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WHO currently recommends three vaccinations against hepatitis B to provide optimal protection against infection and carriage. However, immunological theory and mathematical modelling suggest that similar protection could be induced with two doses, and trials among adolescents and adults have shown comparable rates for both primary seroprotection and geometric mean titres following vaccination. We determined vaccine efficacy among 60 children who only received two doses of hepatitis B vaccine as infants and among 463 children who had received three doses after 4-7 years of follow-up. Vaccine efficacy among the two-dose group was 86.3% against anti-HBc positivity (infection) and 92.3% against HBsAg positivity (carriage), which was similar to the vaccine efficacy found among the participants who had received three doses. To confirm this comparable vaccine efficacy a randomised controlled non-inferiority trial with long-term follow-up is needed.

The study of cytotoxic T cell responses to measles antigens during infection and after vaccination may provide insight into the immunopathology of the infection. It will also provide a knowledge of the immunity conferred by wild or attenuated virus, which will help in the design of new vaccines. Direct cytotoxic T cell responses, which did not require in vitro restimulation, were measured from peripheral blood by a standard 51Cr-release assay in 35 patients with acute measles, using HLA class I matched allogeneic B cells as targets. 77% showed specific responses to measles fusion protein, 69% to the hemagglutinin, and 50% to the nucleoprotein. These responses, which were related to severity of disease and history of previous vaccination, had waned by 14-24 wk after measles when memory responses to the same antigens could be elicited by restimulation in 71% of the 13 patients tested. A similar pattern followed vaccination: direct cytotoxic responses to fusion and hemagglutinin proteins were shown in 70% of the 20 children tested while 50% responded to the nucleoprotein. These responses, which were mediated by both CD8(+) and CD4(+) cells, faded over 6 wk when memory responses could be restimulated. Thus, a vigorous cytotoxic T lymphocyte response to fusion, hemagglutinin, and nucleoproteins is important in both natural and vaccine-induced immunity to measles.

Because of the high prevalence of hepatitis B virus (HBV) infection in The Gambia, HBV vaccination has been incorporated into the national expanded programme on immunisation. We have assessed the efficacy of the vaccine against HBV infection and chronic carriage by examining 720 3-4-year-old children who had received the vaccine in infancy and 816 who had not received it. The vaccine was 84% (95% CI 78-89%) effective against infection and 94% (84-98%) effective against chronic carriage. Vaccinated infants of mothers positive for hepatitis B surface and e antigens were at greater risk of breakthrough infection and chronic carriage than infants of uninfected mothers. The high vaccine efficacy against the HBV carrier state, the main risk factor for the development of chronic liver disease and liver cancer, offers hope that the prevalence of these diseases may be reduced in the future.

358 children in the Gambian villages of Keneba and Manduar, where hepatitis B virus (HBV) infection is endemic, were vaccinated with plasma-derived vaccine against HBV according to one of four regimens and followed for up to 4 years. Two regimens by which vaccine was injected intradermally into children between 0 and 4 years old led to peak geometric mean (95% CI) concentrations of antibody against HBV surface antigen of 270 (202-358) and 555 (418-748) mlU/ml. The third regimen--intramuscular vaccination of children aged between 0 and 4 years--gave geometric mean peak antibody concentrations of 926 (765-1122) mlU/ml. A fourth regimen was intramuscular vaccination of children between 1 and 9 months old, which gave geometric mean antibody concentrations of 5431 (3903-75,456) mlU/ml. Despite these widely divergent responses and a 89% decay in antibody over the first 2 years, vaccination against HBV was 97% effective in preventing chronic infection. Vaccination was less effective in preventing uncomplicated infection: 5.3% of 264 vaccinees in Keneba and 19.1% of 94 vaccinees in Manduar tested positive for antibody to HBV core antigen. These "breakthrough infections" did not differ in frequency between regimens, and were associated with low initial antibody responses and chronic maternal carriage of HBV.

Sera were obtained from 119 Nigerian villagers two years after immunization with group A and group C meningococcal polysaccharide vaccines. Measurement of meningococcal antibody levels in individual serum samples by the haemagglutination technique showed that two years after vaccination the mean group A meningococcal antibody level was no higher in immunized subjects than in 140 age-matched, non-immunized controls. Over-all the mean group C meningococcal haemagglutinating antibody level was significantly higher in immunized subjects than it was in controls but this difference was not found in those under the age of 15 years at the time of vaccination. However, when pooled serum samples from the same subjects were tested for meningococcal antibodies by radioimmunoassay, immunized subjects were found to have significantly higher mean levels of both group A and group C meningococcal antibodies than the controls. The possible reasons for this discrepancy are considered and the significance of these findings in relation to plans for mass immunization with meningococcal vaccines in tropical Africa are discussed.

Household contacts of patients with group A meningococcal infection were vaccinated with either meningococcal vaccine or tetanus toxoid. Five of the 523 subjects who received tetanus toxoid developed meningococcal meningitis and another four probably had meningococcal disease. Only one possible case of meningococcal infection occurred among 520 contacts vaccinated with meningococcal vaccine. Vaccination had no effect on nasopharyngeal carriage of meningococci. Vaccination of household contacts of patients with group A meningococcal infections is an effective way of using limited supplies of meningococcal vaccine, though its value would be limited in an epidemic. Secondary cases of meningococcal infection often occur within a few days of the index case, and, although vaccine alone seemed to provide adequate prophylaxis in these Nigerian subjects, additional chemoprophylaxis may be needed to cover this critical period.

A combined group A and group C meningococcal polysaccharide vaccine was given to 438 Nigerian schoolboys shortly before an outbreak of group A meningococcal disease occurred in their school. Four months after vaccination the carriage rate of group A meningococci among vaccinated subjects (11%) was no different from that found among the controls (12%), although a good antibody response to both components of the vaccine was observed. One case of group A meningococcal disease was recorded amongst 438 vaccinated subjects while five cases occurred among 874 controls.

Three trials of intradermal hepatitis B virus (HBV) vaccines were made in Gambian children. In the first trial HBV vaccine (1 microgram) was given to neonates in the same syringe with BCG followed by two further does of 1.0 microgram of intradermal HBV vaccine. The trial was a failure, for 19 of 32 subjects had an HBV surface antibody response of less than 10 m.i.u./ml. In the second trial in young children two different regimes were used: two doses of 2 micrograms HBV vaccine were given intradermally after a 20 micrograms intramuscular dose or three doses of 2 micrograms were given intradermally. In both cases geometric mean antibody responses were significantly lower than in the control group who were given 20 micrograms HBV intramuscularly followed by two 10 micrograms doses intramuscularly. Vaccine failures, defined as the presence of HBV surface antigen or core antibody or absence of surface antibody, were also significantly higher in the intradermal groups. In the third trial 4 micrograms of vaccine were given intradermally to 20 young children with a multiple orifice head fired by a jet gun: all had a good HBV surface antibody response of greater than 100 m.i.u./ml of serum.