Thirty-three prospective studies were included in the review: 13 before-and-after studies (n=3,588), seven quasi-experimental studies (n=1,764); and 13 randomised controlled trials (RCTs) (n=2,040). Sample size of included studies ranged from 24 to 1,406 participants. The authors reported that all studies were deemed to be of similar quality.
Meta-analysis (five RCTs, n=757 participants): Participants who received hepatitis B vaccination intradermally were 14% less likely to achieve seroprotection than those who received the vaccine intramuscularly (RR 0.86, 95% CI 0.77 to 0.95). The level of heterogeneity was statistically significant (Χ2=12.06, p=0.017).
Narrative synthesis: The 13 before-and-after studies reported seroprotection rates that ranged from 68% to 100% with intradermal vaccine. In the seven quasi-experimental studies seroprotection ranged from 41% to 100% with intradermal vaccine and 87.5% to 100% with intramuscular vaccine. In the 13 RCTs, the rate of seroprotection was generally lower in the intradermal vaccine group compared with the intramuscular group.
Children and infants (six studies): In the four comparative studies, intradermal vaccine was associated with lower seroprotection than intramuscular vaccine (41% to 98% compared with 94% to 100%). In two before-and-after studies, intradermal vaccine offered 93% to 100% seroprotection. Overall, the rates of seroprotection in children and adults were higher than in adults.
Gender (six studies): The seroprotection offered by intradermal injection was marginally higher in adult females (89% to 100%) than adult males (64% to 100%).