Science

H1N109 vaccination - what the public should really know

Professor Robert Booy, Children's Hospital at Westmead, University of Sydney

28 January 2010

“As the public clamour has risen for recouping funds spent on treating or preventing the new pandemic swine flu and interested parties have said "I told you so" in relation to the relative mildness of disease, I have become more and more concerned that the imperative of public health is being overshadowed. The questioning of the value of H1N1 2009 vaccines by experts from different fields has undoubtedly been done in good faith but may well also have sounded the death-knell for what would otherwise have been, for the first time in history, the eminently achievable control of a pandemic virus with attendant dramatic reductions in transmission, disease and deaths. Many people returned from trips to the northern hemisphere during January, some bringing the swine flu virus with them and now that children are returning to school the risk of transmission rises greatly. Europe USA and Asia have already had a second wave and ours is coming, perhaps as soon as February.

The double truth that the pandemic H1N1 2009 virus was by and large innocuous in the great majority of those infected but could, in a small percentage, be severe remains the case and was predicted to be so from the outset in April 2009. A small percentage of a very large number of infected people can still lead to a sizeable and important number of seriously infected people as demonstrated by intensive care units full to capacity across developed countries beginning for example in Australia from June 2009.

These admissions to intensive care have been almost entirely in people aged below 60 years of age, a large proportion of whom, perhaps a third, had no underlying medical risk factor. Herein lies another duality that is surprising to many. The main reason any new pandemic is predicted to cause large numbers of deaths is because all in the population are new to the virus, and the elderly, being particularly vulnerable, constitute by far the greatest proportion of fatalities. With the current virus, there is evidence from Australia, North America, Asia and Europe for cross protective immunity in the elderly which is especially strong in those aged in their 80s and 90s and likely to have been exposed for the first time in early childhood to an influenza virus similar to the 1918 (or the same) pandemic virus.

The WHO continues to assess the impact of this pandemic as moderate and emphasize that it will not be possible to have an accurate understanding of casualty rates until at least a year after it has peaked, although we know already that influenza deaths in children and young adults have been higher than in recent memory.

Mathematical modelling had been usefully applied to this and other infectious disease problems. If a virus on average affects 2 people for every individual infected, its effective reproduction number (R) is 2 and it can be logically derived that at least 50% of the population must be immune to control an outbreak and lead to its extinction. The formula for the proportion needed to be immune is 1 minus (1 divided by R). The H1N1 2009 virus has an effective R closer to 1.5, so as an approximation we need at least one third of people to be immune for control. The proportion is however higher in certain crowded situations such as children in day care or schools as transmissibility is also higher in those situations.

There are reports from countries suggesting that uptake of the new vaccine for H1N1 2009 may be somewhere between 10 - 20% of the population. Almost all are likely to be immune as a consequence. If about 20% are also immune due to infection, then we may well not have enough population-wide protection to prevent the next wave, particularly in high risk settings like schools and kindergartens.

The more I learn, the more I understand how much I don't know. What is more, as an epidemiologist, the biggest lesson I have learnt is not to jump to conclusions but to search for those alternate explanations, those confounders which deepen understanding and should inform public health policy and practice. My perspective lies in the clinical and public health realms. My concern about well intentioned skeptics is that what seems a compelling argument to them (and some other people) may be confounded.

If I had an injury involving a severe laceration/amputation of a finger, I would much prefer a hand surgeon to neurosurgeon; both are highly trained and very much of it is overlapping, but at the end of the day I want the expert who does hand surgeries every day to look after me - he or she knows more about the topic and has the practical expertise.

I, as a doctor, am vaccinated against H1N1 2009 so that I am protected and do not pass on the infection to vulnerable patients . The vaccine is safe and effective. My nearest and dearest have been vaccinated too. Why not you?”

Addendum: Prof Robert Booy is a Paediatrician and infectious diseases expert, Children’s Hospital at Westmead, University of Sydney.

He does not hold shares in vaccine companies and does not accept payment from them for consultation. For some years he has produced educational material for the public and health professionals on a pro bono basis. He does vaccine research trials with government and industry.
He has been a vaccine researcher for over 20 years, the last 10 focusing on influenza. He is the author of over 25 scientific publications on influenza and a member of national committees devoted to influenza pandemic planning and response.

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