About 40 percent of children around the globe suffer from anaemia because they do not consume enough iron. Now, studies by ETH researchers show that iron deficiency also reduces the protection provided by vaccinations. Despite the fact that global immunisation programmes are now reaching more people than ever, about 1.5 million children still die every year from diseases that vaccination could have prevented. Vaccination is also less effective in low-income countries than in high-income countries, although it is not yet clear why. Findings from two clinical studies with children in Kenya now suggest that iron deficiency during infancy may reduce the protection that vaccinations provide.