Conceptual illustration of the iceberg effect regarding the COVID-19 pandemic. The iceberg effect likens patients diagnosed with a disease during an outbreak to the tip of an iceberg. In the case of some diseases, many more people may be infected than is apparent. Reasons for this can include a long incubation period and patients showing no symptoms or symptoms which are difficult to detect. The iceberg effect is especially significant where the long-term affects of a disease are not fully understood, as is the case with COVID-19.