Neil Rau is an infectious-diseases specialist and medical microbiologist based in Oakville, Ont., and an assistant professor at the University of Toronto. Richard Schabas is a former public-health physician and was Ontario’s chief medical officer of health 1987-97.
Measles outbreaks in Europe – particularly a current one in Ukraine – with thousands of cases and dozens of deaths have focused attention on this disease. Despite the availability of a highly effective vaccine, measles survives into the 21st century courtesy, of a combination of disorganization, poverty and anti-vaccine ignorance. Measles remains an important disease of children in developing countries, with high infection rates and a real risk of serious complications and death, killing almost 90,000 children in 2016. But what does all this mean for Canada?
Measles is a highly infectious viral respiratory disease associated with a characteristic skin rash. Historically, virtually every child born in Canada got the measles, and many died. However, the 20th century brought two important changes. First, the mortality rate from measles dropped dramatically in developed countries. All children still got the disease, but with better health and nutrition, far fewer died. Then, starting in the 1970s, the measles vaccine almost eliminated the local spread of the disease. The current recommended regime – two doses in childhood – with high levels of population coverage has reduced the rate of measles in Canada to a tiny fraction of the pre-vaccine rate.
Put the triumph against measles in Canada into perspective. Without measles vaccine, we would expect about 350,000 cases in Canada each year. Instead, we see a few dozen reported cases. At current rates, Canada can expect to see a death from acute measles about once every hundred years or so. The borderline hysteria, fuelled by the media and public health, that greets a few cases is unwarranted.
Anti-vaccine sentiments are real but their numbers are small and not growing. In Ontario, for example, all exemptions (both medical and philosophical) under the school-immunization law have hovered around 2 per cent since legislation was introduced 35 years ago – a small and stable number. Our current levels of immunization are more than adequate to achieve herd immunity, which means that measles cannot spread in a sustained way. This protects everyone, even those who have not been immunized.
Anti-vaxxers are infuriating because they freeload on the population herd immunity. You can compare them to transit-fare evaders: The bus may run anyway, but if everyone took this attitude, public transit would collapse. Ditto measles immunization. However, the main harm anti-vaxxers cause is to their own children who are not protected from sporadic imported cases. Fortunately, the risk they pose to immunized children is negligible. While we regard anti-vaxxers with the contempt they deserve, severe enforcement policies directed at this group (e.g., withdrawing social benefits as proposed in Australia) would do more harm than good, as these tend to punish lower-income people.
Canada will see sporadic cases and small clusters of measles until the disease is eliminated worldwide. Anti-vaxxers are part of the problem but they are not the whole problem. Even with very high – more than 95 per cent – immunization rates, limited spread from imported measles persists in Canada because there will always be some people who are susceptible to infection. This is unavoidable because children under the age of one are not immunized; even two doses of measles vaccine are not foolproof ( 15 per cent of measles cases in the current EU outbreak are among those who have received at least one dose of measles vaccine); and we live in a free and open society that doesn’t force people to be immunized. Canadian measles outbreaks are nonetheless few, small and short because of our herd immunity.
Travel – not immigration – is what continues to bring measles to Canada. This is an important distinction in a world where scapegoating immigrants is increasingly commonplace. A traveller – be it a Canadian going abroad or a foreign visitor – is just as capable of bringing measles to Canada as a susceptible immigrant. There are far more travellers each year than there are arriving immigrants. Until global eradication of measles is achieved, episodic measles importation will remain a factor that we simply have to live with.
Canadians should be reassured that we are pulling our weight in measles eradication at a domestic level. We have not had sustained spread here for decades. We are not exporters of infection for other countries. But measles will remain a reality here for years, even decades, to come. Fortunately, our high immunization levels, our robust general health and our excellent health care mean that measles is no longer an important public health threat here. Stay calm, get your children immunized and carry on.