For up to date information you need the foreign office website.
"All visitors to Costa Rica arriving from any of the following countries (Colombia, Brazil, Venezuela, Peru, Ecuador, Bolivia, French Guyana, Angola, Democratic Republic of the Congo, Gabon, Cameroon, Nigeria, Benin, Ghana, Burkina Faso, Liberia, Sierra Leone, Guinea, Gambia and Sudan) are now required to produce an International Certificate of Vaccination or Prophylaxis documenting yellow fever vaccination before entry to Costa Rica will be granted. Certificates are valid 10 days after the date of vaccination."
Surely better safe than sorry?
Thank you very much for this answer, my jab is booked, also it was interesting to see from website www.nathnac.org that it seems a Yellow Fever Cerificate will be required to be produced when returning to Barbados. Thanks again very helpful.