“The rate of effectiveness of the flu vaccine is usually higher,” says Hélène Gingras, spokesperson for the Quebec Ministry of Health and Social Services. When the vaccine strains and those circulating perfectly match, 70% to 90% efficacy is achieved. In fact, in 2007, two of the vaccine strains were not matched with the strains that caused the most cases of influenza. In particular, the B strain of the vaccine was found to be ineffective against the circulating B strain¹.

“Despite everything, even if the effectiveness is not complete, vaccination remains the best protection for people at risk, insists Hélène Gingras. Although we know that older people, for example, do not respond as well to the vaccine as younger people whose immune systems work better. Of course, hygiene measures like hand washing and respiratory etiquette are also very important, she recalls. “But while the vaccine doesn’t always prevent an elderly person from getting the flu, it does reduce the severity and complications. It also reduces the death rate. The flu causes 1 to 000 deaths in Quebec each year, mainly among seniors. “

Until recently, the estimated reduction in the number of deaths caused by influenza in the elderly was 50% and the reduction in hospitalizations by 30%, a very good public health outcome. However, in recent years, researchers have questioned the results of the case-control studies that led to these reduction rates: these results would be skewed by a confounding factor called the “healthy patient effect” (healthy user effect)^2-8 .

“People who get vaccinated are good patients who see their doctors regularly, take their medications, exercise and eat well,” says Sumit R. Majumdar, physician and assistant professor in the Department of Public Health Sciences at the ‘University of Alberta in Edmonton. While frail older people who have difficulty moving around are more likely not to get the vaccine. “

If these factors are not taken into account in the analysis of statistical data, the results are biased, according to D^r Majumdar. “Unvaccinated people are more likely to be hospitalized or die from influenza, not because they are not vaccinated, but because their health is initially more fragile,” explains- he does.

The Canadian case-control study led by Dr.^r Majumdar and published in September 2008 took into account this important confounding factor⁸, just like a similar study conducted in the United States and published in August 2008⁷. The Canadian team examined the health records of 704 elderly people admitted to six hospitals with pneumonia, the most common and dangerous complication of the flu. Half of them were vaccinated, the other half were not.

Result: “Our study shows that the fact of being vaccinated or not has no effect on the mortality rate of people hospitalized with pneumonia,” comments D.^r Majumbar. This does not mean that these people should not be vaccinated. Rather, it means that we are not doing enough to reduce influenza in other ways. For example, there is not enough public health advertising about handwashing, a measure with much stronger evidence for effectiveness. “

The US study, published in August 2008, looked at more patients and looked at the rate of pneumonia in vaccinated and unvaccinated elderly people.⁷. The verdict is the same: the flu shot is not very effective in preventing pneumonia, which is the main complication of the flu.

The results of these two studies do not surprise D^re Maryse Guay, medical consultant at the Institut de santé publique du Québec (INSPQ)⁹. “It has been known for a long time that the vaccine is less effective in the elderly, but, for now, these two studies are insufficient compared to all the positive data that we have accumulated about the effectiveness of the vaccine. vaccine, ”she explains. She notes, among other things, that in both studies, the populations studied are very specific and that the Canadian study was conducted outside of the influenza period. “However, we are always on the lookout and scrutinize everything that is published on the issue. At worst, we vaccinate for nothing, but this vaccine, compared to others, is inexpensive and we know that it is effective in healthy people, ”she adds.

“Before spending a lot of money to increase vaccination coverage in the elderly, it is necessary to do placebo-controlled clinical studies to have a more exact idea of ​​the real rate of effectiveness of the vaccine, nevertheless says Dr.^r Majumdar. For the moment, only one study of this type has been carried out, 15 years ago, in the Netherlands: the researchers then observed an almost zero effectiveness of the vaccine. We need strong clinical evidence. “

“The clinical data are old, concedes the D^re Guay. However, since we have the impression that the vaccine is effective, these studies are not done because it would not be ethical to give a placebo. In addition, doing clinical trials on immunization against influenza is very complex, especially because the vaccine strains vary each year and we can never be sure that they will protect against those that are circulating. “

Children are the main transmitters of influenza. Their symptoms are less acute than those of adults, so parents pay less attention to them. Result: the children are not isolated and presto! mom catches it and maybe also grandpa, who lives in a residence. It does not take more to cause an outbreak in a population at risk of complications.

The D^r Majumbar uses the example of Japan to illustrate that childhood immunization should be encouraged. In this country, where there was a universal program for immunization of children at school, the rate of influenza increased among the elderly when this measure was abandoned. “It is therefore important that children in general and those around the elderly be vaccinated,” he suggests. As their immune system responds better to vaccination than that of seniors, the vaccine protects them better. If they don’t get the flu, they won’t pass it on. “

The Japanese situation cannot be extrapolated to that of Quebec or Canada, shade D^re Guay: “In Japan, contact between children and grandparents is very close and frequent, because they often live in the same house, which is not the case here. Over the past few years, we have discussed the relevance of offering the vaccine to all children in Quebec, but we are already not succeeding in sufficiently reaching the target populations, in particular people at risk and healthcare workers. “

The D^re Guay describes the situation in Ontario, which has offered a universal influenza vaccination program since 2000. According to the available data, it finds that the effect of this measure is insufficient to reduce transmission, unlike what happened in Japan. “In the United States, public health has just decided that annual influenza vaccination is recommended for children 6 months to 18 years of age. We look at what is being done elsewhere and wait to see the results obtained before making any decisions. We have used this strategy for several vaccines and so far it has been very useful to us, ”says D^re Cool

Quebec’s free vaccination program targets several categories of people at risk of complications from the flu, but also all the people around them because they live with them or because they work with them. People at risk are:

– people aged 60 and over;

– children aged 6 months to 23 months;

– people with certain chronic diseases.

• Consult our fact sheet on influenza to find out how to prevent and treat it.
• All the details about the flu shot: names of products on the market in Quebec, composition, indications, schedule, efficacy, etc.

  Quebec Immunization Protocol, Chapter 11 – Vaccines against influenza and pneumococcus, Santé et Services sociaux Québec. [PDF document consulted on September 29, 2008] publications.msss.gouv.qc.ca

• Answers to 18 questions about the flu shot

  Influenza (flu) – Frequently asked questions, Santé et Services sociaux Québec. [Accessed September 29, 2008] www.msss.gouv.qc.ca

• Comparative table of cold and flu symptoms

  Is it a cold or the flu? Canadian Coalition for Immunization Awareness and Promotion. [PDF document accessed September 29, 2008] resources.cpha.ca