As a measles outbreak expands across the US, comments by health secretary Robert F Kennedy Jr have come under scrutiny. Kennedy has said that the best way to prevent measles is to get vaccinated – but he has also caused alarm among paediatricians, vaccine experts and lawmakers by promoting vitamin A and nutrition as treatments for measles and questioning the safety testing of the MMR vaccine. He also recently announced a US-led scientific effort to establish the cause of what he terms the ‘autism epidemic’, with some experts concerned that this study will support the widely discredited association between autism and vaccines. US health reporter Jessica Glenza tells Ian Sample, the Guardian’s science editor, how these mixed messages are already impacting scientific research.