Safety of Tdap vaccine in pregnant women: an observational study

Petousis-Harris, Helen; Walls, Tony; Watson, Donna; Paynter, Janine; Graham, Patricia; Turner, Nikki

We found differences in the reporting of swelling and erythema between our groups. There were fewer reports of erythema in the Southern group, and while there were similar numbers of reports of swelling, the timing for onset may have been more imprecise. Given the differences in the reported pain onset and resolution between the groups, it is likely that recall for details of minor local reactions became more prone to recall bias as time progressed and in the absence of a diary to record the details. While in previous clinical studies headache has tended to be reported by around a third of participants, 24 25 27-30 fewer than 3.9% of our participants reported either headache or feeling dizzy. Also, few of our participants reported any gastrointestinal symptoms (2.8%). Almost all systemic events in our study occurred in the 24 h following immunisation as opposed to later, and we consider them likely to be vaccine related. Overall, there were few systemic events reported and the rates of the most common are consistent with those reported in the US study with 33 participants. 31 In our study, one-third to one-quarter of those who reported systemic events had also received the influenza vaccine at the same time. Northern participants reporting systemic events were consistently more likely to have received co-administered influenza vaccine than Southern participants. Most of the reported fevers in our Northern participants also occurred after co-administration with influenza vaccine. Some influenza vaccines are known to be more pyrogenic than others, so it is possible that influenza vaccine was the cause of these excess reports, particularly as the fevers occurred within 24 h after vaccination. 21 The safety of co-administration of influenza vaccine and Tdap in pregnancy has been assessed by the Vaccine Safety Datalink Project, and no excess medically attended events occurred among women receiving both vaccines together compared with sequential vaccination. 6 However, it cannot be assumed that these vaccines have the same reactogenicity profiles.