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Column originally published Oct 6, 2009

Swine Flu Vaccine Is Safe

Question: We have a healthy five-month-old son. Our two older daughters have asthma. As a result, we have been getting flu shots every year. In the last few weeks, I have heard a lot about this swine flu and the vaccine that is coming out. I am nervous and confused whether we should get it or not. Some of our friends said that the vaccine is so new and that it may not be safe. We would appreciate your advice.


You are not the only one that is confused. The amount of news generated by the media can be scary. Let me try to clarify this a little for you and for other readers.

There are three types of influenza viruses: A, B, and C. Influenza C infection is very uncommon and most people have never heard of it. Most of the time, when we talk about influenza, it is influenza A or B. Influenza infection is mainly spread from person to person, through droplets of respiratory secretion from sneezing or coughing. Once infected, a person develops antibodies to the specific strain of influenza virus.

Influenza viruses are very smart. In order to make sure that they have as many victims as possible, they swap their genes with each other and keep changing their genetic makeup to counteract our immune system. When there is only a small change in their genes, we still have partial immunity if we have been infected or immunized with a similar virus before, and we wonʼt get too sick. If there is a big change in their genetic makeup, most of the population would have no immunity to it, and a large outbreak will occur.

This is exactly the case with H1N1, or swine flu, that we are concerned about now. Researchers have discovered that this particular strain has genetic material from many different strains of influenza virus. Because its genetic makeup is so different from other influenza viruses in the last few decades, most of us have little or no experience with this particular H1N1 strain. As a result, we have a major pandemic affecting all corners of the world.

As you know, this H1N1 virus was first recognized in Mexico in April 2009, barely six months ago. It rapidly spread to United States and Canada in May and June, at a time when our normal influenza season should have slowed down. Instead, we saw outbreaks of influenza across the country, almost exclusively due to H1N1 virus. Fortunately, the Canadian summer stopped the spread of this virus, although it is making a comeback because of cooler weather.

The majority of those infected have had mild to moderate illnesses. Some still require admission to hospital, and a smaller number had died. With seasonal influenza, the most susceptible ones with the highest mortality are seniors over 65 years of age. Not so with H1N1: fewer than expected seniors got sick, and very few of them died. It is speculated that they most likely were infected with similar strains of influenza decades ago, and their immune system still has memory of the virus and able to fight it off.

We are very lucky that we have an excellent health care system in Canada. You may recall that a few years ago, there was great concern about another influenza virus: the avian flu. As a result, federal and provincial governments as well as health care facilities have been making plans to deal with influenza pandemics. This planning is being executed now to fight the H1N1 pandemic: medications and supplies are stocked up, a new vaccine is on the way, as well as public education to reduce the spread of this virus.

Influenza vaccines, commonly known as flu shots, have been widely used for several decades to prevent outbreaks of influenza every winter. The technology that is used in the production of influenza vaccine has greatly improved in recent years. Only a very specific fragment of the virus that can induce protective immunity is being used to produce the vaccine. As a result, influenza vaccines produced in recent years are more effective and safer than before.

Shortly after H1N1 was discovered, the process of manufacturing influenza vaccine against this strain of influenza virus got underway. Australia was the first country to test this vaccine, followed shortly by China. So far this vaccine has been shown to be safe and effective. Although it is a new vaccine, the manufacturing process is similar to what has been used in recent years. There is no reason to believe that this vaccine is unsafe.

What is different is how H1N1 spreads through communities and who gets the worst infection. Seasonal influenza tends to cause more serious illness in seniors as well as very young children. H1N1, on the contrary, cause more serious illness in children and young adults, as well as in pregnant women. Those who have underlying medical conditions as well as weakened immune system are also more susceptible to H1N1 infection.

As a result, the first ones to receive this H1N1 vaccine should be young children over six months of age, pregnant women, children and adults who have underlying medical conditions or weakened immune system, as well as family members caring for them. Healthy adults should receive this vaccine also because we donʼt know who will get very sick. There are many adults in North America and around the world who have no previously known medical condition and got very sick and died from H1N1 infection.

If we have a large proportion of people getting the H1N1 vaccine, and develop antibodies to this virus, it will limit the spread of H1N1: this is called herd immunity. Otherwise, all of our other measures to prevent the spread of this virus will not be as effective, and the pandemic will continue for a longer period of time.

I should mention here that we also need the seasonal flu shot. Influenza infections always come in waves. Although H1N1 will continue to dominate the winter flu season, other viruses as well as other influenza strains will spread around the country. It is important for all of us to continue to get the seasonal flu shot. Please tune into announcements from your provincial health officers. They have the most up to date and accurate information that you can trust.