Emily Harrison

The Covid-19 pandemic elevated global attention to the complex problem of allocating and disseminating newly approved vaccines. Following early calls for vaccine equity,1 global health leaders made progress but struggled to fully realize distribution goals.2 With respect to vaccination rates, low and middle income countries have not achieved full parity with high income countries.3 In this issue, Harmon, Kholina, and Graham follow longstanding critiques of market-based vaccine procurement to propose “legal and practical solutions for realizing a new access to vaccines environment”4 that will, they suggest, further the goal of global health justice.

Infection by a temperate phage can lead to death of the bacterial cell, but sometimes these phages integrate into the bacterial chromosome, offering the potential for a more long-lasting relationship to be established. Here we define three major ecological and evolutionary benefits of temperate phage for bacteria: as agents of horizontal gene transfer, as sources of genetic variation for evolutionary innovation, and as weapons of bacterial competition. We suggest that a coevolutionary perspective is required to understand the roles of temperate phages in bacterial populations. The dual personality of temperate phages – as infectious lytic phages or prophages integrated within the bacterial genome – creates a complex interaction with bacterial hosts. Although potentially lethal, prophages confer a multitude of benefits for the host, suggesting the potential for both conflict and collaboration which must be viewed from a coevolutionary perspective that considers both host and phage fitness interests.