India is set to evaluate a combination of the homegrown Covid-19 vaccine Covaxin with a candidate intranasal vaccine designed by US researchers under the expectation that the two vaccines in sequence might enhance protective efficacy against the infection.

An expert panel with India’s regulatory authority for drugs and vaccines has approved a clinical trial that will involve Covaxin as the first dose on day zero and the candidate intranasal vaccine based on a chimpanzee adenovirus as the second dose on day 28.

Bharat Biotech, the Hyderabad-based maker of Covaxin, plans to conduct the trial combining Covaxin with the intranasal candidate vaccine developed by Michael Diamond and his colleagues at Washington University School of Medicine, St Louis, and procured by the company last year under a licencing pact.

The company is hoping that the two vaccines will through different mechanisms increase the protective efficacy against Covid-19. Covaxin, like other intra-muscular injections, stimulates an arm of the immune system called systemic immunity, while the intranasal candidate stimulates mucosal immunity.

The intranasal candidate developed at Washington University was last year the first among Covid-19 vaccine candidates to show the promise of what scientists call “sterilising immunity” — a type of immunity that prevents the virus from even establishing an infection.

The expert panel with the Central Drugs Standard Control Organisation approved the trial on Thursday after Bharat Biotech’s representatives made a presentation.

Bharat Biotech is already conducting an independent trial to evaluate the safety and immune responses triggered by the intranasal candidate in 175 volunteers to be recruited at four sites — All India Institute of Medical Sciences, Patna, Apollo Hospital, Chennai, St Theresa’s Hospital, Hyderabad, and the Gillurkar Hospital, Nagpur.

The trial will evaluate the intranasal candidate as a single dose and a double-dose vaccine. Researchers say the strategy of combining Covaxin and the intranasal candidate is driven by the expectation that the combination of systemic immunity from Covaxin and mucosal immunity from the intranasal candidate might provide superior protection against the infection.

Covaxin-Covishield

The CDSCO expert panel also on Thursday approved a trial that will mix Covaxin and Covishield as the first and second doses. Doctors at the Christian Medical College, Vellore, will conduct the Covaxin-Covishield trial.