The European Union's drug regulator said Tuesday it has begun an accelerated review process for an experimental coronavirus vaccine booster made by the Spanish company Hipra.

The European Medicines Agency said in a statement that its evaluation is based on preliminary data from laboratory studies and research in adults that compared Hipra's booster shot to the vaccine made by Pfizer-BioNTech. It said early results suggest the immune response achieved with Hipra “may be effective” against COVID-19, including the hugely infectious omicron variant.

Hipra is a protein-based vaccine and is made using similar technology as the Novavax COVID-19 vaccine, which was authorized by the EMA and other agencies in December. It contains two versions of the coronavirus' spike protein that were made in a lab, which are intended to prompt an immune response when a person is immunized.

Hipra is intended to be a booster shot in people who have been fully vaccinated with a messenger RNA vaccine or a vector-based vaccine, like the ones made by AstraZeneca and Johnson & Johnson. Until now, Hipra has mainly focused on making vaccines for animals.

Scientists believe using different types of vaccines can increase the body's immune response and numerous countries have adopted a “mix-and-match” strategy for COVID-19 vaccination.

Hipra has reportedly sold tens of millions of its vaccine to Vietnam and has estimated it could make about 600 million doses this year.

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