Vaccination for Hepatitis A & B is recommended but not mandatory. Tuberculosis still occurs in Korea and it is advisable to have a regular skin test during your time living there. A yearly flu vaccine is recommended, particularly for those with asthma and other respiratory problems, who may be particular vulnerable due to the high levels of pollution.
Before coming to Korea you may consider boosting your immune system with a course of vitamin/mineral supplements.
Since 1989 all foreign residents wanting to stay in South Korea without their spouses for 91 days or more are required to undergo an HIV test. ESL teachers (on an E2 Visa) and Foreign Workers must also be tested. The number of people infected with HIV or AIDS is very low in Korea and the common perception that foreigners are the carriers is still prevalent. Those diagnosed when applying to come to Korea will generally be refused admittance.