- Acute disease at the time of enrolment. Acute disease is defined as the presence of a moderate or severe illness with or without fever. Enrolment will be deferred until condition is resolved. All vaccines can be administered to persons with a minor illness such as diarrhoea, mild upper respiratory infection with or without low-grade febrile illness, i.e. oral/ axillary temperature < 37.5 °C (99.5 °F).