Viruses That Adapt

Viruses constantly accumulate genetic changes as they replicate, and some of those changes can affect how easily they spread or how well our immune defenses recognize them. Influenza is a great example. Scientists developed the first influenza vaccines in the 1940s, but they soon discovered a major challenge: influenza viruses could change enough that a vaccine designed for one strain might not work as well against a newer strain. In the 1946–47 flu season, a significantly different influenza virus circulated, and the vaccine that had worked in previous seasons was no longer effective against it. This helped scientists understand the importance of tracking how influenza viruses change and updating vaccines to better match circulating strains.

Modern genomic sequencing has made this process much faster. Scientists can read the genetic material of viruses and track changes as they appear and spread through populations. And while TB isn't a virus, it is caused by a bacterium, it shows that evolution isn't limited to viruses. Mycobacterium tuberculosis can also evolve drug resistance, making some infections much harder to treat.