New Delhi, Aug 16 : Poor surveillance data of encephalitis is affecting development of prevention and control measures to counter the deadly virus disease that has claimed lives of over 500 children this year in Uttar Pradesh, a study said Friday.

The study was conducted by the Public Health Foundation of India (PHFI) in the wake of the increasing number of Acute Encephalitis Syndrome (AES) cases in eastern Uttar Pradesh.

It reviewed AES surveillance data for January 2011 to June 2012 from Kushinagar district in the state.

During the study, it was found that the vaccination history of 84 percent of AES cases in 2011 and 100 percent in 2012 were "unknown".

"At the crux of the debate lies quality surveillance for AES, including laboratory testing, which is necessary for understanding AES, planning interventions, and developing appropriate policy measures," said Manish Kakkar of PHFI. (IANS)