There are no mandatory vaccination requirements for Sri Lanka but Polio, Tetanus, Typhoid, Hepatitis A are recommended.
The risk of malaria is minute, so you may wish to consult your GP or travel health clinic for further medical advice.
Dengue fever is a risk in places visited. It is a tropical viral disease spread by daytime biting mosquitoes. Currently no vaccine available for Dengue, therefore the best type of prevention is to avoid being bitten. We recommend you take the usual precautions to avoid mosquito bites when in Sri Lanka.