Editor—Slack and Schapira1 are correct in drawing attention to a problem that is recognised and documented but not fully addressed or understood. Their suggestion that further studies are required to determine the optimum timing of immunisation for extremely preterm infants is sound (even though the adequate immunological response of these babies to vaccinations is well documented).

However they state that the presumed cause of the apnoeas is the pertussis component, with neither reference nor explanation of why they think this is the case. As the four antigens are given simultaneously it is not possible to identify the culprit. The American studies quoted2 ,3 could not identify whether one or a combination of antigens …