"There have been a number of variants over the last months and we expect more," said Marco Cavaleri, European Medicines Agency's (EMA) head of vaccine strategy, during a press briefing.
"It's very important that there is continuous monitoring and a close surveillance of the performance of all the approved vaccines against emerging variants."
The highly transmissible Delta variant of SARS-CoV-2 was first identified in India and has led to a wave of new infections around the world.
To monitor potential new threats, vaccine makers have exposed the blood of vaccinated people to viruses engineered to have the typical features of the variant of concern to determine if neutralizing antibodies quell that virus.
Currently, the European Union has four COVID-19 vaccines authorized: those from Pfizer and BioNTech, AstraZeneca
The EMA said it would proceed with evaluating data from CureVac's coronavirus vaccine after the German biotech firm said late on Wednesday its jab was only 48% effective in a final analysis.
The agency also reiterated that it had not received any application for authorization of Covishield, the version of AstraZeneca's vaccine made by India's Serum Institute, adding that it could approve or accept for use only those shots with ongoing applications.
Friction emerged between India and Europe in recent days over the exclusion of Covishield by the European Union vaccine passport programme as one of its accepted vaccines.