Despite large take-up rates in most OECD countries, millions of people still refuse COVID-19 vaccination. The large number of unvaccinated individuals raises major concerns about the diffusion of the virus. Anti-vax individuals are often very vocal about their choice and use social media to convince undecided individuals not to get vaccinated. Using original data from two surveys in nine OECD countries, we show that half of the individuals, who expressed anti-vax intentions in December 2020, were vaccinated by summer 2021. We find that information plays a key role. Vaccinations were more likely among individuals aged 50+, more informed on traditional media, trusting scientists, exposed to COVID-19, compliant with public restrictions, and less concerned about vaccines’ side effects. We also run a survey experiment with informational messages in the first wave. A striking result is that these informational treatments affected not only immediate vaccination intentions, but also actual vaccination rates recorded six months later – even among individuals, who had initially expressed anti-vax intentions. Altruistic messages, about protecting health or the economy, had the largest effect. Important differences in the relative impact of our different treatments across countries indicate that successful information campaigns should be tailored to the context.