Richard Massé

Antibody persistence and the effect of a booster dose given 5, 10 or 15 years after vaccinating preadolescents with a recombinant hepatitis B vaccine.

The persistence of antibody obtained post-vaccination of preadolescents with three doses of Engerix-B and the effect of a booster administered 5, 10 or 15 years later were monitored in 663 vaccinees. Five, 10 and 15 years post-vaccination >94% of subjects had detectable antibodies and 88.2%, 86.4% and 76.7% had a titre ≥10 IU/L; GMTs were 269 IU/L, 169 IU/L and 51 IU/L, respectively; 99.1-100% vaccinees reached a titre ≥10 IU/l post-booster. GMTs were 118012 IU/L, 32477 IU/L, and 13946 IU/L when the booster was administered 5, 10 or 15 years post-vaccination, respectively. We conclude that vaccination induces immunity in the great majority of vaccinees for at least 15 years. The response to a booster dose suggests persistence of immune memory in almost all vaccinees. Although a booster dose increases substantially anti-HBs titres, the clinical relevance of such an increase remains unknown. These results do not support the need of a booster for at least 15 years when vaccinating preadolescents with Engerix-B.

Comparative immunogenicity under field conditions of two recombinant hepatitis B vaccines in 8–10-year-old children

The immunogenicity of two hepatitis B vaccines was compared in 8-10-year-old children immunized in a school program. One year apart, 1129 children received Engerix-B 10 microg vaccine (EB), and 1126 received Recombivax-HB 2.5 microg (RB), following the 0, 1, 6 schedule. Blood samples were collected one month after the third dose. Anti-Hbs were measured by commercial radioimmunoassay. In the EB group, 99.1% of the children seroconverted (>/=2 IU/l) compared to 99.7% in the RHB group (p=0.09). The seroprotection rate (>/=10 IU/l) was similar for both groups: 98.9% in the EB group and 99.2% in the RB group (p=0.66). However, GMCs of anti-HBs were higher in children given EB compared to those given RB (7307 vs. 3800 mIU/ml, p<0.0001). This study showed that both vaccines were highly immunogenic, in the course of a regular field immunization program. However, the difference observed in the antibody levels attained according to the vaccine may play a role in the long-term protection of these children.

Most ten-year-old children with negative or unknown histories of chickenpox are immune.

To evaluate the proportion of children to vaccinate against varicella in a catch-up program targeting 9- to 10-year-old children, a study was conducted among children age 10 years to assess the age-specific incidence of varicella and document the immunity against varicella in those with negative or unknown chickenpox history. Of the latter 62% were seropositive for varicella.

Antibody kinetics among 8–10 years old respondents to hepatitis B vaccination in a low endemic country and the effect of a booster dose given 5 or 10 years later

Few data are available concerning the persistence of anti-HBs and the effect of booster doses given several years post-vaccination against hepatitis B during preadolescence. The objective of this open-labelled clinical trial was to evaluate the persistence of antibodies after vaccination with three paediatric doses of Engerix-B at the age of 8-10 years and the effect of a booster dose given 5 (Group Y5) or 10 (Group Y10) years later. Anti-HBs were measured before and one month post-primary vaccination, then 5 and 10 years later, before the booster dose, as well as one month and 1 year post-booster. The anamnestic response was defined as a >or=fourfold increase of anti-HBs post-booster (>or=10 IU/L) when compared to pre-booster. Ten years post-primary vaccination, 559 of the 652 initially randomized subjects (86%) were eligible for analysis. Group Y5, 5 years post-booster results: 99% of subjects had detectable levels of antibodies and 96% a titer >or=10 IU/L. The anti-HBs GMTs decreased from 114,489 IU/L one month post-booster to 3354 IU/L 5 years later. Group Y10 results: 10 years post-primary vaccination 96% of subjects had a detectable level of anti-HBs and 85% were above the threshold of 10 IU/L. The GMTs one month post-booster were 31,030 IU/L. The challenge with a booster demonstrated an anamnestic response in 99% of subjects in group Y5 and 100% of subjects in group Y10. All subjects were anti-HBc negative. The booster doses were well tolerated. The excellent anamnestic response observed after the booster dose demonstrates the persistence of immunity in virtually all young adults vaccinated at the age of 8-10 with three paediatric doses of Engerix-B.

Coxiella burnetii seroprevalence of shepherds and their flocks in the lower Saint-Lawrence River region of Quebec, Canada.

OBJECTIVE To determine the seroprevalence of Coxiella burnetii among the shepherds and their sheep in the lower Saint-Lawrence River region (LSLRR) of Quebec, Canada. DESIGN A prospective human-animal comparative study was conducted with 81 shepherds from 46 farms and a control group matched for sex and age. All participants answered a standardized questionnaire to evaluate their risk factors for Q fever, including a specific section on the work practices of the shepherds. All human subjects had a blood sample taken for serology to phase I and phase II antigens of C burnetii performed by indirect immunofluorescence assay. At each participating farm, seven to nine sheep had blood samples taken for C burnetii serology to be assessed by the complement fixation test. RESULTS The seroprevalence to C burnetii was higher in the group of shepherds (28.4%) than the control group (1.2%) (P<0.005). Among the group of shepherds, spending more than 5 h/week in the sheep barn (P=0.06) and buying and/or trading sheep within the past six months (P=0.004) were associated with positive C burnetii serology. A total of 137 of 334 sheep (41%) were seropositive for C burnetii. These positive sheep were distributed in 41 of the 46 flocks (89%). No correlation could be demonstrated between a serology for C burnetii in the herds and the shepherds. CONCLUSION Q fever is highly prevalent in the LSLRR of Quebec, affecting 89% of the flocks and 28% of the shepherds. Shepherds in this region are at increased risk for C burnetii infection in comparison to the general population.

Opinions of Quebec Parents and Vaccinators on the Usefulness of Chickenpox Vaccine

BACKGROUND A chickenpox vaccine was recently licensed in Canada. Because this vaccine has caused some controversy within the health care profession, studies among Quebec parents and vaccine providers were carried out, surveying their opinions concerning chickenpox vaccination. METHODS Three studies among parents of preadolescents, parents of two-year-old children completely or incompletely vaccinated and vaccinators were completed. The studies asked for opinions concerning the usefulness of vaccinating children against chickenpox. RESULTS The majority of parents of preadolescents (56%), and parents of two-year-old children completely (64%) and incompletely vaccinated (60%) favoured chickenpox vaccination. Among vaccinators, 53% of paediatricians, 37% of general practitioners and 33% of nurses considered universal vaccination of young children to be useful. A greater proportion of health care professionals were in favour of a policy of vaccinating groups at risk, such as susceptible adolescents (86%, 75% and 58%, respectively). There was a positive association between the perceived severity of chickenpox and the potential usefulness of the vaccine. CONCLUSION Quebec parents are more favourably disposed to chickenpox vaccine than vaccine providers. In contrast, strategies targeting susceptible groups would be generally well received by health care professionals. A considerable amount of work will be needed to convince vaccinators of the benefits of a universal childhood vaccination against chickenpox.

Long-term persistence of immunity after vaccination of pre-adolescents with low doses of a recombinant hepatitis B vaccine

Background and aims: Recent studies have shown no detectable antibodies and no response to a challenge dose of vaccine 10–20 y after receiving low doses (2.5–5 µg) of recombinant hepatitis B vaccine during first months of life. Little information is available on long-term persistence of immunity after vaccinating pre-adolescents with low doses of hepatitis B vaccine. Materials and Methods: This randomized trial was initiated in 1996 with the main objective to assess the persistence of antibodies and immune memory 5, 10 and 15 y after vaccinating 8–10 y-old children with three doses of Recombivax 2.5 µg, as well as the short and long-term effect of a booster dose given at different intervals. Results: The results of 560 subjects were included in this analysis. All subjects had a seroprotective antibody titer (≥ 10 IU/L) one month post-primary vaccination; 5, 10 and 15 y post-vaccination 95%, 95% and 87% had detectable antibodies, and 82%, 86%, and 68% had a seroprotective antibody titer; GMTs were 73 IU/L, 89 IU/L, and 28 IU/L, respectively. More than 99.4% of subjects had an anamnestic response to a challenge dose of vaccine given 5, 10, or 15 y post-vaccination. Five and ten years post-booster dose 97% and 95% of subjects still have a seroprotective anti-HBs titer with GMTs 16–18-fold higher when compared with those observed 5–10 y post-primary vaccination. Conclusions: Virtually all children vaccinated at the age of 8–10 y with low doses of hepatitis B vaccine still have an excellent immune memory up to age of 25 y. The results of this study do not support the use of booster doses.

New Era for Schools and Programs of Public Health in Canada

In Canada, in the last few years, there has been a very rapid expansion of programs and schools of public health in response to several crises or emergency situations. Provincial and national investigations convened after the Severe Acute Respiratory Syndrome outbreak in Toronto in 2003 underlined important deficiencies in the institutional capacity of the public health system and the need to develop training of public health professionals and managers on a large scale.

Antibody and immune memory persistence after vaccination of preadolescents with low doses of recombinant hepatitis B vaccine

Little is known about the impact of low-dose hepatitis B vaccine on the persistence of anti-HBs and immune memory in school-age children. Recombivax-HB 2.5µg (RB) has been widely used in school-age children. RB induces high seroprotection rates, but relatively low anti-HBs titers. The main objectives of this phase of the study were to assess anti-HBs persistence and the presence of immune memory 10 years post-vaccination of 8-10 year-old children with 3 doses of RB and the persistence of anti-HBs post-booster dose administration 5 (Group A; n=250) or 10 years (Group B; n=263) post-vaccination. No significant difference was observed between GMTs and the proportion of subjects with anti-HBs titers ≥10mIU/mL 5 or 10 years post-vaccination. In both groups, a 56-fold decrease of anti-HBs GMTs was observed. One month post-booster, all but two subjects in Group A had an anti-HBs titer ≥10mIU/mL. A 4.9- and 11.4-fold decrease in anti-HBs GMTs were observed during the first year post-booster in Group A and B, respectively. One year post-booster, the two groups were equivalent: ≥98.8% of subjects had an anti-HBs ≥10mIU/mL. In group A, five years post-booster, 96.8% had a titer ≥10mIU/mL; the GMT was 17-fold higher than the GMT 5 years post-vaccination (p

Preadolescent non- and hyporesponders following three doses of hepatitis B vaccine need only one more dose

A small proportion of healthy children fail to develop antibodies against hepatitis B after three doses of vaccine. Few data are available regarding the optimal re-immunization strategy. We measured the immune response 1 month after a single supplementary dose of recombinant hepatitis B vaccines in 18 young preadolescents who were non- or hyporesponsive after a regular primary course of three doses of recombinant hepatitis B vaccines. Among them, 100% seroconverted and 89% reached the seroprotective titer of 10 milli-International Units (mIU)/ml. Most healthy children, particularly if they are hyporesponders, will have reached the seroprotective level after one dose and will not need further injections.