Australia has one of the highest measles vaccination rates in the world, and yet here especially, a second dose is essential for lifelong immunity. In the state of Victoria, recent research into measles cases has shown that a small number of people who have been vaccinated with just one jab can catch the catch and spread the super-contagious virus.
Before measles was eradicated in Australia, individual with just a single vaccination had a pretty good chance of coming into contact with another person who had measles. Similar to a second shot, this then gave them a natural boost in their antibody levels.
But what happens when immunity is left to wane? Australia was measles-free just five years ago, and since then, a new study has identified a possible emerging problem.
In Victoria, between 201
These are just your classic cases, either. Of the 13 secondary vaccine failures identified in this time period, each presented with a rash, though the individuals were less likely to have a fever, runny nose or cough. In one tragic instance, the infection was even passed on to two infants who were too young for vaccination.
"Overall, in countries that have eliminated measles transmission, this is likely to be a problem," lead author Katherine Gibney, an epidemiologist at the Doherty Institute and the Victorian Department of Health and Human Services.
" There isn't going to be an enormous number of cases, but it will be important in terms of recognition measles, because the cases are a bit different to those who aren't immune. "
The measles vaccine has been in use for the past 50 years, and it is easily the best and safest way to ensure immunity against this dangerous virus. In Australia, the efficacy of one dose is estimated at roughly 96.7 percent, while for two, it's more like 99.7 percent.
Today, most Australian children receive two doses, but before the 1990s, this wasn't routine practice. As such, there are many Australians aged between 20 and just over 50 who have only one dose, or perhaps, given Australia's lower vaccination rate in the 80s, none at all.
These individuals pose a unique threat to public health, even without interference from overseas. The authors found that 54 percent of these immunity cases were actually acquired in Australia, while only 23 percent were brought back from the Philippines.
"In most cases, people are unaware they need the second vaccine, or they just don't remember if they had one or two," says Gibney.
"Anyone who is unsure if they have had two doses In particular, adults born after 1965 may not have received two doses of measles vaccine during their childhood immunization routine. "
Very few people who get both doses will get the measles if exposed, but can still happen, as one case in this study exemplified.
"Our findings challenge the assumption of immunity among those who are fully vaccinated against measles and those with measles-specific [antibodies]," the authors write .
"The proportion of contacts who are fully vaccinated and / or [antibody-positive] and go on to develop measles is presumably low, but not zero." Far from being an argument against vaccination, it merely shows how important these health practices truly vein. According to the US Centers for Disease Control and Infection, situations like the one mentioned above happen very rarely; if they have, they will receive less and less contagious to others if they have received both doses.
The new study is obviously small in its scope, having only identified a total of 190 cases. It must be acknowledged that for four of the cases, secondary vaccine failure, documentation of the actual dosages were not available and thus the disease had grown, the
"Normally, if people have documented receiving two doses or measles vaccine we would be confident they won't contract measles, but that's getting greyer – this research has shown some vaccinated people are getting measles, "says Gibney.
The research was published in Clinical Infectious Diseases .