If infectious diseases were a monarchy, measles might be king. Not only does measles reign among the most contagious diseases known to man – likely to infect any non-vaccinated individual who stands in the same room as an infected person – measles has long been known to be one of the great killers of children. Before vaccination, measles was responsible for millions of childhood deaths. Today it remains a cause of great illness and death in low-resource countries, killing over 140,000 children worldwide every year.

Where measles vaccines have been introduced, childhood deaths often plummet by as much as 50%. Measles is deadly, but before the vaccines were introduced in 1963, the virus did not directly cause half of all childhood disease deaths. In other words, where measles vaccines have been introduced, they were associated with reductions in more childhood disease deaths than were actually caused by the measles.

The reason for these major drops in mortality has been a central mystery surrounding the vaccine for decades. My colleagues and I wanted to take a step toward further unraveling this mystery.

We figure, as have others, that there are two ways that the measles vaccine could prevent more deaths than are strictly due to measles virus.

  1. The vaccine itself could have long-lasting non-specific immune-boosting properties that protect the recipient from other diseases.

  2. The measles infection could have long-lasting effects that predispose someone to other diseases.