Changes in age specific immunity to diphtheria in Poland in the past 40 years

Seroprevalence of an antibody against diphtheria, tetanus, and pertussis among the elderly in Khon Kaen, Thailand

BACKGROUND

Owing to a declining birth rate and longer lifespan, the number of elderly people (≥ 60 years) in Thailand has grown rapidly. However, the elderly are at significant risk of infectious diseases because they have never been immunized, because they have not been completely immunized, or because their immunity has waned. Immunity against infectious diseases in the elderly is an important means of controlling diseases in the community. Our objective was to evaluate the seroprotective rate against diphtheria, tetanus, and pertussis in the elderly Thai population.

METHODS

In total, 430 healthy individuals from the northeastern region of Thailand were enrolled in this study and stratified into five age groups: 60-65, 66-70, 71-75, 76-80, and > 80 years. Serum samples were collected and quantitatively analyzed for diphtheria, tetanus, and pertussis IgG antibody by using commercial ELISA kits. For anti-diphtheria toxoid and anti-tetanus toxoid ELISA, values < 0.01 IU/ml were interpreted as seronegative, and for anti-Bordetella pertussis toxin ELISA, values < 5 IU/ml were interpreted as seronegative; these definitions were in accord with previous studies.

RESULTS

For diphtheria toxoid Ab, the majority of the population had antibody levels > 0.01 IU/ml. For tetanus anti-toxoid Ab, the majority of the population had antibody levels of > 0.01 IU/ml, of which approximately 34% had durable antibody protection levels (DAPL) of ≥ 1 IU/ml. Meanwhile, nearly 45% of the population had an Ab level against pertussis lower than the protectivity level.

CONCLUSIONS

In total, 97.2%, 83.5%, and 55.8% of the population had a higher antibody level than the minimal protective level for diphtheria, tetanus, and pertussis, respectively. In order to prevent an outbreak of these diseases in the future, the elderly should be administered with Tdap revaccination to provide diphtheria herd immunity in the population; this will increase cocoon phenomenon for pertussis and protect the population from tetanus-prone injury.

Seroprevalence of Antibody Against Diphtheria Among the Population in Khon Kaen Province, Thailand

To assess diphtheria immunity in the northeastern region of Thailand, a seroepidemiological survey was undertaken in 2011 from 516 healthy individuals (age range 2-87 years) in Khon Kaen province. Diphtheria antitoxin levels were measured by enzyme-linked immunosorbent assay and titers of ≥0.1 IU/mL were considered to be protective antitoxin levels. Among the studied population, 94.8% have fully protective levels. The younger population (age range 2-19 years) has higher diphtheria immunity with seroprotection rates of 96.8% to 97.9%, compared with the adult population. The proportion of protective diphtheria antitoxin levels declines to 88.3% to 91.9% in the middle-aged group (20-50 years), and appeared to be higher again in the older age-group (50-70 years). To avoid epidemic spreading, promoting immunization booster programs will be helpful, especially among the adult population (20-50 years). Finally, this study may serve as a valuable guide in deciding exactly which age-groups should be targeted by such an effort.

The seroprevalence of diphtheria among adults in Izmir-Turkey

A serological survey to determine the immunity to diphtheria in the adult population in Izmir-Turkey was conducted according to the recommendations of the World Health Organization. A total of 339 blood samples were collected from subjects aged between 20 and 81, and diphtheria antitoxin levels were measured by the enzyme linked immunosorbent assay method. Titers below 0.1 IU/ml were considered to show insufficient immunity. Of the studied population, 56.3% had showed insufficient immunity against diphtheria. Diphtheria protection rates showed a gradual age-related decrease. The lowest immunity rate was observed in 40-49-year age group (30.6%) (p<0.05). There was no significant difference in the rate of immunity between subjects in terms of sex, levels of education, urban-rural region (p>0.05). These results emphasize the need for booster immunization of adults. The present vaccination policy should include re-vaccinations of the adult population every 10 years in order to provide a complete protection of the population.

Implications of the diphtheria epidemic in the Former Soviet Union for immunization programs

The massive diphtheria epidemic in the former Soviet Union provides important lessons for all diphtheria immunization programs: It is important to achieve a high level of childhood immunization, maintain immunity against diphtheria in older age groups, and use anti-epidemic measures, including immunization, to control epidemics in the early phase. The immunization coverage among children should be at least 90%. Further studies are needed to elaborate the most effective strategy to maintain immunity against diphtheria in adults (periodic booster doses, immunization of selected age groups in health care settings, use of Td [tetanus-diphtheria toxoids with reduced diphtheria toxoid content] vaccine instead of monovalent tetanus toxoid whenever tetanus toxoid is indicated [e.g., in treatment of wounds or in school-based immunization programs]). Efforts should be undertaken to monitor diphtheria immunity in different groups by conducting age-specific serologic studies.

Evaluation of the effectiveness of vaccination against diphtheria among medical staff of the chair and the Jagiellonian University Hospital of Infectious Diseases in Cracow, Poland. Some epidemiological observations

In Poland, twenty-five cases of diphtheria, mostly among adults (including five foreigners) in the region adjacent to the eastern border were registered in the years 1992-1996. In 1993-1994, because of the threat of diphtheria infection, 41 healthy members of the medical staff of the University Hospital of Infectious Diseases in Kraków, mainly women aged 25-57 years were immunized with Td and d vaccines with a 6-month interval between courses. Prior to vaccination, 17(41%) individuals showed a lack of diphtheria antibodies as determined with a passive haemagglutination test. 14 of them were aged 30-49 years. Six months after the 2nd dose of vaccine, all seronegative persons had developed a protective level of antibodies. Moreover, all vaccinated subjects showed a statistically significant increase of the antibody titre between the first and last serological examinations.