EU leaders agreed last week to work on vaccine certificates, for which southern countries such as Spain and Greece are pushing to unlock tourism this summer.
However, a number of countries say it will first need to be established that vaccinated people cannot transmit the virus to others. Some countries, such as France and Belgium, also expressed concern that easing travel only for inoculated people would be unfair.
The Commission said it would seek to avoid discrimination against citizens who have not received a vaccine.
EU countries agreed in January on the basic data requirements of a vaccination certificate. A Commission spokesman said the EU executive would seek to coordinate on security standards and help connect the national health systems.