"We are still waiting for confirmation on whether it's Priorix," a spokeswoman told Dow Jones Newswires.
Priorix is a vaccine administered to children to immunize them against measles, mumps and rubella.
Earlier Friday, a report by the Associated Press quoting Vietnamese authorities said the six children were among more than 100 children in a district of Ho Chi Minh City who were given Priorix.
The GlaxoSmithKline spokeswoman said the Vietnamese authorities have suspended the use of all types of this vaccine, also known as MMR.
"Priorix has been on the market since 1997 and no similar events have ever been reported. The safety record of Priorix would lead us to believe it was not our vaccination," the spokeswoman added.
MMR vaccines contain a mixture of live, but weakened viruses, and work by provoking the body's immune response, without causing the diseases.
This vaccine is given in two doses as part of the childhood vaccination schedule.
There have been several media reports over a possible link between the vaccine and autism or bowel disease.
The U.K. Medical Research Council, after reviewing current evidence and research, has concluded there is no link between the MMR vaccine and these disorders.
GlaxoSmithKline shares closed down five pence, or 0.3%, at 1,521 pence in London.