Some research has pointed the finger at pig gelatin stabilisers or residual mice proteins in the vaccine as the cause of these responses.
The test vaccine, delivered in two shots, is based on a purified but inactivated virus, grown in lab-dish cells, to prime the immune system.
It is a promising candidate for travellers at risk and should be further studied for use among children in endemic countries, said Marc Fischer of the CDC and colleagues in a commentary also carried by The Lancet.
An alternative, Chinese-made vaccine, based on virus grown in hamster cells, is also increasingly being used against the disease.
Several Asian countries have licensed it, including Nepal and India, which used it to vaccinate 30 million children in 2006 and 2007. The Chinese formula needs fewer doses and is less expensive and easier to produce than the mouse-derived vaccine.
Source-AFP
KAR/P