BRUSSELS (Reuters) - Britain needs to show a willingness to ship vaccines to the European Union, which is considering making reciprocity a condition of its vaccine exports in future, the head of the European Commission said on Wednesday. Ursula von der Leyen said it was hard to explain to EU citizens why vaccines were going to other countries, while hardly anything was heading the other way. “With the U.S. the reciprocity is given... There is a seamless flow back and forth of pre-products and raw materials and drug substance,” she told a news conference. However, she said that, while 10 million doses had gone form EU plants to Britain, the EU was still waiting for AstraZeneca vaccine doses from UK plants. “We are still waiting for doses to come from the UK, so this is an invitation to show us that there are also doses from the UK coming to the European Union so that we have reciprocity,” she said.