Now that the flu season is coming to an end in Canada, many public health officials will be taking a look back to reflect on the year to see what went right and what went wrong. For them, the past six months may be considered as close to an annus horribilis as one could expect. Upon closer inspection of the details, the problems deal more with unforeseen circumstances than error.
First, before the flu season had even started, a study looking at the effect of the vaccine over eight seasons suggested continued jabs could actually leave a person less likely to combat the virus. The results revealed a higher level of protection in people who had not received a vaccine for the previous five years. This concept, called vaccine interference, suggested a lag in between flu shots could improve the ability of the vaccine to prevent infection. That being said, even with interference, the vaccine would still provide sufficient immune training to those who got it; provided of course if the strains in the shot matched those circulating.
This past flu season, that last parameter was not entirely met as the composition of the vaccine missed one of the circulating strains. This in part led to a dramatic increase in the number of people showing up at hospitals near the end of last year. When vaccine performance was calculated, to no one's surprise, it was low. Getting a shot this past season meant little to no protection against that particular strain.
The final piece of bad news came from a study published last week examining the actual risk of catching the flu. The results revealed after the age of 30, we may only catch the flu twice a decade. Although this study focused on China, not Canada, and dealt with only one of the two major types of influenza, H3N2, the message was nonetheless problematic. The flu was causing far less impact than we thought and vaccines may not be as necessary as we are told.
With all the bad news coming out, one might wonder whether the flu shot is even worth the effort. The argument over the use of vaccines is already heated thanks in part to the recent outbreaks of measles in North America. These reports only appear to add fuel to the fire and put all the work of public health officials, researchers and proponents at risk.
But is it all bad news? Not entirely. This year may not have been a stellar one but it is surely not one to forget. The accumulation of information gained reveals we are going in the right direction although not perfectly.
When vaccines were first introduced en masse, the aim was to provide the immune system with training so it can effectively fight off an infection. The first products focused on easy to hit targets like measles, mumps, rubella, polio, pertussis and tetanus. A series of a few shots did the trick to protect the majority of people. Granted, some who received the shot were not completely immune and others simply could not get the shots due to pre-existing conditions. For the most part, though, vaccines helped to significantly reduce the burden of these pathogens on our lives.
In stark contrast to these viruses, influenza is a very different organism as it is a moving target. The virus has the ability to evolve in two ways, both of which can invalidate any vaccination attempt. To counter the actions in nature, public health officials in concert with the World Health Organization work hard each year to develop a worthy candidate. Admittedly, they are not always perfect but they do a very good job. Though they missed one strain (H3N2) this year, they were right on the others (H1N1, B) meaning there would be fewer infected by these particular strains.
But looking at a vaccine alone is not enough. To ensure we know what is happening, we need to look at the immune system as well. The long-term studies have done just that by taking into account the vaccine as well as natural infection. What has been uncovered is a fascinating mechanism of pathogen defence and remembrance.
When we become vaccinated or infected, our bodies develop not only an immune reaction but also memory such that we can fight off future infections. The earliest infection will lead to the strongest response as well as the longest memory. This is one of the reasons for making sure children are vaccinated in order to establish both a strong response and lasting memory.
After this, however, the situation tends to change. The next infections or vaccinations also develop responses but they may be weaker by a few per cent each time. Our memories may also be shorter, fading over a period of about five years. Without continued stimulation either through vaccination or exposure to the virus, we can lose out on our memory leaving us vulnerable.
The analysis of the infection and memory study suggest we may not need the vaccine every year, but perhaps every five. But the numbers really apply only to one type of the virus, H3N2. Considering there are three major strains of influenza (H3N2, H1N1, B), the expected flu attack rate and resultant need for memory is much higher. Young people can expect to be infected every year while older individuals can expect to fall ill about once every two years. Getting an annual vaccine, even if it is a little weaker in effectiveness, can still provide that boost to help reduce the chances of infection.
So, while the news may appear to be disastrous, the reality is there is more good than bad. We now know flu vaccination is a give and take scenario. While we may give a little in terms of overall protection each year, we can take in the confidence of a boosted the immune system to fight off any infections. Considering the virus continues to infect millions of Canadians each year, the flu shot is still worthwhile and should continue to be a significant part of our public health system.