Tetanus and Diphtheria Immunity Low in Older Australians
Diphtheria and tetanus have been well controlled in Australia since routine childhood vaccination began in the 1950s but older Australians may not be so well protected according to research published in the current issue of the Medical Journal of Australia.
The results of the first national serosurvey of immunity to tetanus and diphtheria in Australians show that while almost 100 per cent of children aged between five and nine are immune or partially immune to tetanus and diphtheria, less than 60 per cent of people aged over 50 years are protected from diphtheria and less than 75 per cent from tetanus.
Heather Gidding, Epidemiologist at the Centre for Infectious Diseases and Microbiology at Westmead Hospital, says the results show good uptake of diphtheria-tetanus-pertussis (DTP) vaccine as part of the childhood vaccination schedule, but additional efforts are needed to protect people over 50, especially travellers, who are most at-risk.
The research, which analysed 1950 samples of sera tested for diphtheria and 2884 for tetanus from July 1996 to May 1999, showed immunity declines with age, more so for diphtheria than for tetanus.
Men and women had similar diphtheria antitoxin levels, while women had lower levels of tetanus antitoxin compared with men of the same age. The difference was most marked in people aged 70 years and over, probably because of vaccination during military service in the Second World War.
Diphtheria spreads from person to person via the respiratory route or direct contact with infected sores. Tetanus usually results from contamination of a wound with soil containing spores of Clostridium tetani, but does not spread from person to person.
"There have been no reported cases of laryngeal diphtheria in Australia since 1991-92, when 23 cases and one death were reported in the Northern Territory, mainly in Aboriginal adults," Ms Gidding says.
"But a much larger outbreak of diphtheria in Russia between 1990 and 1997 of 140 000 cases and 4 000 deaths showed the potential for re-emergence of epidemic disease in inadequately immunised populations.
"In Australia there have been fewer than 10 notifications of tetanus per annum since 1995, but 20-40 recorded hospital admissions for tetanus and occasional deaths. The discrepancy probably represents failure of clinicians to notify some cases and incorrect classification or misdiagnosis of hospitalised cases.
Low immunity levels prompted calls for changes to the Australian Standard Vaccination Schedule in 2000.
"A booster dose of adult diphtheria/tetanus (dT) vaccine given at age 50 should eventually improve immunity in people now aged 20-49 years," Ms Gidding says.
"Immunity in young adults should improve with the introduction in 2003 of a national school-based program providing a booster dose of dT to 15-17 year olds, but further efforts are required to improve immunity in the high-risk group of people over 50 years.
"Maintaining high childhood vaccination rates is necessary to achieve herd immunity to diphtheria and to protect individuals against tetanus," she says.
The Medical Journal of Australia is a publication of the Australian Medical Association.
CONTACT Heather GIDDING (02) 9845 5973 or (02) 9799-0107/ 0408 227 133
Judith TOKLEY, AMA Public Affairs, 0408 824 306 / 02 6270 5471