Efficacy of an acellular pertussis vaccine in Japan

Control selection and confounding factors: A lesson from a Japanese case-control study to examine acellular pertussis vaccine effectiveness

When using a case-control study design to examine vaccine effectiveness, both the selection of control subjects and the consideration of potential confounders must be the important issues to ensure accurate results. In this report, we described our experience from a case-control study conducted to evaluate the effectiveness of acellular pertussis vaccine combined with diphtheria-tetanus toxoids (DTaP vaccine). Newly diagnosed pertussis cases and age- and sex-matched friend-controls were enrolled, and the history of DTaP vaccination was compared between groups. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) of vaccination for development of pertussis. After adjustment for potential confounders, four doses of DTaP vaccination showed a lower OR for pediatrician-diagnosed pertussis (OR=0.11, 95% CI, 0.01-0.99). In addition, the decreasing OR of four doses vaccination was more pronounced for laboratory-confirmed pertussis (OR=0.07, 95%CI, 0.01-0.82). Besides, positive association with pertussis was observed in subjects with a history of steroid treatment (OR=5.67) and those with a recent contact with a lasting cough (OR=4.12). When using a case-control study to evaluate the effectiveness of vaccines, particularly those for uncommon infectious diseases such as pertussis, the use of friend-controls may be optimal due to the fact that they shared a similar experience for exposure to the pathogen as the cases. In addition, to assess vaccine effectiveness as accurately as possible, the effects of confounding should be adequately controlled with a matching or analysis technique.

Using age-stratified incidence data to examine the transmission consequences of pertussis vaccination

Pertussis is a highly infectious respiratory disease that has been on the rise in many countries worldwide over the past several years. The drivers of this increase in pertussis incidence remain hotly debated, with a central and long-standing hypothesis that questions the ability of vaccines to eliminate pertussis transmission rather than simply modulate the severity of disease. In this paper, we present age-structured case notification data from all provinces of Thailand between 1981 and 2014, a period during which vaccine uptake rose substantially, permitting an evaluation of the transmission impacts of vaccination. Our analyses demonstrate decreases in incidence across all ages with increased vaccine uptake - an observation that is at odds with pertussis case notification data in a number of other countries. To explore whether these observations are consistent with a rise in herd immunity and a reduction in bacterial transmission, we analyze an age-structured model that incorporates contrasting hypotheses concerning the immunological and transmission consequences of vaccines. Our results lead us to conclude that the most parsimonious explanation for the combined reduction in incidence and the shift to older age groups in the Thailand data is vaccine-induced herd immunity.

Acellular pertussis vaccines in Japan: past, present and future

An antivaccine movement developed in Japan as a consequence of increasing numbers of adverse reactions to whole-cell pertussis vaccines in the mid-1970s. After two infants died within 24 h of the vaccination from 1974 to 1975, the Japanese government temporarily suspended vaccinations. Subsequently, the public and the government witnessed the re-emergence of whooping cough, with 41 deaths in 1979. This series of unfortunate events revealed to the public that the vaccine had, in fact, been beneficial. Furthermore, researchers and the Japanese government proceeded to develop safer pertussis vaccines. Japan now has the most experience worldwide with acellular pertussis vaccines, being the first country to have approved their use. This review describes the major events associated with the Japanese vaccination program. The Japanese experience should be valuable to other countries that are considering the development and use of such vaccines.

Factors influencing the spread of pertussis in households

The objective of this study was to compare the spread of pertussis in children and adults being secondary contacts after household exposure. The study was nested in an efficacy trial of an acellular pertussis vaccine. The spread of the disease was also monitored with respect to gender and antibiotic therapy. A total of 453 index cases, of which 133 were monitored for adult disease, fulfilled the WHO definition of pertussis. They had contacts to 173 unvaccinated children aged 6-47 months, and a total of 101 adults with pertussis were followed. Detection of the bacteria, or a significant increase of specific antibodies confirmed the diagnosis. Secondary spread of the disease was assumed, when a household member coughed for 7 days or more and had laboratory evidence for pertussis. Crude attack rates (AR) were 69% in children and 31% in adults (P < 0.05). AR in children were independent of gender but more women than men (P=0.02) were affected in those households where the index case was a child. Erythromycin treatment of the index case reduced the AR in exposed toddlers from 80% to 57% (P=0.06), and in exposed adults from 40% to 21% (P=0.2). Erythromycin therapy in contacts did not alter the clinical course of the disease significantly.

CONCLUSIONS

In a household study of pertussis, 69% of children and 31% of adults (more women than men) contracted the disease. Erythromycin reduced the number of infections in household contacts, but did not alter the clinical course in those who contracted pertussis.

Randomized controlled trial of acellular diphtheria, pertussis and tetanus vaccines in southern Ghana

A randomized controlled trial of acellular diphtheria/pertussis/tetanus (ADPT) freeze-dried and liquid vaccines in infants was conducted in a peri-urban community (Ashaiman) in southern Ghana. Immunogenicity of the acellular vaccines, persistence of antibodies and adverse reactions were compared with those achieved with a whole-cell diphtheria-pertussis-tetanus (DPT) vaccine. The incidence of pertussis in the vaccine groups and prevalence of pertussis in children under 5 years of age in the study area were also determined. The acellular vaccines produced significantly fewer local and systemic reactions. Local reactions such as swelling and redness were observed in 2% (8/399) to 2.3% (9/385) of the acellular vaccine recipients as against 31% (122/394) in the whole-cell vaccine group. Fever ( > or = 37.5 degrees C) occurred in 7.27% (29/399) to 9.8% (38/385) in the acellular vaccine groups compared with 36.6% (145/394) in the whole-cell vaccine group. Geometric mean titres (GMTs), measured by ELISA, to pertussis toxin (PT) and filamentous haemagglutinin (FHA) were significantly higher in the acellular vaccine groups than in the whole-cell DPT (WCDPT) group. There were no significant differences in the GMTs of tetanus and diphtheria antitoxins between the two groups after each vaccination. Twelve months after primary vaccination, GMTs to PT in the freeze-dried, liquid ADPT groups and the WCDPT group have fallen from 56.23, 62.63 and 44.97 ELISA U/ml to 6.08, 6.18 and 11.30 ELISA U/ml, respectively. GMTs to FHA in all the vaccine groups also dropped during the same period from 49.94, 41.73 and 20.74 ELISA U/ml to 7.26, 7.72 and 5.91 ELISA U/ml, respectively. In this comparative controlled trial, the ADPT vaccines were more immunogenic, with less local and systemic reactions, than the WCDPT vaccine but there was a considerable drop in antibody titres in all the vaccine groups 12 months after primary vaccination. However, the levels of titres of anti-PT and anti-FHA antibodies in all the three vaccines that confer protection are not known. Further studies are necessary to provide this information in order to assess the need for subsequent booster doses after primary immunization with both ADPT and WCDPT vaccines.

Long-term human serum antibody responses after immunization with whole-cell pertussis vaccine in France

Three hundred sixty children were tested for pertussis serology 0.5 to 1.58 months after complete whole-cell pertussis vaccination. An immunoblot assay was used to detect serum antibodies to pertussis toxin, filamentous hemagglutinin, adenylate cyclase-hemolysin, and pertactin, and agglutination was used for detection of anti-agglutinogen antibodies. Antibodies against pertussis toxin, pertactin, and agglutinogens decreased rapidly after vaccination but increased secondarily, suggesting exposure to infected persons. In contrast, anti-filamentous hemagglutinin antibodies persisted and anti-adenylate cyclase-hemolysin antibodies increased continuously, suggesting either cross-reaction with non-Bordetella antigens or exposure to Bordetella isolates expressing these two antigens, including Bordetella pertussis. These data suggest that unrecognized pertussis is common in France despite massive and sustained immunization in infants and that vaccinated children become susceptible to infection more than 6 years after their last vaccination.

Pertussis immunization with acellular vaccines in Ghanaian children

In the present study, the persistence of antibodies to pertussis antigens was assessed in 51 Ghanaian children immunized with one of two acellular vaccines and one whole cell vaccine in early infancy. The effect of a booster dose 1 year after primary immunization was also examined. Antibody titres to pertussis toxin (PT) and filamentous haemagglutinin (FHA) were measured 1 month and 1 year after primary immunization and 1 month after the booster dose. Although geometric titres (GMTs) to FHA were significantly higher in the two types of acellular vaccinees in the whole cell vaccinees 1 month after primary immunization, GMTs to FHA and PT after 1 year were not significantly different in the three groups. Geometric mean titres to PT and FHA following the booster dose were significantly higher in the acellular vaccinees than in the whole cell vaccinees. Seropositivity rates to PT and FHA in the acellular vaccinees, which were more than 93.3% 1 month after primary immunization, ranged from 50.0 to 77.8% after 1 year. In conclusion, the acellular vaccines did not produce higher antibody levels than the whole cell vaccine 1 year after primary immunization. The booster dose was essential to maintaining sufficient seropositivity to pertussis antigens.

Sample size requirements for stratified prospective studies with null hypothesis of non-unity relative risk using the score test

The standard test of the null hypothesis of unity of the relative risk seeks to determine if two treatments differ. It does not apply when the requirement is either to establish the equivalence of two treatments or to determine whether the relative risk is less than a specified value other than one. This paper presents the asymptotic power function of the score test for the null hypothesis of a specified value of a common relative risk for stratified prospective studies and proposes an approximate formula for the sample size required for a specific power of the test. One can obtain a sample size formula for stratified studies with the standard null hypothesis of unity relative risk as a special case of this formula.

A randomized controlled trial of two acellular pertussis-diphtheria-tetanus vaccines in primary immunization in Ghana: antibody responses and adverse reactions

Two acellular pertussis vaccines combined with diphtheria and tetanus toxoids (APDT vaccines) were compared with a whole cell PDT (WCPDT) vaccine in primary immunization in Ghana. One is a liquid vaccine which is used for general immunization in Japan and the other is a freeze-dried vaccine newly developed as a heat-stable vaccine. Eighty-nine infants were recruited in the study. Sixty-eight who completed three doses of the immunization were assessed for immunological responses. Twenty-one dropped out because of sickness or moving from the study area. A total of 242 vaccinations in 89 infants were followed up for adverse reactions. Geometric mean titres (GMTs) to filamentous haemagglutinin in the two APDT vaccinees were significantly higher than in the WCPDT recipients. GMTs to pertussis toxin, diphtheria and tetanus toxoids were not significantly different among the three groups. Seropositive rates to pertussis antigens, tetanus and diphtheria toxoids were 94.4 to 100% in the two APDT vaccines. Systemic reactions within 7 days of inoculation were similarly low in the three groups, but significantly fewer infants had local reactions after either of the two APDT vaccines than after the WCPDT vaccine.

Quantification of pertussis toxin, filamentous haemagglutinin, 69 kDa outer membrane protein, agglutinogens 2 and 3 and lipopolysaccharide in the Danish whole-cell pertussis vaccine

The amounts of pertussis toxin (PT), filamentous haemagglutinin (FHA), 69 kDa outer membrane protein (69 kDa OMP) and agglutinogens (AGG) 2 and 3 in extracts from the Danish whole-cell pertussis vaccine were studied in quantitative capture ELISA. With the exception of PT, the most effective extraction of these antigens was by heating the bacteria at 60 degrees C for 30 min in 2 M urea followed by sonication for 45 s. Extraction by 1 M sodium chloride prior to sonication resulted in higher levels of antigenic and biologically active PT. On average, a single human dose of pertussis vaccine (approximately 16 opacity units) was found to contain 5520 ng FHA, 63 ng PT, 1061 ng 69 kDa OMP, 397 ng AGG 2, 534 ng AGG 3 and 4840 ng lipopolysaccharide (LPS). The antigen content of one dose of the Danish pertussis vaccine appears to be low compared with the amounts found in the acellular vaccines currently in use. These findings may have important implications for the evaluation of the protective substances and the immunogenicity of whole-cell as opposed to acellular pertussis vaccines.

Comparison of acellular (B type) and whole-cell pertussis-component diphtheria-tetanus-pertussis vaccines as the first booster immunization in 15- to 24-month-old children

We compared an acellular (B type) pertussis-component diphtheria-tetanus-pertussis (DTP-Ac) vaccine containing equal amounts of filamentous hemagglutinin and lymphocytosis-promoting factor with a conventional whole-cell vaccine as the first booster immunization in 162 healthy children 15 to 24 months of age. Fewer local reactions (e.g., erythema, swelling, and tenderness at the injection site) were seen in DTP-Ac vaccine recipients during the first 48 hours of observation. This group also had fewer episodes of fever (> or = 38 degrees C) and other systemic reactions (e.g., irritability, drowsiness, and anorexia). Overall, 57% of the DTP-Ac vaccine recipients had no obvious adverse reactions, in contrast to 5% in the comparison group. At 4 to 8 weeks after vaccination, serum antibody responses to filamentous hemagglutinin and lymphocytosis-promoting factor were greater in recipients of the acellular vaccine as determined by an enzyme-linked immunosorbent assay. We conclude that this B-type acellular vaccine is both immunogenic and much less likely to cause an adverse reaction than a currently licensed whole-cell vaccine, and is suitable for routine booster immunizing doses to protect against pertussis.

The cell mediated and humoral immune response to vaccination with acellular and whole cell pertussis vaccine in adult humans

The cell mediated immune response (CMI) against pertussis antigens following vaccination with the traditional Danish whole cell pertussis vaccine (WC-P) and the Japanese acellular pertussis vaccine (A-PV) JNIH-3 was studied in four adult human volunteers. Vaccination with the A-PV induced an in vitro proliferative response of peripheral blood lymphocytes to pertussis toxin (PT) subunits S2-S4, S3-S4 and S5 and the filamentous hemagglutinin (FHA), and a better serological response to native PT, detoxified PT (dPT) and FHA than the WC-PV. The induced CMI and serological response were followed over a period of 17 weeks, and were not seen to decline during this period. Further, an in vitro proliferative response to Bordetella pertussis agglutinogen 2 and 3 were demonstrated using lymphocytes from recently and not-so-recently pertussis-vaccinated adults.

Immunogenicity and protective efficacy of pertussis toxin subunit S1 produced by Bacillus subtilis

Pertussis toxin (PT) subunit S1 was produced in Bacillus subtilis as a secretory protein designated BacS1. BacS1 was partially purified and used to immunize mice. The sera were tested for PT-neutralizing antibodies and for protective capacity in a mouse model. Unlike previous findings with recombinant S1 from Escherichia coli, the recombinant BacS1 protein induced antibodies that were both neutralizing and protective. An adjuvant was necessary for efficient immunization with BacS1 but not with PT. Of the four adjuvants tested, aluminium phosphate gel was insufficient whereas Freund's incomplete adjuvant, Klebsiella lipopolysaccharide and Ribi's monophosphoryl lipid A-trehalose dimycolate emulsion all resulted in protective antibody production in NIH mice.

Production and secretion of pertussis toxin subunits in Bacillus subtilis

Pertussis toxin (PT) is a major component of today's acellular whooping cough vaccines. The use of acellular vaccines is predicted to increase sharply in the near future. There is therefore a need to produce PT in a way that makes its purification as easy as possible. Our approach was to express all five PT subunits individually in Bacillus subtilis. We have used vectors containing the promoter and signal sequences of the alpha-amylase gene of Bacillus amyloliquefaciens followed by an insert encoding the appropriate PT-subunit. All PT-subunits were secreted and found in the culture supernatant. The level of expression varied considerably: S1 and S5 were produced in large quantities whereas much smaller amounts of S2, S3 and S4 were found. The subunits were also present in the membrane fraction of the respective strains.

Protection against pertussis by acellular pertussis vaccines (Takeda, Japan): household contact studies in Kawasaki City, Japan

To evaluate the vaccine efficacy of an acellular pertussis vaccine which has been in clinical use in Japan since 1981, a retrospective study was performed by a questionnaire survey of secondary pertussis attacks through family contact in 146 children with pertussis diagnosed in the period from January 1981 through May 1988. In this study, acellular vaccine made by Takeda Pharmaceutical Company, which contains a high level of FHA (filamentous hemagglutinin), a low level of PT (pertussis toxin) and a small amount of agglutinogen, was evaluated. Secondary pertussis attacks through family contact were found in 17 of 29 siblings (58.6%) not immunized with pertussis vaccine. On the other hand, 27 siblings immunized with Takeda's acellular vaccine were exposed to pertussis through family contact and a secondary attack was seen in only one of them (3.7%). The present study revealed an efficacy rate of 93.7% for Takeda's acellular pertussis vaccine.

Clinical, metabolic, and antibody responses of adult volunteers to an investigational vaccine composed of pertussis toxin inactivated by hydrogen peroxide

A toxoid vaccine, composed of purified pertussis toxin inactivated with H2O2 (NICHD-Ptxd), was developed on the basis of evidence that serum neutralizing antibodies (antitoxin) would confer immunity to pertussis. In vivo and in vitro assays of NICHD-Ptxd showed only trace or nondetectable levels of pyrogenic, adenosine diphosphate-ribosyltransferase, binding and pharmacologic activities. Nevertheless, about 40% of the antigenicity of pertussis toxin was retained. Adult volunteers were injected, two times 6 weeks apart, with either 10 (n = 21), 50 (n = 25), or 75 (n = 30) micrograms/dose of one lot, Ptx-06, adsorbed onto AI(OH)3. Neither fever nor changes in the levels of leukocytes, lymphocytes, fasting blood glucose, or insulin were observed in the volunteers. The optimal immunizing dose, 50 micrograms, induced levels of antitoxin (geometric mean (GM) 302 U) comparable to those found in eight adults convalescent from pertussis (GM 269 U) and greater than those found in 18-month-old children after their fourth dose of diphtheria and tetanus toxoids and pertussis vaccine (GM 20.0 U, p less than 0.001). These data indicate that NICHD-Ptxd is safe and immunogenic in adults, and they justify its evaluation in infants and children.

Pertussis toxin S1 mutant with reduced enzyme activity and a conserved protective epitope

Pertussis toxin (PTX) is a major virulence factor in whooping cough and can elicit protective antibodies. Amino acid residues 8 to 15 of PTX subunit S1 are important for the adenosine diphosphate-ribosyltransferase activity associated with the pathobiological effects of PTX. Furthermore, this region contains at least a portion of an epitope that elicits both toxin-neutralizing and protective antibody responses in mice. The gene encoding the S1 subunit was subjected to site-specific mutagenesis in this critical region. A mutant containing a single amino acid substitution (Arg9----Lys) had reduced enzymatic activity (approximately 0.02% of control) while retaining the protective epitope. This analog S1 molecule may provide the basis for a genetically detoxified PTX with potential for use as a component of an acellular vaccine against whooping cough.

Protective effect of acellular pertussis vaccines

Two acellular pertussis vaccines, a mono-component toxoid of pertussis toxin and a two-component vaccine containing both the toxoid and filamentous haemagglutinin, were used for primary immunization of infants 5 1/2 to 10 months of age in two clinical trials in Sweden. Over a follow-up period of 12 to 17 months, 37 children were exposed to pertussis in the household or a daycare centre. Only one child developed mild, culture-confirmed pertussis as opposed to the expected number of 30 to 33 cases based on an assumed attack rate of 80-90% in non-immunized children. These preliminary findings indicate that, given as primary immunization to infants, the vaccines provide protection against pertussis.

Epidemiology and control of pertussis

An estimated 60 million children suffer from whooping cough annually, causing half a million deaths.

The gradual decline in incidence rates observed in Europe and North America even before the introduction of pertussis immunization is not likely to occur within the near future in developing countries short of widespread immunization efforts.

The present pertussis vaccine is effective, and serious adverse effects are rare in comparison with the consequences of the disease itself. A new, acel-lular vaccine is under trial and holds promise for the future.

Epidemiological studies and surveillance for pertussis activity are hampered by the fact that the clinical diagnosis is difficult to make under field conditions. New serological techniques may bring improvement in this respect.

Immunization does not play a significant role in outbreak control. Outbreak investigations are, however, extremely valuable for assessment of the effectiveness of immunization programmes; they provide valuable information, not easily obtained by other means, on age-specific attack rates and vaccine efficacy if the immunization status of the population is known.

Acellular pertussis vaccine in adults: adverse reactions and immune response

An acellular pertussis vaccine JNIH-6 containing pertussis toxin and filamentous hemagglutinin was evaluated in adult volunteers with regard to adverse reactions and antibody response. Adverse reactions were few and mild. A late onset local reaction was seen in 22 of the 47 vaccinees (47%) as compared to none of the 20 subjects receiving a placebo, the carrier solution of aluminium phosphate of the vaccine. The reaction, which manifested itself on the 6th to 8th day after vaccination, consisted in all cases of an induration and/or swelling considered insignificant by the majority of the subjects. The reaction was only found in vaccinees receiving a first dose of vaccine and was independent of the prevaccination antitoxin level. The vaccine induced a highly satisfactory antibody response to both filamentous hemagglutinin and pertussis toxin.

Adverse reactions and antibody responses to acellular pertussis vaccine

Two types of acellular pertussis vaccine are used in Japan: the filamentous hemagglutinin (F-HA) predominant type and the pertussis toxin (PT)-F-HA type. We tested one lot of vaccine from each of three manufacturers (lots A and B, F-HA predominant type; lot C, PT-F-HA type). One hundred fifteen healthy children between the ages of 3 months and 23 months were immunized with one of the three lots of acellular pertussis vaccine to assess adverse reactions and antibody responses. The incidence of fever (temperature greater than or equal to 38 degrees C) was 2.6% for lot A, 1.2% for lot B, and 2.5% for lot C. The incidence of local reactions greater than 5 cm in diameter was 1.9% for lot A, 2.4% for lot B, and 3.3% for lot C. Thus no significant differences in adverse reaction were observed. The anti-PT antibody responses in the tested vaccines were equal to or greater than those in patients with pertussis in the convalescent stage, and the anti-F-HA antibody responses were far higher than those of convalescing patients. Lot C produced the highest anti-PT antibody, and Lot A the highest anti-F-HA antibody.