We summarise the empirical evidence on effects of asset purchases in the euro area, including the PEPP programme launched in response to the COVID-19 crisis. We conclude that QE is particularly effective during times of high financial stress, i.e. at the peak of a crisis, but tends to lose impact over time. At the same time, QE policies come with prominent risks which may materialise only in the longer term. We suggest a scheme of rule-based intervention in sovereign debt markets that preserves the role of yield spreads as a market signal, while containing the risk of bad equilibria.