When you take your child to get her flu vaccine this year – which you should, provided she is over 6 months old – you will likely not be given the choice between the shot and the spray. The reason why requires us to talk a bit about how flu vaccine efficacy is measured – and it may not be quite what you think.
I'm diving into these shark-infested waters today thanks to a study appearing in Annals of Internal Medicine that evaluated a live, attenuated intranasal flu vaccine versus an inactivated injectable vaccine in what was a very elegant randomized trial. Let's take that study first, and then I'll tell you why you won't get the spray this year.
Researchers in Canada wanted to assess whether herd-immunity would be enhanced more by the nasal versus injectable vaccine. Super tricky to do in this modern world, as you might imagine, as the "herd" is really quite large, so they found some places where the herd was smaller. Specifically, Hutterite communities:
Hutterites are an ethno-religious anabaptist group that lives in small groups of about 100 people. Largely self-sufficient, these colonies have infrequent contact with the outside world and are thus a perfect environment to study herd immunity.
58 communities were enrolled in the study, and were randomized at the community level to have their children get the spray or the shot. This is called cluster-randomization and there is really no other way to do a study like this.
Over three years, they traced the ebbs and flows of influenza infection, and found that, basically, the rates of flu were the same- around 5% regardless of whether it was a spray or shot community.
So why won't you get the spray?
Because last flu season, in the US at least, the spray didn't seem to work:
What this slide shows, aside from the fact that the CDC needs to hire better graphic designers, is that, in the 2015-2016 flu season, the live attenuated vaccine was ineffective while the shot provided good protection.
Now, measuring vaccine efficacy is a bit weird because the CDC is not doing randomized trials of vaccines every year. Rather they do a sort of case-control study, looking at the percentage of people with flu who got vaccinated compared to the background vaccination rate.
Does this Annals study refute last year's findings?
The answer is that it's incomparable. We can't calculate vaccine efficacy in this study because the background vaccination rate is not in any way random. All the kids got some vaccine. I will point out that the influenza infection rate among the vaccinated kids, around 6% is actually a bit higher than the infection rate among the unvaccinated adults (5%).
But comparing infection rates in kids to adults is a total apples and oranges situation.
So no, this study won't change the American Academy of Pediatrics mind on the issue. Your little one is getting a shot:
There may be a few more tears in doctor's offices this flu season, but with luck, fewer cases of flu.