Deadly hitchhiker threat to young
Researchers have warned of the risk of measles outbreaks among infants, adolescents and young adults because of gaps in the nation’s immunisation coverage against the potentially deadly disease.
While the World Health Organisation has declared Australia measles-free, infectious disease experts have cautioned parents and health authorities that they need to remain vigilant about maintaining high rates of vaccination because of the vulnerability of young people no longer exposed to wild versions of the infection.
A study in the Health Department’s latest Communicable Diseases Intelligence report found the incidence of measles plummeted following the commencement of mass vaccination programs in the 1980s and 1990s, and was now at a level “consistent with elimination of indigenous measles in the country”.
Since the last big outbreak in the early 1990s, when almost 10,000 people caught the disease and four died, the rate of infection has plunged. Between 2000 and 2011, 990 cases were notified but none were fatal.
However, although the disease is no longer considered to be endemic, it is still being brought into the country by people travelling from regions where it is common, raising the risk of infection for vulnerable groups, particularly the very young.
Children are not eligible for their first measles vaccine until they are 12 months, and national figures for 2000 to 2011 show the incidence of the disease was highest in this age group, reaching a peak of 3.8 per 100,000 in 2011.
Next most vulnerable were children aged between one and four years, followed by adolescents aged 10 to 19 years and young adults aged 20 to 34 years.
The authors of the study, who were from the Health Department, the National Centre for Immunisation Research and Surveillance and the Australian National University, speculated that infants could be particularly vulnerable because of a decline in maternal antibodies in women with vaccine-acquired immunity.
“It has been postulated that because measles is becoming rare, the lack of natural boosting thorough exposure to wild virus in both vaccinated women and women with past infection has consequently resulted in infants becoming more susceptible,” they wrote. “It is therefore important…that timely vaccine uptake among infants occurs at the recommended 12 months of age.”
They also highlighted gaps in coverage caused by the staggered introduction of mass vaccination programs in the 1980s and 1990s.
In particular, they noted that those born between 1968 and 1982 were “particularly susceptible as low vaccine coverage existed when they were infants and circulation of wild virus was becoming less common”. In addition, people in this age group missed out on a second round of vaccinations for adolescents carried out between 1994 and 1998, while a 2001 immunisation campaign aimed at reaching many of them had only limited success.
The researchers said there was a risk of under- or un-vaccinated young adults catching the disease while travelling overseas, and urged greater efforts to assess their immunity before they left the country.
“As most outbreak in Australia begin with an importation of measles from an endemic country, it is essential that measles immunity status be assessed when patients attend clinics to receive vaccinations for international travel,” they said, citing research showing that just 4 per cent of travellers who attended hospital within two years of returning from abroad were vaccinated against measles, mumps and rubella.
“Clearly, age-specific vulnerability of populations exist[s], even though measles is so rare in Australia and, consequently, this may lead to outbreaks in these populations,” the authors said. “Hence, there is an ongoing need to improve vaccine uptake in vulnerable populations.”