KEYWORD1:
vaccination delay; healthy vaccinee effect; adverse events

BACKGROUND:
Providers may delay vaccination when children are ill. Therefore, children may likely be healthiest at the time of vaccination. Many research studies investigating adverse events following vaccination compare the health of a child before and after vaccination. If a child is more likely to be healthy prior to vaccine administration, the risk estimates from such research designs may be biased.

OBJECTIVE:
To determine, for one clinical scenario:
1. How frequently physicians delay vaccinations.
2. Which vaccines physicians commonly delay.
3. Length of time physicians delay vaccinations.

METHOD:
Surveys were sent to 154 providers at Kaiser Permanente Colorado - 81 responded (53%). Providers replied to a hypothetical scenario where children at 3 different ages (1, 5, and 12 years) were recently diagnosed with idiopathic thrombocytopenic purpura (ITP) and were due for routine vaccinations.
Providers responded to 3 questions:
· Would you delay any vaccinations?
· Which vaccines would you delay?
· How long would you delay these vaccinations?

RESULT:
When presented with the scenario of the 1-year-old child, providers chose to delay more vaccinations for longer periods of time compared to older children. Providers would delay vaccination from 2 weeks to 6 months (all ages); the mean delay was 34 days. Regardless of age, providers chose to delay MMR and varicella vaccinations approximately 50% of the time. Nearly 37% of providers chose not to withhold any vaccinations for children of all 3 ages.

CONCLUSION:
Our results suggest that there is considerable variability among immunization practices of providers when presented with patients recently diagnosed with ITP. Because providers are reluctant to vaccinate children with recent illnesses, children could be of above average health in the weeks immediately prior to vaccination. We refer to this as the 'Healthy Vaccinee Effect'.
LEARNINGOBJECTIVES:
To describe immunization practices after an acute illness.