Repeat COVID-19 cases could offer clues about people’s immunity to the novel coronavirus and how to vaccinate against it.

A handful of factors tip the scales in making a virus more likely to trigger a disruptive global outbreak. Right now, scientists tend to rank influenza, coronaviruses, and Nipah virus as the biggest threats.

In rare instances, the live virus in oral polio vaccines can mutate and become infectious, causing new outbreaks.

Scientists spent five years reconstructing what is now the oldest HIV-1 genome yet recovered.

Tiny insects carry the tomato spotted wilt virus, which causes infected plants to develop discolored ring-shape blotches.

Analyses of more than 300 ancient human genomes show that Hepatitis B virus has infected humans for at least 4,500 years and has much older origins than modern viral genomes would suggest.

Using epidemiological and laboratory data, scientists have mapped out a sequence of mutations through which the attenuated oral polio vaccine reverts to a virulent virus.

Genetic diversity helped avian influenza A viruses make the leap from birds to humans, researchers report.

Tracking the genetic diversity and evolution of rhinoviruses can lead to a better understanding of viral evolution, the common cold, and more dangerous infections.