Hey,
No I didn't take any second year courses, my last year was a mix of 3rd and 4th year. Do you know if the certificate will appear on your transcript? I think that you may be OK considering that you also have a CV and a Letter of Purpose to talk a bit about your certificate. I would definitely list it under Education with the year that your started and finished it and then maybe give an example of a few courses that relate to public health, and then in your Letter I'd just write a little bit about how you certificate "gives you an advantage"/ how it can be applied to the program. Personally I'd give you extra bonus points for doing it at the same time!
I know for most graduate programs they want to see the highest grades in courses that relate to that graduate degree, but as long as you meet the minimum average they won't reject you right away.