Biotech firm Novavax disclosed Monday that it had submitted its long-awaited application to the U.S. Food and Drug Administration for an emergency use authorization for its COVID-19 vaccine in the United States.

Its vaccine, currently known as NVX-CoV2373, is made differently than the Moderna and Pfizer-BioNTech vaccines, which both deploy messenger RNA to teach the immune system to recognize and attack SARS-2 viruses. Novavax’s product uses tiny particles studded with viral proteins, mixed with an immune-boosting compound known as an adjuvant. The vaccine is composed of two shots, spaced three weeks apart, and the application is for use in adults aged 18 and older.

The firm noted that its more conventional development approach could make it appealing to people who are hesitant to be inoculated with the Pfizer or Moderna vaccines. 

“We believe our vaccine offers a differentiated option built on a well-understood protein-based vaccine platform that can be an alternative to the portfolio of available vaccines to help fight the COVID-19 pandemic,” Stanley Erck, Novavax’s president and CEO, said in a statement.

Novavax’s vaccine has demonstrated efficacy of about 90% against symptomatic disease in a large trial in the U.S. and Mexico, the biotech firm said, noting that its vaccines can generate an immune response against the omicron variant.

In the early months of the pandemic, Novavax’s vaccine was one of several selected for finding under Operation Warp Speed, the Trump administration’s effort to accelerate vaccine development. Yet ongoing manufacturing issues have slowed the company’s bid for regulatory approval. 

Novavax’s vaccine won its first authorization in November, in Indonesia, and it has since received authorization from other regulatory bodies, including the World Health Organization and the European Commission.