A half-dose flu shot may be just as effective as a full dose for healthy people under 50 years of age, suggests a new study, which could be helpful during times of vaccine shortage.

The study of more than 1,000 subjects, published in the Archives of Internal Medicine, found that those who received the half-dose vaccine produced a similar immune response to the flu compared to those who received the full-dose vaccine.

The research, conducted by a team from the Walter Reed Army Medical Center in Washington, D.C., also found that rates of doctor visits for respiratory and cardiovascular problems were similar among those who received the full- and half-dose vaccine.

"Given the benefits of immunizing healthy working adults and caregivers, these data support the validity of a dose reduction strategy in the setting of vaccine shortages," the authors concluded.

According to background information included with the study, health-care facilities in the United States have experienced vaccine shortages since 2002. A similar problem has not yet occurred in Canada, however the shortage has led researchers to consider the possibility of reducing the dose for healthy individuals.

"Reduced dosing could have a significant impact on the response to vaccine shortages, particularly at a local level when faced with considerable delays in vaccine supply delivery," the authors wrote.

Health-care professionals could further alleviate vaccine shortages by offering the half-dose flu shot to more women, the study found.

According to the findings, women of all age groups (study subjects ranged from 18 to 64) produced similar immune responses to men who received a full dose.

Another benefit of the study could be an increase in the number of people who get the flu vaccine. The half-dose flu shot was associated with fewer side effects, which may make the vaccine more palatable to those who have previously experienced harsh reactions.

Public health agencies have increased awareness programs for the flu and the flu shot in recent years.

The Public Health Agency of Canada advises that anyone over six months of age who has not had a previous severe allergic reaction get the flu shot.

In particular, it advises that pregnant women, children, those with chronic diseases, senior citizens, health professionals and caregivers to get the shot.

Given that the vaccine changes each year in an attempt to match the three flu stains experts believe will be in circulation that season, it is important to get vaccinated every year, the agency says.

According to the agency, flu vaccination programs have reduced the overall risk of infection by up to 60 per cent since the 2003-2004 flu season.