Brussels/Amsterdam, 20 December 2021 (dpa/MIA) - The European Commission has granted the Covid-19 vaccine developed by US manufacturer Novavax conditional market authorization, President Ursula von der Leyen announced on Monday. "Vaccination, and boosters, are our best protection against Covid-19," the European Union's top official wrote in a tweet, praising the decision as widening the bloc's arsenal against the coronavirus. Novavax is the fifth vaccine approved for use in the EU, following a decision from the European Medicines Agency (EMA) in the wake of a special meeting on Monday in Amsterdam. The Maryland-based manufacturer applied for authorization in the EU in November. The EU's top medicines agency said the vaccine met the EMA's standards for effectiveness, safety and quality. The vaccine is designed to be taken in two doses, about three weeks apart, and has demonstrated an effectiveness against Covid-19 of about 90 per cent. It is not clear how powerful its protection is against the Omicron variant, which is currently spreading worldwide. In contrast to the four other shots already approved, Novavax is a protein-based vaccine. It contains tiny particles consisting of a laboratory-produced version of the spike protein of Sars-CoV-2, the virus that causes the Covid-19 disease. The Pfizer/BioNTech and Moderna preparations are messenger RNA vaccines while AstraZeneca and Johnson & Johnson's are vector-based. This difference may help convince some vaccine sceptics who do not wish to take the vaccines currently on offer in the EU. In August, the European Commission signed a contract with Novavax for delivery of 100 million doses of vaccine starting in the first quarter of 2022. The commission said in a press release that EU member states also have the option to purchase an additional 100 million doses during the course of 2022 and 2023.