the vaccine must contain antigens that are either derived from the pathogen or produced synthetically to represent components of the pathogen.

Viral mutation rates play a pivotal role in vaccine development. Mutation rate refers to how often genetic changes occur in a virus’s genome during replication. All vaccines trigger immunity, but how long it lasts depends on several factors. One of the important ones is the rate at which a virus replicates. If a virus replicates quickly, it has a chance to produce more mutations, also known as variants. The more variants emerge, the harder it is to make a vaccine that will create lasting immunity, because the target keeps moving. If a virus is stable, that gives us a big advantage. Measles is an example of a stable virus that is unlikely to replicate, so scientists could predict that immunity would last a long time, which it does." Smallpox and polio, highly contagious viruses that were almost eradicated through vaccination, are also stable with low mutation rates.