Table 4.

List of unique adverse event definitions provided by selected studies. Only adverse events explicitly defined by study authors (i.e., those studies defining AEFIs beyond simply referring to the coding/classification scheme used) are shown. Definitions with an asterisk are those used in studies conducted in lower-middle-income countries (LMICs).

AEFI target (mother, neonate, fetus)	AEFI type	AEFI type, detail	AEFI definition, description, or classification reference used [references]
Mother	Local	Local reaction	Pain, redness, or swelling [82] Redness, swelling, induration or pain confirmed by comparison to a 2 cm circle (≥circle records as positive) [21]
	Systemic	Anaphylaxis	Physician assessment or Brighton definition [57,58] Sudden onset (<3d after vaccination) and rapid progression of symptoms involving multiple systems organ classes: dermatologic, cardiovascular, and respiratory (per Brighton collaboration definition) [40]
		Bell’s palsy	Brighton definition [57,58]
		Fever	“Feeling feverish” and/or temperature measured to be >100.4°F [82] Temperature ≥ 38 °C [51,52]
		Guillain-Barre syndrome	Physician assessment or Brighton definition [57,58]
		Influenza-like illness	Oral temperature > 37.8 °C with at least one influenza-like symptom (cough, sore throat, rhinorrhea, nasal obstruction) [50]
		Mild adverse event	Headache, fever, or myalgia [81]
	Pregnancy-related	Abnormal pregnancy	Ectopic pregnancy/spontaneous abortion/stillborn delivery [87]
		Maternal death	Death from direct or indirect obstetric causes during pregnancy or <42 days after pregnancy termination [20]*
		Normal pregnancy	Normal, live-born delivery [87]
		Pre-eclampsia	Pregnancies with an ICD-9-CM-coded diagnosis of preeclampsia (642.4×–642.7×) occurring during pregnancy [39]
		Pregnancy complications	Any or none, based on self-report [75]
		Preterm labor	Pregnancies with an ICD-9-CM-coded diagnosis of threatened premature labor (hereafter referred to as premature labor; 644.0×) or early (spontaneous) onset of delivery occurring during pregnancy with initial diagnosis of either premature labor or premature delivery at least 1 day after pandemic H1N1 or seasonal influenza immunization [39]
		Severe acute maternal morbidity	Direct or indirect obstetric complications that threaten the woman’s survival but do not lead to her death [20]*
Fetus	In utero	Elective abortion	Induced termination of a pregnancy due to personal choice or medical reasons prior to 20 weeks post-conception day (or 22 weeks of gestation) [83]
		Fetal death	Spontaneous abortion and stillbirth combined [42] Nonviable conceptus in pregnancies after more than 20 weeks amenorrhea [72]
		Induced abortion	Therapeutic or elective abortion [87]
		Intrauterine fetal death	Fetal death with unknown gestation time [57,58]
		Late fetal death	Fetal death occurring ≥20 w gestation [88]
		Miscarriage/spontaneous abortion	Abortion occurring between start of week 7 and end of week 22 of gestation [22] Any non-deliberate interruption of an intrauterine pregnancy before the 28th week of gestation (since the last menstrual period) in which the fetus is dead when expelled (WHO 1970)[23] Delivery between 14 w and 21 w + 6 days gestation [50] Delivery prior to 20 weeks [34] Fetal death occurring <20 weeks gestation [57–59,61,91,92] Intrauterine death of a fetus under 500 g or of gestational age under 22 weeks’ amenorrhea [37] Intrauterine death of fetus at <24 w gestation [83] Loss before 22 weeks gestation [24] Pregnancy loss before week 22 [43] Pregnancy termination within 20 weeks of conception [18]* Spontaneous loss of conceptus before 20 weeks amenorrhea [42] Spontaneous pregnancy loss at <20 gestational weeks [36] Termination of a pregnancy without human interference prior to 20 weeks post-conception day (or 22 weeks of gestation) [84] Loss of a fetus <500 g or prior to 22 weeks gestation [75]
		Stillbirth	Death at birth [20]* Delivery of a non-viable fetus at or after 20 weeks [34] Delivery of a non-viable fetus at or after 22 completed weeks [72] Fetal death occurring >20 weeks gestation [57,58] Fetal death of ≥500 g [57–60] Fetal demise ≥20 w gestation [91,92] Fetus born after 20 weeks gestation without pulse [18]* Intrauterine death of a fetus over 500 g or of gestational age more than 22 weeks’ amenorrhea [37] Intrauterine death of fetus at ≥24 w gestation [83] Loss of a fetus ≥500 g or at 22 weeks gestation or later [75] Pregnancy loss after week 22 [43]
Neonate	Congenital abnormality	Gross malformation	Physical defect present in baby at birth, including any abnormality visible on a naked baby (e.g. cleft lip or palate, Down syndrome, spina bifida, limb defects, etc.) [43]
		“Various”	Classified using CDC and Prevention Metropolitan Atlanta Congenital Defects Program guidelines. All structural–morphological, chromosomal or genetic anomalies were included in this definition, regardless of whether the fetus was delivered dead or alive, and included birth defects identified by prenatal ultrasound, amniocentesis or examination of the products of conception after elective or spontaneous abortion [83]
	Perinatal	Early neonatal death	Death of a liveborn infant within the first week of life [20]*
		Low Apgar score	Score < 7 at 5 min [50,54]
		Low birth weight	Birth weight < 2500 g [22,54,75,84] Birth weight < 2500 g measured by study team within 7 days of life or extracted from official birth records [20]*
		Postterm birth	Birth 42 weeks or greater [43]
		Preterm birth	Birth ≤ 36 completed weeks [54] Birth at <37 weeks gestation [75,84] Birth between 22 w and 36 w + 6 days gestation [50] Birth between 32 and 36 weeks [43] Clinical estimate of gestational age at birth of less than 37 completed weeks [29] Estimated gestational age <37 completed weeks as determined by ultrasound, last menstrual period, or validated exam within 7 days of life [20]* Live birth <37 weeks gestation [91,92]
		Small for gestational age	<10th percentile for sex and gestational age in live born infants using standard US growth charts for full and preterm infants (NCHS 2000 growth curves or Lubchenko) [36] <10th percentile of gestational age-specific birth weight within cohort [54,66] Brenner’s standard for fetal growth less than the 10th percentile [34] Children with measurements of weight, length, and head circumference <2 SD than reference values (calculated from full-term infant measurements of combined reference cohorts) [45] Lowest 10th percentile of birth weight for each gestational week [29] Measurements <2 SD from expected weight [47]
		Very low birth weight	Birth weight under 1500 g [42]
		Very preterm birth	Birth between 22 and 31 weeks [43] Birth less than 32 weeks gestation [42]
	Postnatal	Atypical infant behavior	Deviation from normal feeding, crying, defecating, urinating, sleeping, and growing behavior as defined by mother [18]*
		Infant death	Live births dying later in infancy [18]*
		Late neonatal death	Death of a liveborn infant between 1 and 4 weeks of life [20]*
		Recurring illness	Illness lasting more than two weeks or occurring twice or more often [18]*