Dani Cohen

Double-blind vaccine-controlled randomised efficacy trial of an investigational Shigella sonnei conjugate vaccine in young adults

BACKGROUND The aim of this double-blind randomised vaccine-controlled trial was to assess the efficacy of a conjugate vaccine composed of Shigella sonnei O-specific polysaccharide bound to Pseudomonas aeruginosa recombinant exoprotein A (S sonnei-rEPA) and of an oral, live-attenuated Escherichia coli/S flexneri 2a (EcSf2a-2) hybrid vaccine among military recruits in Israel at high risk of exposure to Shigella spp. We report here our preliminary findings on the efficacy of S sonnei-rEPA; we have not documented sufficient cases to assess the efficacy of EcSf2a-2. METHODS Between April, 1993, and August, 1994, male Israeli Military recruits aged 18-22 years were asked to take part in our study. We enrolled 1446 soldiers from seven separate field sites (groups A-G). Soldiers were randomly allocated one injection of S sonnei-rEPA and four doses of oral placebo (n = 576), four oral doses of EcSf2a-2 and one injection of saline placebo (n = 580), or one injection of meningococcal tetravalent control vaccine and four doses of oral placebo (n = 290). Because there were no cases of S flexneri 2a, the EcSf2a-2 and meningococcal vaccines were the control group. We defined S sonnei shigellosis as diarrhoea with a positive faecal culture for S sonnei. Each group of soldiers was followed up for 2.5-7.0 months. The primary endpoint was protective efficacy of S sonnei-rEPA against S sonnei shigellosis. FINDINGS Cases of culture-proven S sonnei shigellosis occurred in four groups of soldiers (groups A-D), which comprised 787 volunteers (312 received S sonnei-rEPA, 316 received EcSf2a-2, and 159 received meningococcal control vaccine). In groups A-C, cases of shigellosis occurred 70-155 days after vaccination, whereas in group D cases occurred after 1-17 days. In groups A-C, the attack rate of shigellosis was 2.2% in recipients of S sonnei-rEPA compared with 8.6% in controls (protective efficacy 74% [95% CI 28-100], p = 0.006). S sonnei-rEPA also showed significant protection against shigellosis in group D (43% [4-82], p = 0.039). Prevaccination and postvaccination ELISA measurements of antibody to S sonnei lipopolysaccharide among recipients of S sonnei-rEPA showed that the vaccinees who developed S sonnei shigellosis had significantly lower serum IgG and IgA responses to the homologous lipopolysaccharide than those who did not (p = < 0.05). INTERPRETATION One injection of S sonnei-rEPA confers type-specific protection against S sonnei shigellosis. The high antibody concentration induced by the conjugate vaccine in volunteers who did not develop shigellosis suggests that there is an association between serum antibody titre and protection.

Reduction of transmission of shigellosis by control of houseflies (Musca domestica)

The effect of control of houseflies on the incidence of diarrhoea and shigellosis was evaluated in a prospective crossover intervention study at two military field bases several kilometers apart. In early summer, 1988, intensive fly control measures (mainly bait and trap strategy) were introduced on one base, while the other served as a control. After 11 weeks, as new cohorts arrived, the intervention was abruptly discontinued in the first base and instituted in the second for the next 11 weeks. The study was repeated the next summer. Overall, fly counts were 64% lower on the bases exposed to fly control measures (p = 0.024). Concomitantly, clinic visits dropped by 42% (p = 0.146) for diarrhoeal diseases and by 85% for shigellosis (p = 0.015), as did rates of seroconversion, by 76% (p = 0.024) for antibodies to Shigella and by 57% (p = 0.006) for antibodies to enterotoxigenic Escherichia coli. The findings indicate that houseflies, acting as mechanical vectors, transmit Shigella (and possibly enterotoxigenic E coli) diarrhoeal infections.

Age differences in immunity against wild and vaccine strains of poliovirus prior to the 1988 outbreak in Israel and response to booster immunization

During the 1988 type 1 polio outbreak in Israel, most cases occurred in previously vaccinated subjects aged 11-30 years, suggesting a possible age-related immunity deficit against the wild virus responsible for the outbreak. We examined type 1 poliovirus neutralizing antibody titres against the Sabin strain, the standard wild strain (Mahoney), the wild strain responsible for the 1988 outbreak and a previous wild strain from the region, on frozen sera drawn prior to the mass vaccination campaign from subjects aged 6 to 40 years. Response to vaccination with oral poliovaccine (OPV) was examined in a subgroup aged 18-40 years. At all ages, the highest antibody titres prior to the outbreak were against the Sabin strain. Geometric mean titres (GMTs) against both the Sabin strain and the wild Mahoney strain were significantly higher in the age groups 6-7, 12-13 and 30-40 years compared with the 18-29-year-olds. For the other wild strains, the GMT for those aged 30-40 years was significantly and substantially higher than in the other age groups, followed by the 12-13- and 6-7-year-olds and lowest in those aged 18-29 years. Following vaccination with OPV in subgroups aged 18-29 and 30-40 years, GMTs against Sabin and all wild strains were similar to each other and in both age groups. These findings suggest that there was a relative immunity gap against the wild type 1 strains in the age group that lacked prior exposure to wild virus and had received the last OPV dose more than 17 years previously.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term persistence of anti-diphtheria toxin antibodies among adults in Israel. Implications for vaccine policy.

Vaccination against diphtheria has essentially led to the disappearance of the disease in Israel. However, in other countries with high immunization coverage, isolated cases and small outbreaks have occurred in adults. Immunity following vaccination or natural exposure to toxigenic strains ofC. diphtheriae is conferred by serum antibodies to diphtheria toxin. Since booster doses of diphtheria toxoid are recommended every ten years in adults, this raises the question of persistence of protective levels Of anti-diphtheria toxin antibodies. In this study we assessed a possible age-related decline in anti-diphtheria toxin antibodies among adults in Israel. The study population comprised random samples in three age groups: 263 male recruits aged 18–19 years, 116 male reserve soldiers aged 25–35 years and 153 aged 41–51 years. Anti-diphtheria toxin antibody levels were measured by means of ELISA. Results indicate that 64.3% (95% CI=58.5–70.1%) of those aged 18–19 had anti-diphtheria toxin levels in excess of 0.1 IU ml−1, whereas the corresponding figures for ages 25–35 and 41–51 were 32.8% (95% CI=24.2–41.3%) and 15% (95% CI=9.4–20.7%). However, even in the oldest age group, 95.4% (95% CI=90.8–98.1%) had antibodies above the presumed protective level of 0.01 IU ml−1. Although these results indicate a significant age-related decline in anti-diphtheria toxin antibodies in vaccinated subjects, most had apparently protective levels. The absence of cases suggests that vaccine-induced immunity is long-lasting. However the immune status of the population should be carefully monitored.

Prevalence and correlates of diphtheria toxin antibodies among young adults in Israel

The paucity of information about immunity against diphtheria of young adults in Israel prompted us to analyse sera from a random sample of 480 recruits (263 males and 217 females) aged 18-19 years. Antitoxin antibody levels were determined by means of ELISA. Of the recruits 58.1% had antibody values greater than 0.1 IU/ml; 38.5% had amounts between 0.01 and 0.1 IU/ml, which is considered low when using the ELISA method, and 3.3% had less than 0.01 IU/ml. The results of this study suggest that a booster dose of antidiphtheria vaccine should be given to adults in Israel in order to ensure adequate antibody levels.

Prospective Cohort Studies of Shigellosis During Military Field Training

Abstract Epidemiological and clinical features of shigellosis occurring among cohorts of Israeli recruits followed-up for 3–6 months during the summer field training of years 1993–1997 were studied. The incidence rate of culture-proven shigellosis was the highest (78 cases per 1,000 recruits) in 1996 and the lowest (13 cases per 1,000 recruits) in 1995. Shigella sonnei (152 isolates) and Shigella flexneri (151 isolates) were the most common species. Fifty percent of the patients with shigellosis had fever (>37.5  °C), compared to only 18% of the subjects with other diarrheal diseases (P<0.001). The duration of illness was longer among subjects with shigellosis than among those with other diarrheal diseases (P<0.001). Illness due to Shigella flexneri was more severe than illness caused by Shigella sonnei.

Quantitative analysis of IgG class and subclass and IgA serum response to Shigella sonnei and Shigella flexneri 2a polysaccharides following vaccination with Shigella conjugate vaccines

It has been recently reported that a conjugate vaccine composed of the O-specific polysaccharide of S. sonnei bound to Pseudomonas aeruginosa recombinant exoprotein A (rEPA) conferred 74% protection against S. sonnei shigellosis. In the present study affinity purified Shigella antibodies were used as standards to quantify and characterize the serum antibody response to vaccination with Shigella sonnei or Shigella flexneri 2a polysaccharide conjugated to rEPA. The geometric mean concentrations of antibodies at the pre-vaccination stage were 3.8 microg/ml for IgG anti-S. sonnei LPS and 11.26 microg/ml for IgG anti-S. flexneri 2a LPS. Vaccination with S. sonnei-rEPA and S. flexneri 2a-rEPA induced the production of specific IgG antibodies to levels of 115.8 microg/ml and 126.5 microg/ml, respectively. The levels of specific antibodies above the pre-vaccination values persisted for at least 2 years. The IgG response to S. flexneri 2a-rEPA conjugate was almost entirely represented by the IgG2 subclass. The concentration of IgG1 anti-S. sonnei LPS was significantly higher than that of IgG2 14 days after vaccination with the homologous conjugate, but decreased to similar levels to those of IgG2 6, 12 and 24 months after immunization. Since the only difference between the S. sonnei and S. flexneri 2a conjugates lies in the different polysaccharides of the two Shigella serogroups (the protein rEPA, is identical in both cases), it follows that the different pattern of IgG subclass response is a result of the different structures of the two O-polysaccharides of S. sonnei and S. flexneri 2a.

Identification of Shigella species in stool specimens by DNA amplification of different loci of the Shigella virulence plasmid

The sensitivity and specificity of the polymerase chain reaction (PCR) for detection of DNA sequences specific toShigella spp. and enteroinvasiveEscherichia coli (EIEC) in stools was evaluated. Stool specimens were obtained from patients with acute gastroenteritis before and after antibiotic treatment. Fecal material was pre-incubated in phosphate-buffered saline, gram-negative broth or brain heart infusion (BHI) broth, and DNA was extracted and amplified. Primers complementary to theial or thevirF loci of the 140 MDa plasmid ofShigella were evaluated. The highest sensitivity for detection ofShigella DNA in stools (higher than that of culture) was reached by pre-incubation of the fecal material in BHI broth and use ofvirF primers for amplification. The specificity of this PCR protocol was documented by the negative results obtained with non-Shigella enteric organisms. These findings point out the important diagnostic and epidemiologic potential of thevirF-specific PCR protocol in the investigation ofShigella infections.

Norwalk Virus Gastroenteritis among Israeli Soldiers: Lack of Evidence for Flyborne Transmission

AbstractBackground: Paired sera collected from subjects before and after a fly-control intervention trial conducted in the Israel Defence Force (IDF) were tested for seroconversion to Norwalk virus (NV) to examine the role of NV as a cause of diarrhea in this population and to ascertain whether flies might also be implicated in transmission. Materials and Methods: An enzyme-linked immunosorbent assay (ELISA), using recombinant NV capsid proteins (rNV) as antigen was employed to determine the seroconversion rate in a sample of 444 subjects. Results: During 11-week field training cycles, 18% of IDF soldiers who were tested had an NV infection defined as a ≥ 4-fold rise in antibody, yielding a cumulative incidence of nearly one infection (0.95) per soldier per year. The rate of seroconversion was nearly twice as high among soldiers who recalled having diarrhea as among those who did not, but the rates did not differ significantly between soldiers in the fly intervention areas and those in the control areas. Conclusion: NV is a common cause of enteric infections and diarrhea among Israeli soldiers who serve under field conditions, but unlike infections with Shigella and enterotoxigenic Escherichia coli, transmission of NV cannt be interrupted with an aggressive program of fly-control.

Immunity to measles in young adults in Israel.

SummaryThe likelihood of an epidemic of measles in 1990–92 in Israel prompted us to study the immune status against measles in a random sample of 454 recruits aged 18–19 years in order to obtain data that might be used in determining vaccination policy. This cohort had received one dose of measles vaccine at 12 months of age. The measles immunity status was studied by determination of antibody values that were measured by means of an enzyme-linked immunosorbent (ELISA) IgG antibody test. Of the recruits, 84.6% were found to have positive sera for anti-measles IgG antibodies, while 13.7% had negative sera. Eight (1.7%) subjects had borderline results. The results of this study indicate the need to administer a second dose of measles vaccine at an older age in addition to the MMR (measles, mumps, rubella) vaccine that is now given in Israel at 12 months of age. This step will help achieve the World Health Organizations target of complete eradication of measles.ZusammenfassungDie Möglichkeit einer Masernepidemie in Israel in den Jahren 1990–92 veranlaßte eine Stichprobenuntersuchung, wobei 454 18- bis 19jährige Rekruten auf ihren Masernimmunstatus untersucht wurden. Die Daten sind für die weiteren Impfstrategien von grundlegender Bedeutung. Die untersuchte Gruppe hatte im Alter von 12 Monaten eine Dosis Masernimpfstoff erhalten. Der Masernimmunstatus wurde durch IgG-Antikörper mittels ELISA bestimmt. Bei 84,6% der Seren fanden sich positive, bei 13,7% negative und bei acht Fällen (1,7%) grenzwertige Testergebnisse. Aus diesen Ergebnissen ist abzuleiten, daß zusätzlich zu der nun in Israel eingesetzten MMR-Vakzine (Masern, Mumps, Röteln), die im Alter von 12 Monaten appliziert wird, eine Auffrischimpfung gegen Masern zu einem späteren Zeitpunkt erforderlich ist. Das Ziel der WHO, die Masern vollständig auszurotten, dürfte damit erreichbarer werden.