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(Carolyn Kaster)
(Carolyn Kaster)

The H1N1 question

Is the flu virus mutating dangerously? Add to ...

Thursday, Nov. 19

Q: If enough people get the flu and get vaccinated then there won't be anyone who can spread the flu, right? So I can avoid getting vaccinated and still be safe. Do you follow what I'm saying?

A: The scientific term for the idea you are describing is herd immunity. When a majority of people (or animals) in a group are immune to a disease, the disease cannot find a viable host to take hold so it can't spread. Therefore, even if you have not been infected or vaccinated, you effectively get immunity without paying the price (the price being a needle or an illness). The problem is that for herd immunity to kick in, anywhere between 50 and 90 per cent of the population needs to immune and practice good hygiene. (No doubt you have heard the admonitions to hand washing and sleeve-coughing.) With influenza herd immunity kicks in when about 80 per cent of the population is immunized. But even that goal is ephemeral because influenza viruses mutate easily and often, so herd immunity is virtually impossible to attain. Currently in Canada, about 20 per cent of the population has been vaccinated against H1N1 and about 10 per cent has been immunized naturally through illness. That is far short of the 80 per cent threshold that would allow you to be a freeloading member of the heard so your idea, while clever, won't be too effective.

Wednesday, Nov. 18

Q: We've been hearing about the flu pandemic and the importance of vaccination for weeks. But none of the stories seem to say how many people have actually been vaccinated, how many had the flu and how many died. What's the deal?

A: According to the Public Health Agency of Canada, approximately 20 per cent of the population has been vaccinated against H1N1 influenza so far. That is about 6.6 million people - or the number of doses of vaccine distributed as of Nov. 07. (It takes about a week for all the vaccine to be used after delivery.)

By the end of this week the number of vaccine doses delivered will have surpassed 10 million.

An estimated 10 per cent of the population has contracted H1N1 flu so far, according to PHAC. Not all 3.3 million or so of them have been tested. The estimate is based on sentinel testing (or sampling, if you prefer) around the country. Infectious disease experts estimate that, before all is said and done, as many as 10 million Canadians will get sick with H1N1 flu, roughly the same as a 'normal' flu season.

As of Nov. 07, a total of 3,764 people have been hospitalized with severe H1N1 influenza, including 606 people admitted to intensive care. Hospitalizations are most common in the under-20 age group, which is unusual for influenza. Those admitted to ICU are principally in the under 5 and 45-64 age group, which is also unusual for influenza. While relatively few seniors are contracting H1N1 (they have some natural immunity from exposure to similar strains of the virus), they have the highest death rate when they do fall ill.

To date, there have been 198 deaths, the bulk of them in Ontario and Quebec. Here is a breakdown:


Deaths (as of Nov. 17/09)

British Columbia












New Brunswick


Nova Scotia


Prince Edward Island


Newfoundland and Labrador




Northwest Territories






Tuesday, Nov. 17

Q: I read that there's worldwide shortage of Tamiflu. But I also read that Canada has a huge stockpile. Can you tell me who's getting this drug and why?

A: As part of the pandemic preparedness plan, Canada purchased 55 million doses of the antiviral drugs oseltamivir (Tamiflu), and zanamivir (Relenza). The medications have been distributed to provinces and territories on a per-capita basis, and the medication can be prescribed by physicians.

Antivirals are used to slow the replication of the H1N1 virus to lessen symptoms and reduce the spread of illness to others. But they have to be used early - within 48 hours of onset of symptoms - to be effective.

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