Vaccine-related adverse event rates found to be low in Ontario study

A new Ontario report on vaccine safety shows the rate of adverse events reported after vaccinations in the province is low.

The report says there were 56 serious vaccine-related adverse events reported in 2012, in a year when 7.8 million vaccinations were distributed in the province.

That is 7.2 serious events for every one million vaccinations.

Serious reactions were things like convulsions, seizures and anaphylaxis, an allergic reaction that can range from an itchy rash and hives to difficulty breathing and in severe cases shock.

The report says none of the serious reactions reported in 2012 was fatal.

The report is the first of what is expected to be an annual assessment of vaccine safety in the province published by Public Health Ontario.

The agency's director of immunization and vaccine preventable diseases, Dr. Shelley Deeks, says the goal is to be transparent about vaccines in a climate where there are many questions and misperceptions about the products.

The more success we have with immunization, the less the disease becomes as common or prevalent.- Dr. Shelley Deeks

"I feel we have a responsibility to provide this information back [to the public] … and probably do a little bit of a better job of communicating how safe our vaccines are," Deeks says.

"But also communicating that they're not perfect, and that no drug or biologic product is perfect."

The report covers vaccinations given at all ages.

And it makes clear that the adverse events reported may not have been caused by vaccines. A difficulty that arises in adverse event reporting is that something that happens after someone took a drug or got a vaccination may have been unrelated to the medical intervention — but there often is no way to tell. So the report says the events are "temporally associated" — linked in time — but may not have been caused by vaccinations.

There were 631 adverse events reported after vaccinations, but the bulk of them fell into the mild category. They included things like sore arms (252), rashes (137) and fever (47).

That leads to a rate of 4.7 adverse events for every 100,000 vaccines distributed in the province. That is well below the
national average of 9.4 per 100,000 vaccinations.

Deeks doesn't think that is because Ontario has far fewer events than other parts of the country, but rather that until recently there wasn't as much of an effort to get people to report these types of events as there is now.

The 2012 rate rose by 30.6 per cent from 3.5 and 3.7 per 100,000 vaccines in 2010 and 2011 respectively. Again, Deeks puts that down to increased emphasis on reporting, including the publication of new guidelines on surveillance for adverse events after vaccination.

She says the rates will likely continue to rise as the province's reporting falls into line with other jurisdictions.

It is generally believed that adverse event numbers related to drugs and vaccines are under-estimates, because some people won't bother seeing a doctor or filing a report.

'Victim of our own success'

Deeks acknowledges that is likely true here as well. But she believes the under-reporting is likely mostly in the mild category.

That's because doctors are required to file reports if they see patients who may have suffered an adverse reaction to a vaccination. 

While Deeks believes it is important to share information — the good and the bad — about vaccines with the public, she knows there could be a downside.

 Where 56 out of 7.8 million is a small number, she's aware some people will focus on the 56, inflating its significance.

She says public health needs to do a better job putting numbers like these in context, contrasting them with the adverse events that are averted because vaccination prevents so many infectious diseases.

The World Health Organization estimates that vaccines prevent two million to three million deaths a year globally, which is in the range of 200 to 300 an hour.

"I think we've been the victim of our own success," she says. "The more success we have with immunization, the less the disease becomes as common or prevalent. So people forget about the diseases and then are more concerned about the safety … of the vaccine."

Reminding people of that context may become even more difficult going forward because increasingly children are born to parents who themselves never experienced measles, mumps, and chickenpox, and who haven't even the faintest memories of when polio outbreaks petrified parents.

The report says just over half of adverse events were reported in children and teens 18 and younger. The percentage share of the reported adverse events decreased with each increase in age demographic.

Interestingly, females reported far more adverse events then men; women and girls made up 67.4 per cent of the reports. And in women older than 18, the predominance was marked, with 82.6 per cent of the reported events in women.

Why the substantial difference? Deeks says it may be related to differences in the way women and men use health care. For instance, women may be more likely to keep up on their vaccinations than men — people who don't get vaccinated don't have vaccine-related reactions. As well, women may be more likely to report a reaction to
a vaccination than men, Deeks says.

The vaccine for which there were the greatest number of adverse events reported was influenza. But Deeks says that can be explained by the sheer volume of the province's flu shot program.