As a particularly nasty flu season rages on, and the deaths of children continue to make headlines, one question arises repeatedly: How effective is the flu vaccine?
That's not a simple question to answer.
The effectiveness of the vaccine depends on what strains of the flu are circulating, how virulent they are, how well the vaccine matches to the circulating strains and, finally, how much protection it provides against those strains.
So let's look at each of those challenges in turn.
Every year, scientists gather and try to divine which strains will be predominant in the coming season. The vaccine is prepared based on that judgment.
This year's flu shot was designed to protect against influenza A/H3N2/Hong Kong, A/H1N1/Michigan and B/Brisbane. Flu season begins in the Southern Hemisphere and then we get a sense of whether the guesswork was accurate.
Australia was hit hard by the flu in 2017, with a high number of deaths and hospitalizations. H3N2 was the dominant circulating strain, but the vaccine provided little protection – only about 10 per cent.
Scientists have known for many years that the flu vaccine works poorly against H3N2 strains, but it's not clear why.
What was clear, as early as June, was that we would be in for a nasty flu season in the Northern Hemisphere. But little was done to prepare.
What we are seeing today – low vaccination rates, overflowing emergency rooms and overcrowded hospitals – is a direct result of that lack of preparation.
Studies in Canada and the United States have shown, unsurprisingly, that the vaccine is ineffective against H3N2 – 17 per cent in Canada, and 25 per cent in the United States. However, what's intriguing is that the vaccine is quite effective in protecting young children between the ages of six months to eight years against H3N2 – about 51 per cent – but almost entirely ineffective for those 9-16. Again, it's not clear why.
The flu vaccine is also working really well against H1N1 – about 67 per cent – but there is little H1N1 circulating.
The other glimmer of good news is that the flu shot works pretty well against influenza B – about 42 per cent. That's important because, in Canada, we're seeing unusually high rates of influenza B, especially in children.
(Normally, A strains circulate from November to March, then B strains, sometimes known as "spring flu," kick in).
There are many ways to crunch the numbers and when you look at the data, all strains together, the flu shot is about 39 per cent effective over all, and 59 per cent for children.
That's a far cry from the commonly stated view that the flu shot doesn't work.
That being said, we need to spend a lot less effort parsing the data and invest a lot more effort in practical measures.
Bottom line is, getting a flu shot makes a lot more sense than not getting a flu shot.
You reduce your risk of catching and spreading the flu and, even if you do get the flu, having the vaccine reduces the severity of illness and death.
Influenza is not a trifling problem.
Sure, the risk of dying from influenza is small; most people who get the flu are sick for a week or so and get better. But the flu still causes about 3,500 deaths and 12,000 hospitalizations in Canada annually, not to mention a lot of absenteeism and lost productivity.
Those most at risk of complications are the frail elderly, and those with underlying health conditions such as heart disease, cancer and chronic obstructive pulmonary disease (COPD), or a compromised immune system.
If nothing else, you should get the flu shot to protect the most vulnerable in society – the elderly, young babies and pregnant women.
Yet, only one in three adults and one in four children in Canada gets the flu vaccine. The death of children is particularly tragic and always makes headlines. There have been at least 84 child flu deaths in the United States this year, and at least eight in Canada, and this perfect storm of a flu season is far from over.
A new study, published this past week in the journal Pediatrics found that two-thirds of children who died had not been vaccinated. There is no question we need a better flu vaccine.
But the fact that the existing flu vaccine is less than perfect is no excuse to eschew it completely.
A little bit of protection is better than none at all.
The Canadian Press