Multiple vaccinations have not been a cause of ill health in UK service personnel deployed to Iraq, finds a study published on bmj.com today.
The report from researchers at Kings College London says "recall bias" is to blame, when people link a perception of ill health with their memory of having had multiple vaccinations.
The findings add to the ongoing debate surrounding the impact multiple vaccinations may have had on the health of Gulf war veterans after the 1991 war. Several studies have found an association between self-reported multiple vaccinations in service personnel deployed to the Gulf war and later ill-health. However, other studies have not found these associations.
Dominic Murphy and colleagues randomly selected 4882 military personnel with a median age of 32 who had all been to Iraq since 2003. Before being deployed to Iraq, tetanus, typhoid and yellow fever were all routinely administered to service personnel, and anthrax was offered to individuals who had to sign a consent form.
With the use of detailed questionnaires they asked them about the maximum number of vaccinations they had received in any one day in preparation for deployment. They then randomly selected and assessed the medical health records of 10% of the group in order to see if multiple vaccinations had resulted in any adverse health effects being reported at the time.
They found "significant associations" between service personnel recalling two or more vaccinations in one day and complaints of fatigue, common mental disorders and a variety of physical symptoms.
However, when they looked at the medical records of 10% of the group they found, without exception, that there were no health differences in those who had received one vaccination and those who had received multiple vaccinations. Significantly this 10% had, like the entire group, also been more likely to report ill health if they recalled having had two or more vaccinations in one day.
The researchers say that military personnel's memories of the number of vaccinations received in a day "cannot be considered reliable," unless they had only one vaccination, which they remembered correctly.
In view of these findings and the impact of "recall bias" the researchers say "there is no evidence that receiving multiple vaccinations has resulted in adverse health for UK service personnel deployed to Iraq since 2003."