The five healthy volunteers, who were given a shot of Bharat Biotech International Limited’s Covid-19 vaccine at Sola Civil Hospital in Gujarat’s Ahmedabad, have not complained of any health issues so far, a senior doctor said on Friday. During phase 3 clinical trials of Covaxin, the first dose of the shot was given to the five volunteers, including a woman.

Dr Parul Bhatt, the medical superintendent of the hospital, said the second dose will now be given after 28 days. “Volunteers who’ve been vaccinated have yet not complained of any health issues/symptoms. More will be vaccinated today,” Bhatt was quoted as saying by news agency ANI.

The large-scale phase 3 trials of Covaxin, which is being developed by the Hyderabad-based firm Bharat Biotech in collaboration with the Indian Council of Medical Research (ICMR), will recruit over 26,000 volunteers from 25 trial sites across the country.

Vaccine candidates have to be tested on animal models first to check their safety and immune response. In humans, a small phase 1 trial is done to check the safety of the compound, while in phase 2, trials are done to see the immune response and the dose at which the vaccine should be administered. Large scale phase 3 trials are done to see how many infections or severe disease the vaccine prevents in a given population.

“In the first phase, we have planned to cover 1,000 healthy volunteers. They must be in the age group of 18 to 60 and with no history of coronavirus infection. Anyone who fulfils the criteria can approach us and enrol as a volunteer,” Bhatt had said on Thursday, according to PTI.

She said that doctors at the hospital engaged in the clinical trial exercise will remain in touch with the volunteers over the phone to monitor their health condition after the vaccine is administered. The senior doctor had said that volunteers will be called at the hospital at regular intervals for follow-up procedures and tests, including blood test and oxygen level.

“This whole exercise will continue for 12 months. We will also give a contact number to the volunteers in case they need any urgent intervention. The hospital will provide necessary treatment in case of any complication,” she added.

Ahmedabad’s Sola Civil Hospital is among 130 centres across the country selected for Covaxin’s phase three trials, HG Koshia, commissioner of the Gujarat Food and Drug Control Administration (FDCA), said. Bharat Biotech had last week announced the commencement of the third phase trials, the first candidate in India to reach this stage.

Four vaccine candidates from around the world have announced preliminary reports – trial data from US Pfizer and Moderna and Russian Sputnik V show their vaccines were about 95% effective at preventing Covid-19, while AstraZeneca-Oxford University said its vaccine could be up to 90% effective with a particular half dose first and a full dose later. ZyCovD, which has been developed by Indian pharmaceutical company Zydus, is also in advanced stages of human trials.