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CTV.ca, with the help of infectious disease expert Dr. Neil Rau, answers your questions about the coming swine flu vaccine.

Should I get the vaccine?

For some of the priority groups identified by The Public Health Agency of Canada, the vaccine is urgently and strongly recommended. Others will need to make an individual decision based on their assessment of available information. The vaccine will not be mandatory.

The priority groups for vaccination are not those at highest risk of contracting swine flu, but those at highest risk of developing complications and dying. PHAC has identified these groups as a priority:

• pregnant women (see below for further details);
• children six months to under five years of age;
• people with chronic medical conditions under the age of 65;
• people living in remote and isolated settings or communities;
• health care workers involved in pandemic response or who deliver essential health services;
• household contacts and caregivers of individuals who are at high risk and who cannot be immunized (such as infants under six months of age or people with weakened immune systems)

Vaccine supplies have been limited in these first couple of weeks, so patients are being prioritized further, province-by-province. PHAC has promised there will be enough vaccine for all Canadians who need or want the vaccine by December, though it's unclear how active H1N1 will be by then.

There are still questions about whether everyone will want to be vaccinated. Keep in mind that H1N1 causes only mild flu in most people; in fact, some Canadians may have already been "immunized" through an H1N1 infection (see below for more). Otherwise healthy may choose to wait until vaccine manufacturers gather more safety and effectiveness data.

The vaccine is also not appropriate for infants under six months of age or anyone who currently has a fever. Those with compromised immune systems should check with their doctor about whether the vaccine is appropriate for them.

If I've already had swine flu, will I need the vaccine?

If you're certain you've had H1N1, you won't need the vaccine, at least for this coming season. (The virus may change in future seasons, requiring the need for a new vaccine.) The problem is that only those who underwent lab testing can know for certain they had swine flu. But since strain testing is no longer being routinely done, most people will not know if they have had H1N1 until an accurate blood test becomes available.

Even if you have been infected with swine flu already, it's likely safe to get the swine flu vaccine. Remember that seasonal flu vaccines are administered to the general population without the use of a blood test beforehand.

Where can I get the vaccine?

Here's , province by province. Call your doctor or pediatrician to find out if they are administering the vaccine as well.

How many doses do my children need?

Children over the age of 10 need only one dose of adjuvanted vaccine, PHAC now advises. And children over six months but under three years are encouraged to receive two half-doses, given at least 21 days apart.

Most children between three years and nine years old need only one half-dose of vaccine, Canadian health officials have decided. But children in that age group who have chronic health conditions should also still receive two half-doses.

There's a chance this may not be the final word. PHAC notes that further adjustments to the dosage recommendations may still be made, once the results of additional research and clinical trials on vaccine effectiveness are available.

Parents should strive to get their child at least one vaccination, because even one should provide a measure of protection.

How effective is the new vaccine?

Trials conducted on the GSK vaccine in Europe have found the vaccine produces antibodies in 85 to 98 per cent of adults aged 18 to 64 -- an excellent, though not perfect, effectiveness rate. But then, even seasonal flu vaccination doesn't provide 100 per cent immunity. In years when the strains of the flu virus in the seasonal vaccine have been a good match for the dominant strains circulating in the community, seasonal flu vaccine has been shown to reduce infection by 70 to 90 per cent in healthy adults.

The vaccine may be somewhat less effective in children under 10 years of age. However, promising recent information from GSK indicates that one half-dose of adjuvanted vaccine provided adequate immunity to children over six months of age.

As things stand now, kids under the age of 10 are still being told to get two half-dose shots given 21 days apart. However, this recommendation may be revised in the future, based on the promising information just cited.

It should be noted that it takes about 10 days after vaccination for antibodies to develop in the body and provide protection, so a recipient is still at risk for infection in the two weeks after a shot. The vaccine also may not work as well in people who have problems with their immune systems or who are taking medication that affects their immune systems; however it is still important for these people to consider vaccination.

How long will the H1N1 vaccine provide protection?

Influenza viruses are notoriously adaptable and strains change constantly. While we haven't seen any evidence yet that H1N1 virus has mutated, it is likely to do so by next year. It almost certainly will also still be a dominant flu strain. So by next fall, we will likely need a new vaccine to protect us against any drifted form of H1N1. By then, though, the seasonal flu vaccine will almost certainly incorporate protection against H1N1 swine flu.

By that point, we will also have a much clearer idea of the seriousness of H1N1, the safety of the vaccine, and the need for ongoing annual, large-scale vaccination. 

How safe is the new vaccine?

The companies making H1N1 flu vaccine have been making seasonal flu vaccines for years and have good track records of safety. Safety trials looked for immediate side effects from the vaccine, such as allergic reactions and something called "oculorespiratory syndrome," which would likely show up within a few days of administration and in relatively small numbers.

Rarer side effects (see below), if associated with the vaccine, will not appear until many (i.e. millions) have received the vaccine. For this reason, Health Canada has said it will work with other world health agencies to monitor the safety and effectiveness of the vaccine in post-marketing surveillance, and "to ensure the timely communication of any potential adverse events following immunization."

At this point, at least 200,000 people have received a Canadian form of the vaccine worldwide.

Are there side effects?

Clinical trials have found the most common reactions after getting the adjuvanted vaccine included pain, swelling and redness at the injection site. These reactions occurred to less than 10 per cent of patients vaccinated. Such reactions are to be expected because the adjuvant helps the body develop a stronger immune response by increasing the inflammatory response.

Other reported reactions were fatigue, muscle and joint pain, and headache. In younger children, a fever, drowsiness, irritability and loss of appetite were also reported in low levels.

Can I get the  vaccine if I'm allergic to eggs, thimerosal or formaldehyde?

People with egg or chicken protein allergies are generally told not to take flu shots because the vaccine is produced in eggs. But Canada's chief public health officer, Dr. David Butler-Jones, says the egg residue left in the vaccine after purification is small and that people with egg allergies who want to get the vaccine can do so if it is in a setting where they'll be cared for by a doctor if they develop an allergic reaction.

Trace amounts of thimerosal or formaldehyde are also used in vaccine production too. Those who have had allergic reactions to other vaccines should not get the flu vaccine without talking to their doctor or allergist.

Why did it take so long for the vaccine for become available?

Flu vaccine production is inherently slow; the total production and testing time is about 19 weeks. That's in part because the production begins with growing viruses in fertilized chicken eggs. For every shot, at least one egg has to be infected with the virus, where it then replicates before being extracted and purified into a vaccine. Even after the antigen was produced, the resulting vaccine then had to be tested for several weeks in clinical trials on different kinds of patient groups (adults first, then kids, etc.) Then, the vaccine had to go through regulatory approval. Finally, it had to be packaged and shipped, distributed to the provinces and then distributed to flu shot clinics and doctors' offices.

What is an adjuvant and why is Canada using one?

An adjuvant is a chemical additive used in some vaccines to ramp up the response the immune system generates to a vaccine. Adjuvants aren't new in Canada; they're already used in pneumococcal and meningococcal vaccines, for example.

With an adjuvant, less pure vaccine antigens are needed, so one dose of vaccine can be stretched into four doses. An adjuvant boosts immune response so that recipients are more likely to develop antibodies against the virus. It also makes the immune response more "durable," so it lasts longer, and it creates a wider response, so that if H1N1 "drifts" or changes, this vaccine should still offer some protection.

GSK says its vaccine contains its own proprietary adjuvant system, called AS03. It is a based on squalene, an organic compound obtained from fish oil and mixed with water and vitamin E that is safe, despite Internet-based rumours to the contrary.

While the U.S. is not using an adjuvant in its swine flu vaccines, Canada chose to use an adjuvant after there were initial problems with slow vaccine production and the WHO requested manufacturers use "antigen sparing strategies" to stretch out supplies.

Because flu vaccines don't normally use an adjuvant, GlaxoSmithKline could not use the" fast-track" vaccine approval system that allows seasonal flu vaccines to be tweaked every year with small adjustments to the strains. Adding the adjuvant made the Canadian version of the pandemic vaccine different enough from seasonal flu vaccine in its design that a new licence was required and more clinical trials were needed to assess safety.

What is squalene?

The adjuvant used in the swine flu vaccine is made with vitamin E, water and squalene, derived from shark liver. Squalene is an organic substance found in all humans; our bodies use it to synthesize sterols - such as cholesterol -- and steroids. It is also found in all animals, plants, and a variety of foods, cosmetics, and medicines.

Some websites have linked squalene to the anthrax vaccines to Gulf War Syndrome, but those allegations have been shown to be false. Squalene was never used in the vaccines. And while anti-squalene antibodies were found in some of those with Gulf War Syndrome, they are also found in the blood of people who have never received a vaccine containing squalene.

Over 22 million doses of squalene-containing vaccines have been administered around the world, mostly in adults. "The absence of significant vaccine-related adverse events following this number of doses suggests that squalene in vaccines has no significant risk," says the World Health Organization.

Can those with seafood allergies get the vaccine?

Since the squalene component of the vaccine adjuvant is made from shark liver oil, many have wondered whether those with fish or shellfish allergies can receive the vaccine. The adjuvant is distilled several times to purify it, a process that destroys any fish proteins that could cause allergic responses. So those with shellfish or seafood allergies can still safely get the vaccine.

I'm pregnant; should I get vaccinated?

While pregnant women are not at higher risk of contracting swine flu, they are at higher risk for severe disease if they become infected in their second and third trimester. For that reason, they should consider getting the vaccine, especially if they have underlying disease. An added bonus is that mothers who are immunized while pregnant may help to protect their infant after birth.

Because there hasn't been much data on the use of adjuvanted flu vaccines in pregnant women, these women had been told to wait for the unadjuvanted vaccine. But in late October, experts advising the World Health Organization reversed their recommendation and said that based on data review, they now recommend that any H1N1 vaccine be given to pregnant women.

Because pregnant women were once recommended to get the unadjuvanted vaccine, this led to the false perception that the adjuvant is not safe. This perception is untrue; all study data so far indicates adjuvanted vaccine is as safe as unadjuvanted vaccine in pregnancy.

I'm currently breastfeeding; what do I need to know?

If a breastfeeding woman develops flu symptoms, she should speak to a health care provider as quickly as possible. Women who become ill can safely continue to breastfeed their babies. While it isn't known if the flu virus can be passed through breast milk, the benefits of the antibodies in breast milk means that it continues to be the best way to keep your baby healthy.

The Public Health Agency of Canada recommends both the seasonal flu vaccine and the H1N1 flu vaccine for breastfeeding women. Women who are breastfeeding should receive the adjuvanted H1N1 flu vaccine, as it offers the best way to protect their health and the health of their infant.

Women can safely take antiviral medications while breastfeeding. Only low amounts of antiviral medication are passed through breast milk and breast milk continues to be a baby's first line of defence against all illnesses.

Can I opt to get the vaccine without adjuvant?

Canada has ordered 2 million doses of unadjuvanted H1N1 flu vaccine, but the current word is that only pregnant women can access the unadjuvanted vaccine. At one point, federal officials said unadjuvanted vaccine would be available for toddlers aged six months to 3 years, noting there had not been much research on the safety of adjuvanted vaccine in children this young. But PHAC now recommends adjuvanted vaccine for this age group.

There is no evidence to suggest that the adjuvanted vaccine is unsafe, but there are studies that suggest the unadjuvanted H1N1 flu vaccine does not deliver as strong of an immune response. Even the best unadjuvanted flu vaccines protect only six out of 10 people who get the shot, studies have suggests. This may be modified, however, based on encouraging information from the manufacturer. The PHAC, meanwhile, says the adjuvanted flu vaccine could boost protection rates to as high as nine in 10.

I don't like needles. Can I get that vaccine that's sprayed up the nose?

No, FluMist is not available in Canada. The company that makes it, MedImmune, only recently applied for a licence to sell their seasonal flu vaccine in Canada. That application is still in the licensure process, so they cannot sell any flu vaccine in this country yet. Canada is buying H1N1 vaccine from only one supplier, GlaxoSmithKline, whose vaccine is injectable.

Is there mercury in the swine flu vaccine?

The flu vaccine contains a small amount of thimerosal. That's because the vaccine is delivered in multi-dose vials, so needles are inserted into the vial more than once to extract doses. For that reason, all flu vaccine bottles (seasonal and swine flu) contain small amounts of thimerosal as a preservative.

Thimerosal is a mercury-based preservative, but it's made of ethylmercury, not methylmercury, the kind that can accumulate in the body and has been linked to neurological damage. Studies have shown that ethylmercury from vaccines disappears rapidly from the blood. The levels of ethylmercury in vaccines are minute and have not been shown to cause harm, says the Public Health Agency of Canada.

It's estimated that there is four times as much mercury in a can of tuna fish than in the thimerosal in the H1N1 flu vaccine.

What about the 1976 flu vaccine?

Many remember the Fort Dix outbreak flu in 1976, in which a number of Fort Dix recruits came down with a new strain of flu that turned out to be also partially swine-derived. A hastily-prepared mass vaccination program was undertaken in the ensuing panic. Millions of Americans and some Canadians got a shot for a virus that turned out not to be a good spreader and that quickly fizzled out. Among the millions who were immunized, about 500 came down with Guillain-Barré syndrome, a paralyzing neuromuscular disorder that is generally temporary, and about 25 deaths were linked to the vaccine.

Although the vaccine had appeared safe in initial testing, the handful of rare neurological side effects became evident only after millions of doses had been given. What went wrong in that vaccine is still not clearly understood to this day.

Manufacturing processes are much improved in terms of purity today than they were in 1976. On the other hand, the 1976 swine flu vaccine did not use an adjuvant, raising concerns about whether the "swine" flu-derived vaccine are associated with higher risk of Guillain-Barre syndrome. For this reason, Health Canada has requested the manufacturer agree to "post-market commitments" surveillance.

Nevertheless, many argue that more lives were saved from flu prevented by the 1976 vaccine than were killed by the rare neurological side effects. And it should be noted that the kind of side-effects seen with the Fort Dix vaccine has not been seen with any subsequent seasonal flu vaccines used thereafter.

The WHO acknowledges that "special safety issues will inevitably arise during a pandemic when vaccine is administered on a massive scale." Some adverse events will be coincidental - that is, associated in time with vaccine administration, yet not directly caused by the vaccine. There could also be events directly caused by the vaccine, it said, but "given the safety record of seasonal vaccines, such events are expected to be rare."

If I've had Guillain-Barre Syndrome in the past, can I get the vaccine?

Because it is difficult to determine what brings on GBS -- most cases are idiopathic, meaning no one knows what caused it -- anyone who has ever developed Guillain-Barre Syndrome should speak to their doctor about whether they should get this year's flu vaccines.

Will I still need the seasonal flu vaccine?

The answer is still not clear. At the current time, H1N1is "crowding out" all other flu viruses and appears to be the dominant strain in the Northern Hemisphere. That means Canadians who get flu illness right now are most likely becoming ill with swine flu.

We know that the seasonal flu vaccine is ineffective against H1N1. But it still has potential benefit for seniors over 65 who are most at risk of seasonal flu, but at minimal risk of swine flu. Therefore, most provinces are offering seasonal flu vaccine to people 65 and older and residents of long-term care facilities first, while the rest of the population is being advised to get the swine flu vaccine first.

However, as the season progresses, we might see a change in which swine flu no longer crowds out seasonal flu. In that case, seasonal flu may become a bigger player again and younger Canadians may be advised to get seasonal flu vaccine later in the season. However, this recommendation may change depending on which seasonal flu strain begins to circulate.

Can the seasonal vaccine and the novel H1N1 vaccine be given at the same time?

Both vaccines can be given together if given at separate injection sites (separate arms), the Public Health Agency of Canada has said. However, the immediate need for most people is to get swine flu vaccine, since H1N1 is crowding out seasonal flu strains. And with long waits to get the H1N1 vaccine, the possibility of getting both flu vaccines at the same time is not even an option to most Canadians.

The National Advisory Committee on Immunization is urging provinces and territories to move ahead with seasonal flu shots for all Canadians, regardless of age, as soon as is feasible.

The one caveat to getting both vaccines at the same time is that it would be difficult to appraise potential adverse effects of either vaccine, if they are given simultaneously.

Do you have questions about the coming swine flu vaccine? Send them in and we will keep this page updated with the answers and all the latest information. Send your vaccine questions to health@ctv.ca