Russian and Chinese media are trying to sow mistrust in western COVID-19 vaccines, according to a European report.
The report says that between December and April, the two countries' state media outlets published fake news online in a number of languages.
They sensationalised vaccine safety concerns, publicised unfounded links between vaccines and deaths in Europe, and promoted their own vaccines as superior.
Both countries deny the allegations.
Russia's vaccine Sputnik V responded to the report by saying that it was the victim of disinformation, adding: "We will continue to fight disinformation campaign against Sputnik V in the interests of protecting lives around the world and avoiding vaccine monopoly that some vaccine producers may strive for."
China says its vaccines are a "global public good" and presents them as "more suitable for developing countries and also the western Balkans", according to the report.
Written by the EU's disinformation unit, the report said Russian and Chinese vaccine diplomacy "follows a zero-sum game logic and is combined with disinformation and manipulation efforts to undermine trust in Western-made vaccines".
"Both Russia and China are using state-controlled media, networks of proxy media outlets and social media, including official diplomatic social media accounts, to achieve these goals."
The report added: "Both Chinese official channels and pro-Kremlin media have amplified content on alleged side-effects of the Western vaccines, misrepresenting and sensationalising international media reports and associating deaths to the Pfizer/BioNTech vaccine in Norway, Spain and elsewhere."
The European Union began its own vaccination programme very slowly but it is now picking up pace.
The UK, which is no longer part of the bloc, has delivered at least one vaccine dose to more than 50% of adults.
According to the EU report, Russian media had said: "Brexit saved the UK from the 'vaccine chaos' engulfing the EU.
The report added: "Such narratives indicate an effort to sow division within the EU."