Diphtheria is an acute respiratory tract infection caused by diphtheria bacillus. It is clinically characterized by local grey and white pseudomembrane and systemic toxemia. Severe cases can be complicated with myocarditis and peripheral nerve palsy, with a case fatality rate of 10%. Diphtheria is mainly spread through respiratory droplets and can be transmitted by contacting contaminated utensils and food. Diphtheria can be divided into four types, the incidence of which is from high to low: pharyngeal diphtheria, laryngeal diphtheria, nasal diphtheria and other parts of diphtheria. Adults and older children are more likely to have pharyngeal diphtheria, while other types of diphtheria are more common in young children. Although diphtheria can be effectively controlled through vaccination, diphtheria outbreaks have occurred in some countries in recent years, especially in developing countries, and in two communities in South Africa in 2015, which suggests that diphtheria still poses a potential threat to human health.
In 1891, German bacteriologist Behring immunized sheep or goats with bacteria to obtain antiserum diphtheria antitoxin, which was successfully used for the first time to treat patients with diphtheria. In 1948, the diphtheria, tetanus and whole-cell pertussis combined vaccine (DTwP) came to market. Although DTwP has many advantages, its adverse reactions after inoculation have not been solved. In 1981, Japanese scientists took the lead in the development of a combined vaccine — diphtheria, tetanus and acellular pertussis combined vaccine(DTaP), which greatly reduced the adverse reactions after human inoculation. Human tests and serological effect have proved that DTaP was safe and effective for diphtheria prevention. In addition, the development of the diphtheria vaccine also shows us the difficulty in the design of therapeutic agents in clinical trials.
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Case Study
Patient enrollment is a key challenge for most clinical trials, especially in the study of vaccines to treat diphtheria. All children who were eligible for entry to the trial had completed their primary immunizations according to the UK schedule at the time of vaccination. These vaccines included three doses of diphtheria, whole cell pertussis, tetanus, Haemophilus influenzae type b and live attenuated oral polio (OPV), and children had to have them injected at least 3 years earlier (2.5 years earlier in the sub-study). However, children who met the requirements but had the following characteristics would be excluded: prior clinical or bacteriological diagnosis of diphtheria, pertussis, tetanus or poliomyelitis; immunosuppression; receipt of any vaccine in the previous 4 weeks or immunoglobulins within the previous 3 months; allergy to vaccine components; and parental refusal to consent to the study protocol including concomitant administration of the measles, mumps and rubella combined vaccine (MMR).
Statistical analysis is another challenge for the study. Demographic characteristics and baseline levels of anti-diphtheria and anti-tetanus toxoid antibodies were described for each group. The primary endpoint was the comparison of the percentage of subjects in each group between protective anti-diphtheria antitoxin levels ≥0.1 IU/ml and anti-tetanus antitoxin levels ≥0.1 EU/ml post-immunization. Groups were compared by estimated differences in the percentage exceeding these levels of antibodies, with 90% confidence interval (CI), an upper CI of less than 5% indicating non-inferiority, in line with the criteria of non-inferiority applied in this study.
For all other comparisons of proportions between groups Fisher’s exact test was used. Geometric mean titers (GMT) of anti-diphtheria, anti-tetanus, polio (types 1–3) and pertussis (PT, FHA, FIM and PRN) antibodies post-immunization were calculated with 95% confidence intervals by using t-tests. Analysis was repeated with rank-sum tests to assess the effect of the assumption of normally distributed data. These non-parametric analyses yielded similar results and only parametric results were presented here.
To investigate reactogenicity, local and systemic reactions occurring during the 7 days following vaccination were described. The proportion in each group reporting local (pain, erythema and swelling) or systemic (pyrexia, diarrhoea, rash, swollen joints, tiredness, vomiting) side effects was calculated and compared between groups by using Fisher’s exact test.
Using these criteria and the statistical strategy, we recruited appropriate patients and analyzed results from the study of a low-dose diphtheria, tetanus and acellular pertussis combination vaccine treatment in diphtheria.
Design:
The main study was an open, randomized and controlled phase II study. It focused on the immunogenicity and safety of combined adsorbed tetanus, low-dose diphtheria, five-component acellular pertussis and inactivated poliomyelitis vaccine (Td5aP-IPV) and combined adsorbed Td5aP-OPV, in comparison with combined adsorbed standard-dose diphtheria, tetanus, two-component acellular pertussis and inactivated poliomyelitis vaccine (DT2aP-IPV). And these vaccines were injected into healthy UK children who were priming themselves with DTwP vaccine at 2, 3 and 4 months of age at least 3 years before.
The sub-study was an open and uncontrolled phase IV study, which focused on the immunogenicity and safety of combined adsorbed Td5aP-IPV. And these vaccines were injected into healthy UK children who were priming themselves with diphtheria, tetanus and whole cell pertussis vaccine at 2, 3 and 4 months of age at least 2.5 years before.
They both included complete eligibility criteria, data collection schedule and detailed statistical analysis.
Participants:
The main study included children aged between 3.5 and 5, and children aged between 3 and 3.5 were only to participate in the sub-study. All recruited children should meet the requirements as follows:
- Children had completed their primary immunizations according to the UK schedule at the time of vaccination, which included three doses of diphtheria, tetanus, whole cell pertussis, Haemophilus influenzae type b and OPV, and these vaccines had to be injected at least 3 years earlier (2.5 years earlier in the sub-study);
- All children had received one dose of measles, mumps and rubella combined vaccine;
- In the main study, children had received a single dose of meningococcal serogroup C(Men C) conjugate vaccine as part of the nationwide ‘catch-up’ campaign;
- Only children who had been injected with three doses of Men C vaccine given concomitantly with the DTwP vaccine during infancy were eligible for the sub-study.
Length of enrollment period:
4-6 weeks
Interventions:
Children were allocated to receive one of the three vaccines described above by computer generated randomization, grouped in blocks of three. They were vaccinated intramuscularly into the deltoid muscle through a 16 mm, 25-gauge needle. The diphtheria containing the study vaccine was administered into the right deltoid while MMR into the left. Subjects were observed for 15–30 min after immunization for possible immediate adverse events. Parents were asked to complete a reactogenicity diary for 7 days following immunization. Blood samples were taken before vaccination and at the second visit 28–42 days later.
Main outcomes:
- Pre- and post-vaccination geometric mean titers and proportion with a protective antibody level for diphtheria;
- Local and systemic reactions in 1–7 days after vaccination.
Results:
Diphtheria antitoxin geometric mean titers were lower in the sera of children who received Td5aP-IPV when compared with those receiving Td5aP + OPV or DT2aP-IPV (Table 1). Local and systemic reactions were similar in the three groups except for a significant excess of local erythema and of rash in Td5aP + OPV compared to the control vaccine, DT2aP-IPV (Table 2).
Table 1. Pre- and post-vaccination geometric mean titers and proportion with a protective antibody level for diphtheria
Table 2. Local and systemic reactions 1–7 days post-vaccination
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References:
1. C.L. Collinsa, P. Salta, N. McCarthya, et al. (2004) 'Immunogenicity and safety of a low-dose diphtheria, tetanus and acellular pertussis combination vaccine with either inactivated or oral polio vaccine as a pre-school booster in UK children', Vaccine, 22(31):4262-4269.
2. ZHU Jian-qiong, WANG Ying. (2004) 'Serological Survey on the Effects of Two Kinds of Pertussis Diphtheria Tetanus Vaccines', Chinese Journal of Vaccines and Immunization, 10(2): 23-25.
3. Edmunds WJ, Pebody RG, Aggerback H, et al. (2000) 'The Sero-epidemiology of Diphtheria in Western Europe', Epidemiology and Infection, 125(1): 113-125.