TABLE 4

Characteristics of Studies Included in a Systematic Review of the Literature on Early Childhood Health Outcomes Associated With In Utero Exposure to Influenza Vaccines

Author(s) (y), CountryStudy DesignAscertainment of ExposureType of VaccineStudy PeriodAge of Follow-upNo. ParticipantsTrimester of Exposure, n (%)Ascertainment of OutcomeOutcome(s)
ExposedUnexposedFirstSecondThird
Pandemic influenza vaccine
 Bischoff et al41 (2015), DenmarkNested RCTRandom allocationMF59-adjuvanted pandemic A/H1N1 influenza vaccine2009–20100–1 y51332Not specifiedNot specifiedNot specifiedParent-reported daily diary cards reviewed by research doctorInfections (common cold, pharyngitis, otitis, pneumonia, fever, and gastrointestinal infection)
 Ludvigsson et al34 (2015), SwedenProspective cohortRegisterAS03-adjuvanted pandemic A/H1N1 influenza vaccineOctober 2, 2009, to November 26, 20100–6.4 y41 183234 317Not specifiedNot specifiedNot specifiedDeath registerMortality
 van der Maas et al35 (2016), NetherlandsRetrospective cohortSelf-reportMF59-adjuvanted pandemic A/H1N1 influenza vaccineNovember 2009 to December 20090–1 y13576691357 (100) across the second and third trimesterRegister and medical recordsInfection-related primary care contact (fever, symptoms of infection of ≥1 organ system, or prescriptions for infectious symptoms)
 Fell et al36 (2016), CanadaRetrospective cohortRegisterPandemic A/H1N1 influenza vaccineaNovember 2, 2009 to October 31, 20100–1 y36 04481 302Not specifiedNot specifiedNot specifiedMedical recordsInfluenza, combination of pneumonia and influenza
 Hviid et al38 (2017), DenmarkRetrospective cohortRegisterAS03-adjuvanted pandemic A/H1N1 influenza vaccineNovember 2, 2009 to March 31, 20100–5 y631155 048349 (5.5)5962 (94.5) across the second and third trimesterRegister and medical recordsHospitalizations, infectious diseases, autoimmune diseases, neurologic diseases, behavioral disorders
 Walsh et al39 (2019), CanadaRetrospective cohortRegisterPandemic A/H1N1 influenza vaccineaNovember 2, 2009 to October 31, 20100–5 y31 29572 954Not specifiedNot specifiedNot specifiedMedical recordsInfectious diseases, atopic diseases, neoplasms, sensory disorders, urgent and inpatient health services use, complex chronic conditions, mortality
Seasonal influenza vaccine
 Benowitz et al40 (2010), United StatesMatched case-controlMedical recordsIIVOctober 1, 2000 to April 30, 20090–1 y113b1938 (22.2)28 (77.8)Direct fluorescent antibody testLaboratory-confirmed influenza
 van Santen et al33 (2013), United StatesRetrospective cohortMedical recordsTrivalent IIVJune 2, 2002 to December 31, 20090–1 y24167391Not specifiedNot specifiedNot specifiedMedical recordsAcute otitis media, medically attended acute respiratory infections
 Zerbo et al37 (2017), United StatesProspective cohortMedical recordsIIVc2000–20100–15 y45 231151 69813 477 (29.8)17 475 (38.6)16 095 (35.6)Medical recordsAutism spectrum disorder
  • IIV, inactivated influenza vaccine; —, indicates no participants in the exposure group.

  • a Study did not distinguish between non-adjuvanted pandemic influenza vaccine (targeted at pregnant women) and AS03-adjuvanted pandemic influenza vaccine (targeted at the general population).

  • b Number of case participants (infants hospitalized for laboratory-confirmed influenza).

  • c Study included the 2009 A/H1N1 pandemic year; investigators did not distinguish between the seasonal trivalent influenza vaccine from the pandemic monovalent vaccine during this period of time.