Indian researchers have found no evidence that COVID-19 vaccination was behind "unexplained sudden deaths", a medical organisation says, instead pointing to the disease itself, binge drinking and intense exercise as risk factors.

The Indian Council of Medical Research (ICMR) conducted a study following what it called "anecdotal reports about sudden unexplained deaths among apparently healthy adults" aged 18 to 45 between October 2021 and March 2023.

"We found no evidence of a positive association of COVID-19 vaccination with unexplained sudden death among young adults," the research group said in a study published in the Indian Journal of Medical Research.

"At the same time, family history of sudden death, hospitalisation for COVID-19 and lifestyle behaviours such as recent binge drinking and vigorous-intensity physical activity were risk factors for unexplained sudden death."

ICMR researchers identified 29,171 sudden deaths and scrutinised the records of 729 of the cases as well as 2916 "control" subjects as part of their investigation, the group said.

Government data shows India suffered 45 million COVID-19 infections and 533,295 related deaths but experts say the actual numbers are several times higher.

Many Indian hospitals ran out of beds during the peak of the COVID crisis and many people died at home.