Decades of research show that depression, stress, loneliness, and poor health behaviours can weaken the body's immune system and lowers the effectiveness of certain vaccines. A new report suggests that the same may be true for the new Covid-19 vaccines that are in development and the early stages of global distribution.

The report was published in Perspectives on Psychological Science. Fortunately, it may be possible to reduce these negative effects with simple steps like exercise and sleep. The key to their success, however, is ensuring that a critical percentage of the population is effectively vaccinated to achieve so-called herd immunity.