Tuesday, March 18, 2008

Birth weight and reported adverse events following immunization

Tracy N. Thomas, CDC/OCSO/ISO, CDC, 1600 Clifton Road NE, MS D-26, Atlanta, GA, USA

Learning Objectives for this Presentation:
By the end of the presentation, participants will be able to:
1. Name common adverse events reported among children less than 6 years old.
2. Determine if birth weight is associated with reporting of specific adverse events following vaccination.

Although low birth weight (LBW) infants may be partially immunocompromised, vaccination of LBW infants is generally thought to be effective and safe. However, few studies have examined the safety profile among vaccinated LBW infants.

To compare the frequency and types of adverse events (AEs) reported among normal birth weight (NBW), LBW and very low birth weight (VLBW) infants.

Reviewed data from the Vaccine Adverse Event Reporting System (VAERS) in children < 6 years vaccinated from Jan 1, 2000 thru December 31, 2006. NBW, LBW, and VLBW were defined as > 2500g, 1500-2500g and < 1500g, respectively. We compared reporting of non-serious and serious AEs, defined according to federal regulatory criteria, by birth weight (BW) status. Main outcome measures were proportions of commonly reported adverse events and rates of serious AE (SAE), by BW status.

Reported AEs were similar across birth weight categories and primarily consisted of injection site and systemic reactions including fever (range: 6-10%), injection site redness (range: 1-5%), and rash (range: 1-3%). Frequency of a SAE following a first dose of any vaccination increased with decreasing birth weight groups (NBW-8%; LBW-13%; VLBW-33%). VLBW children < 6 years old consistently had higher rates of reported SAE, with the greatest elevation for the outcome of hospitalization. (OR=7.65; CI: 6.85 8.54). This increased risk of reported hospitalization was also seen among children < 1 (OR=7.32; CI: 6.51 8.23).

Children of LBW may have minimal risk of SAEs; however, data suggest children of VLBW may be at greater risk of experiencing an SAE following vaccination. This may be explained by higher rates of underlying chronic conditions seen among VLBW infants.