Two persons from Darjeeling and Jalpaiguri who were administered the first dose of Covishield on Monday have passed away though there is no evidence yet to suggest that the deaths were related to the vaccine.

The state health department has started an investigation into the cause of deaths. A preliminary probe suggests that “vaccination is unlikely to be responsible for such sudden deaths”, said the state’s director of health services, Ajay Chakraborty.

“There were pre-existing cardiac diseases in both the persons, which frequently causes sudden death in this age group. However, since both the persons were vaccinated against Covid prior to the onset of symptoms we need final confirmation and causality analysis,” he said.

Parul Dutta, 75, from Darjeeling, had received her first dose around 3.30pm on Monday. Dutta went home without any complaints. “She came back to the health centre around 6pm with bouts of diarrhoea and uneasiness. She was referred to North Bengal Medical College and Hospital at 7.30pm,” Chakraborty said. “She passed away at 9.30pm.”

Chakraborty said that the woman was under treatment for “atrial fibrillation for quite long time”. A doctor with a state government hospital said atrial fibrillation meant that the beating of the heart was faster than usual. Such a condition can disrupt the normal functioning of the heart.

The second person who died, Krishna Dutta, 65, of Jalpaiguri, received the first dose around 10.50am on Monday and went back without any complaints. “He had vomited at 4.30pm. Around 5am on Tuesday, he developed sudden breathlessness. He passed away in his home within half and hour, before getting medical assistance,” Chakraborty said.

“He suffered from multiple cardiac problems, including cardiomegaly and cardiac muscle fibrosis, suggestive of old infarction,” he said.

Cardiomegaly is a condition where the muscle of the heart gets thicker and the chamber inside gets narrower. Cardiac muscle fibrosis is damage of the cardiac muscles.

The doctor with the state government hospital said that both the conditions can disrupt the normal functioning of the heart and can cause death.

The man also had hypertension — high blood pressure — for last five or six years, Chakraborty said.

Both of them had received the Covishield vaccine, which has been developed by Oxford University and AstraZeneca and manufactured in India by the Serum Institute of India.

The state health department has referred both cases to a causality assessment committee that was already in place for Covid-19 vaccination and other routine immunisations.