Who should be vaccinated against the flu first?

If there isn’t yet enough vaccine to round, who should get priority?

It’s an old question, with some old answers:

• Women and children first. (The sinking ship analogy, along with consideration for unlived lives.)
• The very young and the very old. (Most likely to die due to undeveloped or compromised immune systems)
• Health care workers and emergency services. (Most severe consequences for other people if they are sick).

The objective (which I think most people can agree on) is to save the greatest number of life-years. Thus, if the risk of death is the same, we should give a virus in limited quantities to the youngest first, who can be expected to have more years to live. We should also prioritize the most at-risk groups.

There is of, course, an edge case here: if the very young cannot fend for themselves if their parents die, then we should give a vaccine to the parents first. (If you read the safety instructions for an aircraft, you will note that people should put on their own oxygen masks before helping their children: the reasoning is the same).

But just because these answers seem obvious, it doesn’t mean they are correct. A very interesting paper has recently been published by Medlock & Galvani on Optimizing Influenza Vaccine Distribution.

The reasoning behind these simple answers fail to recognize some key differences between a pandemic and other life-threatening risks. In particular, they do not take account of the effects of virus transmission and vaccine efficacy.

Jan Medlock and Alison Galvani’s paper looked at flu vaccination from an epidemiology perspective taking these key factors into account. They used estimated parameters from previous flu pandemics (1957 and 1918) and a models of flu transmission which took into account the relationship between the age of a person and their likely number of contacts.

Their interesting conclusion is that if sufficient vaccine is available the vaccination of the principal flu transmitters (school age children and their parents) should be given priority if the most years-of-life-lived are to be saved or the greatest number of flu deaths averted.

Unfortunately it’s not an answer that I can see being sold to the public at large by politicians.

The original published paper is sadly behind a paywall, but you can find out more details and background information from some other publications of the authors:

• Medlock, J and Galvani, A.P., Optimizing Influenza Vaccine Distribution, Workshop on Economic Epidemiology in Kampala, Uganda, 2009.
• Galvani, A.P., Reluga, T.C., and Chapman, G.B. Long-standing Influenza Vaccination Policy is in Accord with Individual Self-interest but not with the Utilitarian Optimum. Proceedings of the National Academy of Sciences USA 104: 5692-5697, 2007