Despite suspension from the market in 2005 over concerns about its long-term protection against hepatitis B, infants vaccinated with hexavac have maintained immunity at least 5 years after primary vaccination. These findings published in an Article Online First in The Lancet Infectious Diseases suggest that booster vaccinations are not needed to ensure long-term protection.
In 2000, hexavac and infanrix hexa were licensed in the European Union for vaccinating children against diphtheria, tetanus, whooping cough, polio, hepatitis B, and invasive infections caused by Haemophilus influenzae b. In 2005, hexavac was suspended because of concerns over its ability to provide long-term protection against hepatitis B. Until its suspension in 2005, 10 million doses of hexavac were distributed globally. Yet it is not known whether infants vaccinated with hexavac have maintained protection or will require a booster vaccination to sustain immunity. In this study, an Italian team led by Alessandro Zanetti from the University of Milan in Italy assessed the duration of immunity from vaccination with hexavac and infanrix hexa by testing whether concentrations of antibodies against hepatitis B were retained in 1543 children who had been vaccinated 5 years previously (833 with hexavac and 710 with infanrix hexa), and whether a booster vaccination was needed.
At the start of the study, blood samples were taken from each child to measure levels of antibodies (anti-HBs) against hepatitis B. Children with anti-HBs concentrations of 10 mIU/mL or higher were deemed immune. Children with levels of antibodies less than 10 mIU/mL were randomly assigned to a booster vaccine and tested 2 weeks later.
5 years after primary immunisation, 38.4% of children who received hexavac had protective concentrations of antibodies (≥10 mIU/mL) compared with 83.2% of children who received infanix hexa.
However, children in both groups who received a booster vaccination had a similar rapid anamnestic response*, and the proportion of children who responded to the booster were similar between groups—92.1% of children originally given hexavac and 94.3% of children originally given infanrix hexa showed protective levels of antibodies after the booster vaccination.
Side-effects were infrequent, mild, and did not differ between the two booster groups. No serious adverse events were reported.
These results suggest that infant immune systems are able to recall responding to hepatitis B more than 5 years after primary immunisation with hexavalent vaccines, thereby providing effective protection even in children showing low or undetectable levels of antibodies. The authors conclude: "At present routine booster doses of hepatitis B vaccine do not seem necessary to sustain immunity in children vaccinated with hexavalent vaccines…However, additional follow-up…is required to identify whether immunological memory persists during adolescence and adulthood or whether a booster might be needed later in life to maintain lifelong protection."
Professor Alessandro Zanetti, University of Milan, Milan, Italy. T) +39 02 5031 5126 E) alessandro.zanetti@unimi.it
For full Article see: http://press.thelancet.com/tlidhepb.pdf
Notes to Editors: *An anamnestic response is the renewed rapid production of an antibody after the subsequent encounter with the same antigen. In this study it was defined as an increase in anti-HBs level of four times or more after the booster vaccine, or providing an antibody concentration of at least 10 mIU/mL after the booster vaccine.
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Journal
The Lancet Infectious Diseases