The National Institutes of Health (NIH), the primary agency of the United States government for biomedical and public health research, has said that Bharat Biotech's COVAXIN, India's first indigenously developed Covid-19 vaccine, is a "highly efficacious" jab.

The vaccine is developed by Hyderabad-based Bharat Biotech in collaboration with Indian Council of Medical Research (ICMR).

The NIH said that the adjuvant used in COVAXIN, Alhydroxiquim-II, was discovered and tested in the laboratory by the US biotech company ViroVax with support exclusively from the NIH's NIAID Adjuvant Development Program.

Adjuvants are substances formulated as part of a vaccine to boost immune responses and enhance a vaccine’s effectiveness.

The NIH said that the adjuvant developed with funding from the agency has "contributed to the success of the highly efficacious COVAXIN COVID-19 vaccine, which roughly 25 million people have received to date in India and elsewhere".

“Ending a global pandemic requires a global response,” said Anthony S Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), which is a part of NIH.

“I am pleased that a novel vaccine adjuvant developed in the United States with NIAID support is part of an efficacious COVID-19 vaccine available to people in India," he added.

"The adjuvant comprises a small molecule attached in a unique way to Alhydrogel, a substance frequently called alum that is the most commonly used adjuvant in vaccines for people. Alhydroxiquim-II travels to lymph nodes, where the small molecule detaches from alum and activates two cellular receptors. These receptors, TLR7 and TLR8, play a vital role in the immune response to viruses," the NIH said in a statement on Tuesday (29 June).

Alhydroxiquim-II is the first adjuvant in an authorized vaccine against an infectious disease to activate TLR7 and TLR8. In addition, the alum in Alhydroxiquim-II stimulates the immune system to search for an invading pathogen, it added.

Molecules that activate TLR receptors stimulate the immune system powerfully, but the side effects of Alhydroxiquim-II are mild. This is because, after COVAXIN is injected, the adjuvant travels directly to nearby lymph nodes, which contain white blood cells that play an essential role in identifying pathogens and fighting infection.

Consequently, only a small amount of Alhydroxiquim-II is needed in each dose of vaccine, and the adjuvant does not circulate throughout the body, thereby averting more widespread inflammation and undesirable side effects, the agency said.

Citing the phase 2 clinical trial results of COVAXIN, the NIH said that the vaccine is "safe and well tolerated".

Meanwhile, unpublished interim results from the Phase 3 trial indicate that the vaccine has 78 per cent efficacy against symptomatic disease, 100 per cent efficacy against severe COVID-19, including hospitalization, and 70 per cent efficacy against asymptomatic infection with SARS-CoV-2, the virus that causes COVID-19, the NIH said.

Further, the NIH said that results from two studies of blood serum from people who had received COVAXIN suggest that the vaccine generates antibodies that effectively neutralise the B.1.1.7 (Alpha) and B.1.617 (Delta) variants of SARS-CoV-2.