BRUSSELS, Dec 17 (Reuters) - European Commission is recommending vaccinated people receive booster doses no more than six months after their initial shots, with a further three month grace period for their COVID travel passes to be valid. Commission President Ursula von der Leyen said on Friday she had told EU leaders meeting for a summit in Brussels that the EU executive would present a delegated act on COVID passes. "We will ensure a common approach on boosters and the length of validity of the certificate. So boosters are recommended at the latest six months after full vaccination, and the certificate will remain valid for a grace period of three months beyond this."