The Americans stated their position firmly on whom to vaccinate with the new pandemic vaccine, while Canada took an “undecided” path. To quote former Prime Minister Jean Chretien -- who spoke in a totally different context (regarding the presence of weapons of mass destruction in Iraq to justify invasion) -- “A proof is a proof. And when you have a good proof, it's because it's proven.”

On the balance of risks, we still need more information to decide who should get the new vaccine. If we already had a vaccine that had been tried and tested on millions, the path forward would be clearer right now. But we don’t, so pending that information, the Canadian approach is the prudent one.

Think back to 1976, to the infamous Fort Dix flu outbreak, when a different swine flu-derived vaccine was rapidly approved and implemented. That vaccine program unfortunately caused rare neurological side effects and deaths that became evident only after millions of doses had been given.

To put this in perspective, some argue that more lives were saved from flu prevented by the 1976 vaccine than were killed by this side effect. And this side-effect profile has not been seen with subsequent seasonal flu vaccines in use after that time (though none were derived from “swine flu”). Nevertheless, we are now contemplating implementing another swine-flu derived vaccine before all of the safety data comes in.  Therefore, it makes sense to move ahead with vaccination for those who face a substantially greater risk from swine flu as compared with seasonal flu. As the vaccine safety and effectiveness data rolls in, we can scroll down the list to those at lesser risk. But even at this moment, are there groups who are conclusively at greater risk? This too remains unclear.

Pregnant Women

An article released this week in The Lancet showed that pregnant women are at higher risk of complications (including death) from swine flu than non-pregnant women. The unknown is whether this is a different picture from what we see with seasonal flu? Maybe not.

We know that seasonal flu is four times more likely to kill pregnant women than non-pregnant women. Yet we never drew urgent attention to the fact that only 1 in 7 pregnant women are vaccinated against seasonal flu until now. This is despite the fact that they have been considered a high-risk group worthy of vaccination for the last few years in Canada and the U.S.

Perhaps we did not notice this gap in practice because the absolute numbers of deaths in this group were rare. With the current focus on swine flu, the medical community and media are scrutinizing every case. Even with the recent Lancet report, the swine flu death rate in pregnant women is estimated to be only 1 in 300,000 cases. Obviously, many pregnant women would need to be infected with swine flu before the impact would have become noticeable.

This being said, pregnant women in their second or third trimester should see their doctor to consider antivirus treatment as soon as they suspect they have the flu. So how urgent is the need to vaccinate pregnant women in their third trimester? I can’t say yet.

(Even if Canada ultimately moves the American way to recommend the new vaccine for pregnant women, I suspect that many expectant mothers will not opt for it, especially as we assess the safety profile of the new vaccine.)

What about the other groups mentioned by the CDC?

• People who live in homes with children under the age of six
• Health workers and emergency personnel
• People from six months to 24 years old
• Non-elderly people with underlying health problems

Children under two years of age and the elderly with health problems have historically been at higher risk of death from seasonal flu than the general population. But how much more serious is swine flu than seasonal flu for these groups? In fact, some are at a lower risk: the elderly are likely to be immune based on the data to date.

Health care workers and emergency workers are initially at higher risk for disease during the early phases of a pandemic; however, we are well past that initial phase in the northern hemisphere. As an otherwise healthy health care worker, I am not certain that I am at any higher risk than anyone else.

And as for the otherwise healthy people within the above groups, we still don’t have a clear picture of the additional risk of swine flu as compared with seasonal flu. Therefore, waiting for more information from the ongoing swine flu experience in Australia and other southern hemisphere countries is wise. If some of these groups prove to have a significantly greater risk with swine flu than with seasonal flu, they probably should get the vaccine sooner rather than later. For others whose risk proves no different from getting seasonal flu, waiting for more safety data on the vaccine is a reasonable approach.

I am optimistic that the vaccine will prove to be safe and effective. Within a few months, if we get confirmation of the safety of the vaccine, balanced against a deeper understanding of the risk posed by swine flu, I too may roll up my sleeve.

And, let's not confuse the new pandemic vaccine with seasonal flu vaccine. As always, I'll still be getting that shot.

MORE: CTV.ca answers some frequently asked questions about the coming swine flu vaccine