By: Yashoda Valliere


During the winter, we spend much more time in close contact with each other – crammed into HSR buses, cafés, or libraries – and to add to our woes, our immune systems are compromised by the stress of exams. As a result, a university at this time of the year can be a veritable breeding ground for the flu.

The flu shot is free in Ontario and is a vaccine for this year’s flu viruses. A vaccine contains inactive (“dead”) viruses, which are injected into your body so your immune system can learn to recognize their unique “ID tags” and form antibodies specifically targeted to them. Due to the high mutation rate of the flu virus, new strains emerge each year, and the flu shot changes accordingly.

Every February, the World Health Organization releases what they deem to be the three most common and dangerous strains for the year, and the new vaccines are made specifically for those three. Since there are only three strains of flu virus in your vaccine, it does not protect against every strain of the virus and there is still a chance that you could get the flu.

So why should you consider getting the flu shot? After all, you might be thinking, “I’ve never gotten it and yet I’ve rarely had the flu, so obviously the vaccine is unnecessary.” To understand how vaccination programs really work, you need to look at the bigger picture, beyond yourself. Vaccines protect a large population through a principle called “herd immunity.”

For example, imagine you have five people in a row, and none of them have immune protection against the flu. If one person gets the flu, like a row of dominoes, a “chain of infection” is born. However, if one of them has been vaccinated, the chain of infection is broken by that person.

Herd immunity operates on this principle at a larger scale. If enough people in the population are vaccinated, then the chains of infection are broken at a relatively early stage, preventing massive epidemics. If a high proportion of the population is vaccinated, then even those who are unvaccinated are indirectly protected – you can mentally picture them as being isolated in a “bubble” of vaccinated people around them. If you’ve never been vaccinated against the flu and yet you haven’t gotten sick, you were in one of these protected bubbles, thanks to the vaccinated community around you.

In order for this indirect protection to be conferred upon vulnerable members, a certain proportion of the population must be vaccinated – this is called the “herd immunity threshold.” If the proportion of vaccinated people falls below the threshold, the “bubbles” might come in contact with each other – an infectious person could meet a susceptible person, and thus a new chain of infection would form. The herd immunity threshold for influenza is estimated to be greater than 60 per cent. If we all continue thinking that we don’t need to get the shot, we won’t meet the threshold, and the vulnerable members of our community, such as infants and the elderly, will not be protected.

This being said, the flu shot isn’t perfect. It’s known to have side effects such as aches, fever, chills, cough and nausea. This happens because your immune system thinks that you have the flu, and it’s fighting against it. It’s understandable that you don’t really want to be dealing with all the side effects on top of November crunch season. Or, you could be preventing a more serious bout of the actual flu from hitting you later in the winter. The cost-benefit analysis is up to you.

Another reason you might not want to get vaccinated are the horror stories of severe reactions. If you have an egg allergy you should avoid the shot, as the vaccine viruses are grown in chicken eggs. Rare adverse reactions do exist, but it’s important to remember that the media, in pursuit of sensationalist headlines, tends to give these cases a disproportional amount of coverage. Research has shown that the risk-benefit ratio for the general population is overwhelmingly in favour of vaccination.

At the end of the day, vaccination and anything else that affects your body is 100 per cent your personal choice. No matter what you decide, it’s good to have the facts to make an informed decision.

One last note: After the vaccination, your immune system takes about two weeks to build up enough antibodies to be effective – so if you decide to go for it, the sooner the better!

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