It's the influenza virus, a.k.a. "the flu."
In response, public health officials are promoting flu shots and clinics are springing up. In Ontario, the vaccinations are free for everyone for the second year running.
But is it any more than a shot in the dark?
Health officials admit that it's impossible to predict with certainty what strain of the virus will attack in a given year, that new mutations may occur, and a completely unknown strain could cause a worldwide pandemic at any time.
With a population increasingly inclined to embrace more "natural" therapies and exposed to anti-immunization information from a variety of sources, not the least of which is the Internet, there's more than a little skepticism about the value of flu shots.
Dr. Carolyn Dean, a medical doctor who also holds a degree in naturopathic medicine, does not totally discount the value of shots but maintains it depends on individual need. In people vulnerable to flu complications – seniors, those with chronic conditions or illnesses such as diabetes, or whose immune systems have been compromised by drugs or disease – the shots may well be necessary, she says.
"Flu can lead to pneumonia and definitely can lead to morbidity and mortality. So, if someone came in with a history or lots of colds and flu and remedies weren't working to boost the immune system, that might be a possibility.
"But to issue a blanket statement that everyone over a certain age should get it, I really don't like the sound of that."
Dean, who says her interest in naturopathic medicine stems from her doctor's oath to "do no harm," is concerned about side effects from putting too many foreign or chemical substances into the body.
"I'll always be a proponent of alternatives but, being a medical doctor, I know that at a certain point drugs and surgery are necessary. People will do just fine with them if they haven't built up a resistance to them and they're not already chemically overloaded.
"We are living in a society where it's been reported that there are up to 500 different foreign chemicals that can be measured in the cells of our bodies. Whose to say that flu shot isn't the straw that breaks the camel's back?"
For people who have no special needs, the author of Dr. Carolyn Dean's Natural Prescriptions for Common Ailments recommends taking the natural route first.
"I know from my training that there are many, many options and choices for boosting the immune system and preventing illness and for treating colds and flu other than resorting to a shot." Such things include getting plenty of sleep, eating nutritiously and not overeating, and limiting such things as sugar ("the amount in two cans of soda can suppress the immune system or paralyze it for four to five hours").
"It's important to follow those good health measures but if you really want to definitively prevent the influenza, the best way to do it is through a vaccine," says Dr. Ian Gemmill, chairman of the Canadian Coalition for Influenza Immunization and medical officer of health for the Kingston, Ont. region. "If there is an onslaught from a virulent influenza, no matter how healthy you are and try to be, there's a very good possibility you might become sick."
With 5,000 to 6,000 deaths each year from the flu or its complications, he advocates the shots for everyone and particularly for those at greatest risk of developing a serious illness or complication such as pneumonia.
Gemmill says it's important to differentiate between true influenza and the extended colds or upper-respiratory infections that people come down with each year. "If you've got the flu, you take to your bed," he says. "You feel like you've been hit by a truck and you just don't want to do anything."
Symptoms include fever, sore throat and headache but definitive of the flu are the muscle and joint aches and pains that can be intense. Any many who have influenza continue to suffer from fatigue for several weeks before they are truly back on their feet.
Gemmill also discounts the possibility of side effects, saying that in clinical studies there was virtually no difference in the incidence between those receiving the flu shot and the placebo control group. The most commonly reported effect was pain at the injection site "which is not because of the vaccine but because you got a needle."
In terms of chronic conditions that people have linked to the vaccine, he says none have been proved. He allows that some people may experience some flu-like symptoms, including fever, following the vaccination but maintains "it's certainly far less traumatic than getting the flu and it does not tend to recur ... I think the balance is to look at the risks versus the benefits ... There's no safety reason not to get it and every benefit to getting it.
"It's a small investment ($10 to $15 in most of the country and free in Ontario). There are other ways of dealing with the flu, treating it and preventing it, but this is by far the most cost-effective and longest-lasting prevention we've got."
While he admits that each year the World Health Organization survey of worldwide flu systems that determines the content of the vaccine is really an "educated guess" at what strain will cause problems, Gemmill says it's right 14 out of 15 times. Occasionally a mutation, like the Sydney strain in 1997, takes everyone by surprise but those who have been vaccinated are likely to be at least partially protected even in those cases.
A profound reconfiguration of the virus can result in a global pandemic, as happened in 1918-19 with the Spanish flu and again in 1957-58 and 1968-69 with the Asian/Hong Kong strains. This phenomenon, says Gemmill, cycles every 30 to 40 years so world health officials are bracing for another soon. However, he says, universal vaccination programs ¬provide a valuable model for inoculating thousands of people in a short time period.