Brussels, Jan 12 : Citing preliminary data, the European Medicines Agency (EMA) has said that the Covid-19 vaccines remain effective against severe disease and hospitalisation caused by the Omicron coronavirus variant. "Although Omicron appears to be more infectious than other variants, studies conducted in South Africa, the UK and some European Union (EU) member states show a lower risk of being hospitalised after infection with Omicron. Based on these studies, the risk is currently estimated to be between a third and half of the risk with the Delta variant," the EMA said on Tuesday in a release. It cited results from recently published studies as showing that vaccine effectiveness against symptomatic disease is lower for Omicron than for other variants and tends to wane over time. As a result, more vaccinated people are likely to develop breakthrough disease due to Omicron. However, these studies also show that vaccination continues to provide a high level of protection against severe disease and hospitalisation linked to the Omicron variant, Xinhua news agency reported. The latest evidence, which includes real-world effectiveness data, also suggests that people who have had a booster dose are better protected than those who have only received their primary course. The EMA's Head of Vaccines Strategy, Marco Cavaleri, said at a press conference on Tuesday that the agency continued to monitor the vaccines' effectiveness, and the outcome of this assessment may impact future vaccination strategies recommended by experts in the EU member states. He added that having to take a booster dose every three or four months was not effective enough as a long-term strategy. "We do not yet have data on the fourth dose to allow us to express ourselves, but we are concerned about a strategy that foresees going ahead with vaccinations in a short time," he said. The EMA added in the statement that efforts should continue to increase full vaccination uptake in individuals who are currently unvaccinated or partially vaccinated and to accelerate the rollout of booster doses. /IANS