LONDON (Reuters Health) - Giving travellers a battery of vaccines at one time, rather than spreading them out over several weeks, causes no serious side effects and appears to be acceptable to most patients, according to a new study.

Although administering multiple vaccines in this way does appear to increase the risk of minor side effects, researchers from the University of Munich found most complaints related only to local soreness, tiredness or headaches.

The findings are important because the boom in last-minute travel has made it difficult to ensure travellers complete vaccine schedules that can sometimes be spread over several weeks, they say in the March-April edition of the Journal of Travel Medicine.

Recent studies suggest around one in five people flying to areas affected by diseases such as yellow fever and typhoid now plan their trips less than two weeks before departure.

As a result, physicians sometimes need to immunise holidaymakers with several vaccines at the same time, even though there are limited data on the safety of multiple travel shots.

To gauge the extent of adverse reactions, a team of researchers led by Dr. Nicole Borner studied more than 1,000 healthy travellers who visited a travel health clinic to be vaccinated before departure.

During the nine-month study, researchers immunised volunteers with between one and six vaccines. Each was then asked to complete a questionnaire detailing the type and severity of reactions they suffered.

The researchers found that 59 percent of 777 travellers who received multiple vaccinations reported adverse reactions, compared to about 43 percent of the 258 patients who were given a single vaccination.

A closer analysis showed that local and systemic side effects increased with the number of vaccinations given, with 58 percent of those who got two vaccines reporting adverse reactions, compared to nearly 61 percent of those given three. And about 70 percent of those who got more than three shots at one time reported having adverse reactions.

The most frequent reaction was pain at the site of the injection but almost 25 percent of the multi-jab group also complained of tiredness or exhaustion, compared to 14 percent of the single-shot recipients.

The study proves there is a "convincingly low level" of side effects for multiple vaccinations in travellers, according to Borner's team.

"Vaccinees who receive multiple simultaneous vaccinations due to lack of time will objectively experience more side effects. However, results show that vaccinees reported little subjective impediments," they write.

"These findings may increase the acceptance of multiple vaccinations given to travellers."

SOURCE: Journal of Travel Medicine 2003;10:112-116.

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