The problem isn’t just “out there,” it’s also “in here”

Giddings1 suggests that Canada might benefit from a harmonized national vaccination initiative focused on increasing vaccine coverage. I’d like to suggest alternatives.

Although the effect of vaccine hesitancy on particular subpopulations is unequivocal, I do not think that a national policy aimed at decreasing vaccine hesitancy, and ultimately increasing vaccine coverage, will be the leverage point that Giddings1 hopes.

We assume that the cause of the problem is “out there” (e.g., parents who are hesitant to vaccinate their children), and not “in here” (e.g., policy decisions).2^,3 When we lose sight of the connections between top-down vaccination programs and the bottom-up immune response of an individual, we can expect to be surprised.

Heffernan and Keeling4 show that measles vaccination has intended as well as unintended effects. Measles vaccination reduces the susceptible population as well as the incidence of disease (this is the intended effect — the one we claim credit for), but it also prevents the virus from circulating and thus prevents natural boosting. In the face of high vaccine coverage (i.e., > 70%), population immunity wanes slowly, and susceptibles replenish over time. The whole system balances uneasily near outbreak conditions (this is the unintended effect — the one that surprises). The final trigger is the introduction of infected individuals.

I am not opposed to a harmonized national solution, but it will require more thought than simply increasing vaccination coverage. Effective policies will need to creatively balance population-specific goals with an individual’s requisites for life-long immunity.