Giving influenza and pertussis (whooping cough) vaccines on the same day during pregnancy was not associated with higher rates of adverse pregnancy, birth, or newborn outcomes, according to a new population-based cohort study published late last week in JAMA Network Open.
For the study, researchers from Sydney Children’s Hospitals Network analyzed perinatal, immunization, and hospitalization data for singleton pregnancies in New South Wales, Australia. The team compared 6,959 pregnant women who received flu and pertussis vaccines concomitantly (on the same day) at 20 weeks’ gestation or later with 6,959 matched women who received just the pertussis vaccine.
Matching was based on vaccination date, gestational age at vaccination, and maternal age. The pregnancies occurred in 2021 and 2022. Mean maternal age at the time of delivery was 31.7 years.
Among participants who received both vaccines on the same day, 3.8% of pregnancies ended in preterm birth, compared with 4.4% in the pertussis-only group. Among live, full-term births, 8.8% of infants in the concomitant group were small for gestational age, compared with 9.9% in the control group, and low birth weight occurred in 1.7% of infants in the concomitant group and 1.6% of infants in the control group.
“No association was found between concomitant influenza- and pertussis-containing vaccine administration during pregnancy and an increased rate of adverse pregnancy, birth, or neonatal outcomes compared with pertussis vaccination alone,” the authors write.
More vaccines recommended during pregnancy
The authors note that same-day vaccination is often encouraged as a way to boost vaccine uptake, especially as an increasing number of vaccines are recommended during pregnancy, including those against flu, pertussis, tetanus, COVID-19, and respiratory syncytial virus (RSV).
Studies looking at short-term side effects suggest that getting the flu and tetanus-diphtheria-acellular pertussis (TDaP) vaccines at the same time during pregnancy leads to slightly more mild, short-term reactions like soreness at the injection site or headaches, compared with getting the vaccines separately. But the available evidence does not show an increased risk of fever or serious adverse events that require medical care in the days after vaccination.
But few studies have focused on how getting two vaccines at once affect pregnancy, birth, and newborn outcomes, note the authors, and safety concerns remain a barrier to vaccine uptake in pregnancy. The researchers hope the current study findings can help clinicians more confidently recommend same-day vaccination.
Findings counter concerns about same-day vaccination
Theoretical concerns related to same-day vaccinations include stronger adverse events, like high fever, that could lead to future health problems for newborns.
This study didn’t find evidence of that—in fact, the findings suggest that women who got both vaccines at the same time may have had slightly lower risks of certain negative outcomes than those who got only the pertussis vaccine.
But, the researchers caution, the difference might not be caused by the vaccines. It might be related to other factors, including the possibility that people who got both vaccines are more engaged with health care overall, which alone could lead to better health outcomes, or that getting the flu vaccine earlier in pregnancy has protective benefits for mothers and newborns.
Overall, however, the findings offer support for the idea that same-day vaccination is safe during pregnancy.
“The evidence presented may help clinicians more confidently recommend pregnancy vaccination concomitantly and potentially provide more opportunities to optimize uptake,” the authors write. “Our study is particularly relevant considering the recent availability of the maternal RSV vaccine, which in many countries is the third (or fourth) vaccine recommended at any time in pregnancy and the second vaccine specifically targeted to the latter half of pregnancy.”
