Alert Yellow All the measures taken in Alert Yellow will continue where operationally feasible.   Inefficient human-to-human transmissions of flu caused by a novel virus, requiring close and sustained contact to an index case. Further spread can be prevented through public health measures to isolate cases and quarantine contacts. Risk of import into Singapore elevated. Isolated imported cases may occur but there is no sustained transmission. Strategy is to prevent further import of cases, and to ring fence and isolate cases to prevent spread. The focus will be to provide treatment of all cases, and antiviral prophylaxis to contacts including exposed healthcare workers. (Please also see below for the definition of other codes in the Alert System)
	Alert Green Isolated external or local cases of animal-to-human transmission. Threat of human-to-human infection remains low. The disease, if any, is basically limited to animals. Strategy is to step up vigilance and make preparations to meet the potential threat.
	Alert Orange Virus becoming increasingly better adapted to humans but may not yet be fully transmissible , requiring close contact with an index case. Larger clusters appear in one or two places outside Singapore but a pandemic has not yet been declared. A cluster of cases may also occur in Singapore but human-to-human spread remains localized. Public health measures such as isolation and quarantine will be effective to break the chain of transmission. Strategy is to contain spread arising from any local cases and break the chain of transmission, while preserving essential services and resources.
	Alert Red WHO declares that an influenza pandemic has begun. Singapore eventually also affected. Higher risk of acquiring the disease from the community once pandemic spreads to Singapore . Strategy is to mitigate the impact of the pandemic. All measures taken in Alert Orange will continue to be applied. Closing of school and suspension of selected events to prevent congregation of large groups of people.
	Alert Black High rates of severe disease and deaths. Emergency measures implemented to bring the situation under control. Healthcare and social support systems are overwhelmed by the pandemic. Economic activities are severely disrupted. Strategy is to ensure that medical & public health measures take precedence over social & economic considerations. Focus is to contain the “damage” and regain control of the situation, Drastic measures like stopping all social events may be implemented. The majority of measures are as in Alert Red plus the following action: Suspend all public gatherings, schools and Institutes of Higher Learning (IHL) closures. Issue advisory to public to stay home or even consider imposing curfew. For more information on the Disease Outbreak Response System, click here.