Dec 20 (Reuters) - The European Union on Monday approved the use of Novavax"s (NVAX.O) COVID-19 vaccine in people 18 years and older, giving a boost to the U.S. biotech after long delays and paving the way for a fifth shot in the EU as the Omicron variant spreads. Data from two large studies showed the vaccine has an efficacy of around 90%, the European Medicines Agency (EMA) said. read more It is not clear yet how Novavax performs against the Omicron variant, or whether a booster dose will be needed. Some early data has suggested that many two-dose vaccines do not work well against the variant while a third shot improves their efficacy. Novavax said earlier this month it could begin manufacturing a vaccine tailored for Omicron in January. Novavax shares closed down more than 7% on Monday. Novavax said it would start shipping vaccines to the EU"s 27 member states in January as part of its deal to supply up to 200 million doses. Member states have ordered around 27 million doses for the first quarter, enough to inoculate about 13.5 million people, the Commission said. COVID-19 infections have broken records in parts of Europe in recent weeks, with governments and researchers scrambling to bolster defences against the fast-spreading Omicron, prompting renewed curbs ahead of the Christmas holidays. "May this authorisation offer a strong encouragement to everyone who has not yet been vaccinated or boosted, that now is the time to do so," said the head of the bloc"s executive Commission, Ursula von der Leyen, in a statement. The endorsement for the two-dose vaccine, branded Nuvaxovid, comes well ahead of possible authorisation in the United States, where Novavax has had to resolve manufacturing issues. Chief Executive Stanley Erck said he expects Novavax to file for U.S. authorization in the next week to 10 days. The regulatory process in the EU has taken longer than expected too. The EMA started a real-time rolling review of the data in February. read more Vials with a sticker reading, "COVID-19 / Coronavirus vaccine / Injection only" and a medical syringe are seen in front of a displayed Novavax logo in this illustration taken October 31, 2020. REUTERS/Dado Ruvic Vials with a sticker reading, "COVID-19 / Coronavirus vaccine / Injection only" and a medical syringe are seen in front of a displayed Novavax logo in this illustration taken October 31, 2020. REUTERS/Dado Ruvic The shot received its first regulatory green light in Indonesia last month and is awaiting approval in Japan, where it would be manufactured and distributed by Takeda Pharmaceutical (4502.T). Erck said Novavax has already delivered millions of shots to Indonesia, which has begun administering doses. On Friday, the World Health Organization (WHO) issued an emergency use listing to Novavax"s vaccine made by the Serum Institute of India (SII), the world"s biggest vaccine maker, paving the way for its use in low- and middle-income countries where rollout has been much slower than in Europe. Novavax said on Monday it had received the WHO"s emergency use listing for the company"s own version of the vaccine, which it will distribute in Europe and other markets. Erck said Novavax is awaiting guidance from COVAX on initial order volumes and expects to begin most deliveries in the first quarter of 2021. DIVERSIFICATION Vaccines from Pfizer-BioNTech (PFE.N), (22UAy.DE), Moderna (MRNA.O), AstraZeneca (AZN.L) and J&J (JNJ.N) have already been approved for use in the EU. Novavax"s protein-based vaccine uses alternative technology to the other four shots, which helps the EU diversify its portfolio of vaccines. Still, it will be deployed into a market dominated by the Pfizer-BioNTech shot. The U.S.-German partners have contracts for the supply of up to 2.4 billion doses through 2023 for the EU"s population of 450 million. Almost 70% of EU citizens have received two vaccine doses and many countries are scrambling to administer third booster doses in a bid to strengthen defences against Omicron. With concerns about rare blood clotting, many EU countries have reduced their use of the AstraZeneca and J&J shots and many have donated them to low-income countries directly or through the COVAX programme run by the WHO. Novavax has about eight manufacturing locations, including those of the SII. Production of the shot in India at SII has also been approved by the EMA, an EU official told Reuters. Antigens for the vaccine, the inactivated organisms that trigger an immune response, are made at Novavax"s factory in the Czech Republic.