Technically, you need a refresher but most dive centres do not offer these, they just run the course again.
In the US, a refresher course is comprised of the Skill Development and Exam sessions of the regular course. It is very common for instructors/shops to have refresher students simply join those sections of a full EFR course, which is even recommended in the EFR Instructor Manual. Accordingly, any shop that offers EFR essentially offers "a refresher course" too, even if they don't know it. Given that a refresher student doesn't need to attend the knowledge development or scenario portions of the course (or new materials) there's no reason to charge the same for a refresher as for the full course.
Do note that there are often differences in EFR/First Aid/CPR certification and refresher requirements between different countries, based on local regulations. Below is from the EFR Instructor Manual
in the US.
Emergency First Response Refresher Courses
Emergency First Response Refresher Courses are for people who have received training in CPR and/or first aid and want to refresh their training. Encourage your Emergency Responders to take refresher courses at least every 24 months.
Prerequisites - any previous CPR and/or first aid training (Emergency First Response or other).
Course Content - You can off er refresher training in Primary/Secondary Care together or separately.
Follow the Skill Development segment of the course(s) the participant needs refreshed. You can do this by having Refresher Course participants join the skill development portion of a regular class or you may conduct a stand alone refresher course. Be sure to also review any new developments or changes to primary care or secondary care techniques since participants last completed training. Keep in mind that this is an opportunity to teach or refresh skills on AED and Emergency Oxygen Use as well. Participants must take the exam for the course they are refreshing.
Materials Requirements: Reference required and recommended materials for the individual course you are teaching.
Recognition: When participants successfully complete an Emergency First Response Refresher Course, submit the appropriate Course Completion Authorization (Primary Care (CPR) and/or Secondary Care (First Aid) to your Emergency First Response Regional Headquarters. Participants will receive a new card(s) for the course they refreshed, showing that their skills for that course are current.