New York, Jun 6 (IANS): The US Food and Drug Administration has called Novavax's protein-based vaccine effective against Covid-19, but has flagged concerns over its risk of myocarditis and pericarditis.

Myocarditis is inflammation of the heart muscle, and pericarditis is inflammation of the outer lining of the heart. In both cases, the body's immune system causes inflammation in response to an infection or some other trigger, according to the US CDC.

Vaccine NVX-CoV2373 is already being locally manufactured by the company's India partner, the Pune-based Serum Institute of India (SII) under the brand name Covovax. Media reports claimed that SII will partner with Novavax on an Omicron variant specific vaccine.

Phase-III trials have shown Novavax's jab to be 90 per cent efficacy against Covid-19, and is also approved in some countries in Europe and others. But in a trial of 30,000 patients, conducted between December 2020 and September 2021, there were four cases of myocarditis detected within 20 days of taking the protein-based shot.

"These events raise the concern for a causal association with this vaccine, similar to the association documented with mRNA COVID-19 vaccines," FDA staff wrote in its briefing documents.

While the agency requested Novavax to flag myocarditis and pericarditis as an "important identified risk" in its materials, the company disagreed. It said that natural background events of myocarditis can be expected in any sufficiently large database.

"Based on our interpretation of all the clinical data supporting NVX-CoV2373 ... we believe there is insufficient evidence to establish a causal relationship," the company said in a statement.

Besides Novavax, vaccines developed by Pfizer and Moderna have also shown risk of heart inflammation.

The FDA's Vaccines and Related Biological Products Advisory Committee will meet on June 7 to consider whether the Novavax vaccine should be authorised. If approved, it will become the fourth Covid vaccine after Pfizer, Moderna, and Johnson and Johnson.

NVX-CoV2373 was created using Novavax' recombinant nanoparticle technology to generate antigen derived from the coronavirus spike (S) protein and is formulated with Matrix-M adjuvant to enhance the immune response and stimulate high levels of neutralising antibodies. It contains purified protein antigen and can neither replicate, nor can it cause Covid-19.

The vaccine can be stored at 2 to 8 degrees Celsius, allowing the use of existing vaccine supply chain channels for its distribution. It is packaged in a ready-to-use liquid formulation in 10-dose vials.