title: Impact of birth weight at term on rates of emergency room visits and hospital admissions following vaccination at 2 months of age.
abstract: BACKGROUND
  Birth weight of children born at term may theoretically be associated with risk of adverse events from immunization.
  
  
  METHODS
  We analyzed data on children born between April 1st 2002 and March 31st 2009 in the province of Ontario. Using the self-controlled case series design, we examined the risk of the combined endpoint of emergency room visit and hospital admission in the immediate three days post vaccination at 2 months of age compared to a control period 9-18 days after vaccination. In term children, we conducted 4 comparisons of relative incidence (RI) of events: (1) 4 lower birth weight quintiles compared to the largest quintile (2) SGA10 infants compared to non SGA10 infants, (3) low birth weight infants (<2500g) compared to non low birth weight infants and (4) SGA10 infants vaccinated before 60 days compared to those vaccinated after 60 days.
  
  
  RESULTS
  There was a significant trend towards increasing relative incidence of the combined endpoint with decreasing birth weight quintile (p=0.016). There was an increased relative incidence of events in SGA10 versus non SGA10 infants (RI 1.25 (95% CI 1.09-1.44)) and in SGA10 children vaccinated before 60 days of age compared to after 60 days of age (RI 1.57 (95% CI 1.14-2.18)). No significant effect was observed in low birth weight children. The impact of birth weight was primarily mediated through an increase in ER visits in the 24h following vaccination.
  
  
  CONCLUSIONS
  Lower birth weight appears to be correlated with an increased risk of emergency room visits within 24h of vaccination. The absolute risk is small and there was no impact on admissions or death.
authors: Department of Medicine, Ottawa Hospital Research Institute, University of Ottawa, Canada. kwilson@ohri.ca
authors: Kumanan
authors: K
authors: Wilson
authors: Steven
authors: S
authors: Hawken
authors: Jeffrey C
authors: JC
authors: Kwong
authors: Shelley L
authors: SL
authors: Deeks
authors: Doug G
authors: DG
authors: Manuel
authors: Kirsten Holdt
authors: KH
authors: Henningsen
authors: Natasha S
authors: NS
authors: Crowcroft
mesh_terms: D001724:Birth Weight; D004632:Emergency Medical Services; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D009864:Ontario; D018570:Risk Assessment; D014611:Vaccination / Q000009:adverse effects*