A reduced dose of flu vaccine can still give full immunity, according to a study done in healthy young women. This opens up the possibility of extending the supply of flu vaccine to offer coverage to more of the population.

 Summary

A new study shows that a half dose of flu vaccine is as effective as a full dose, at least in a population of healthy young women. As we face the prospect of pandemic flu, it is good to know that supplies can be stretched further to protect more of the population.

Introduction

It is the flu season and, for many people, having a flu jab is an essential part of keeping well. Those with heart and lung problems, and the elderly, are especially vulnerable to the complications of flu and should be sure they are protected. But what about the supply? In 2004, there was an abrupt loss of about half the national supply because of technical problems. If a pandemic strain emerges, we will need mass vaccination and the supplies must be enough to go round. The dose needs to be enough to produce sufficient antibody response to afford protection. But how small a dose can we get away with to protect the person?

What was done

Researchers at the Walter Reed Army Medical Center, Washington DC, gave either a full or a half dose of flu vaccine to a group of healthy adults aged between 18 and 65, dividing them into two groups ((under 50, over 50). They then measured their antibody response to the vaccine.

What was found

Response to half dose vaccine was not substantially less than to full dose vaccine, particularly in the younger age group. Women of all ages responded better to both doses than men. Indeed, women on a half dose responded as well as men on a full dose.

What this study means

These findings have implications for flu vaccine supply. During a shortage, doctors could take age and sex into account when considering what dose to give. Reduced doses among young women might help make the supply of vaccine go further, whilst still affording them the protection they need.

Source

Half versus full dose trivalent inactivated influenza vaccine (2004-2005) RJ. Engler, MR. Nelson,  et al., Archives of Internal Medicine, December 8/22 2008, vol. 168, pp. 2405--2414