������Ƶ

As the school year gears up, writer Jenny Hall spoke with Dr. Shelley Deeks about vaccines: do they work, are they safe, and why do some people fear them?

An M.D., Deeks is a professor in the Dalla Lana School of Public Health and the Medical Director for Immunization and Vaccine Preventable Diseases at Public Health Ontario, where she provides medical leadership for the program area of immunization and vaccine-preventable diseases (IVPD), as well as medical and scientific advice on vaccines and immunization programs and vaccine program evaluation.

What are the rates of childhood vaccination? Are they going down?

We don’t have an immunization registry in Ontario, so we don’t know what our vaccine coverage or uptake is for infants or children before school age. We do have the immunization records information system, which is a school-based system, so we know coverage for vaccines at school age. Coverage has been relatively stable over the past 5 years. However, there’s been a slight increase in people who have registered conscientious objection to immunization.

In general, coverage is high for vaccines that require few doses and are administered only in the first few years of life (i.e., rubella), however there is a need to improve coverage for other vaccines, especially those which require multiple booster doses throughout life (e.g., pertussis or whooping cough).

Reading the news there seems to be an anecdotal sense that fewer people are having their kids vaccinated.

You’re right. There’s been increasing reports of vaccine hesitancy over the past fifteen years or so. However, it’s important to note that the people who are hesitant to receive vaccinations are really diverse. A small proportion of the population refuses all vaccines. Then you have people who will accept every single vaccine. Then you’ve got a group who are hesitant. They may receive some vaccines but not others, or they may delay vaccines.

What has been the impact of childhood vaccines?

There is a huge body of evidence that they work. They’re so effective that most of the diseases they prevent are now rare. These diseases have serious complication and fatality rates. The only disease that’s been eradicated in the world is smallpox, and that was due to immunization. Right now, there are only three countries in the world left where there is endemic polio. So hopefully that will be the second vaccine-preventable disease that will be eradicated in our lifetime.

And then there are diseases that have been eliminated in a group of countries. In Canada, measles and rubella have been eliminated. We do get cases because they’re not eliminated elsewhere in the world—we have importations of measles, for example, and we do have chains of transmission that happen because of these importations. These cases tend to occur in people who are not immunized. But for the most part, we just don’t see these diseases anymore, and they’re considered eliminated in Canada.

Is part of vaccine hesitancy that we don’t have collective experience of how awful these diseases are anymore?

I think that’s part of it. I currently sit on a World Health Organization committee, and in a number of countries, they’re clamouring for vaccines, but they can’t afford them. Hesitancy would not be such an issue in these countries.

Are vaccines safe?

People are concerned about whether vaccines are safe, and rightly so. Vaccines are different than drugs. They’re given to the general population, so there are different standards for vaccines. Having said that, the clinical trials that have to occur before vaccines are licensed are quite strict and rigorous. Vaccines are among the safest tools of modern medicine, and serious side effects are rare. Yet people still question the safety of vaccinations. We saw that recently when the HPV vaccine was first released. Once vaccines are licensed we continue to monitor vaccine safety.

In 1989 The Lancet published a paper that suggested the measles-mumps-rubella vaccine caused autism. It was later deemed fraudulent and retracted. How much of an impact did that paper have on vaccine hesitancy?

It’s had a huge effect. The author was stripped of his license in the UK, but he had a dramatic effect on vaccination coverage there. Then he went to the US and there’s been a movement of celebrities there, most notably Jenny McCarthy, who have presented themselves as immunization  experts and presented their stories of vaccines being associated with autism. Yet the alternate viewpoint wasn’t really heard, though more and more celebrities are now speaking out in favour of vaccines. We need to do better job, in the medical community, of telling compelling stories. We need to explain how safe vaccines are but also be very open about the risks.

What are the risks?

It depends on the vaccine. Each has its own list of side effects, but serious side effects are very rare. Something like anaphylaxis—an immediate allergic reaction—occurs in about 1 in a million, while local reactions, like pain or swelling at the injection site, are more common. But we do need to be clear that there’s no perfect vaccine, just like there’s no perfect drug.

Can you explain the concept of herd immunity?

The basic definition of herd immunity is the proportion of subjects with immunity in a given population. You’re probably asking about what’s called the “herd effect.” This is when you get protection in the population that isn’t immunized via the population that is. Human papillomavirus—HPV—is a good example. In Ontario, we immunize girls. It’s a very effective vaccine that protects against two types of HPV that cause about 90 per cent of genital warts, and two types of HPV that cause about 70 per cent of cervical cancers. The first cohort of girls that were immunized are now in second year university.

It will take us a number of years to look at the impact on cancer, because of the interval between having HPV and developing cervical cancer. But we can look now at whether the vaccine had an impact on warts. Australia had the first and  largest HPV vaccination program in the world. They immunized all their girls from age 12 to 26. They did a study looking at the incidence of genital warts in young adult women and young adult men. Not only had the incidence decreased significantly in women, but it decreased in men. That’s the herd effect: the men, who weren’t vaccinated, benefited from the program.

I often hear people say that that they don’t need to have their children vaccinated. The thinking is that if everyone else is vaccinated, their child gets protection without needing to be vaccinated. The herd effect does not apply to every disease. With tetanus, for instance, the only way you can protect yourself is by being vaccinated.

Some people object to vaccines because they don’t like the government telling them what to do.

Yes, people think that immunizations are mandatory for children in Ontario. But we actually don’t have mandatory immunization legislation here. We have a mandatory choice. Parents have to make a choice. They can philosophically object—they have to fill out forms and swear an oath—but they aren’t allowed to not make a choice.

Jenny Hall is a writer with the office of the vice-president (Research & Innovation)