Remark:

• In areas approaching elimination or post-elimination settings where proactive indoor residual spraying (IRS) is occurring, programmes can consider switching to reactive IRS only, depending on the receptivity of the area.
• Programmes considering adding reactive IRS on top of proactive IRS should balance the potential added benefit with increasing cost and the risk of insecticide resistance.
• In areas approaching elimination or post-elimination settings where no IRS is occurring, initiating reactive IRS may be beneficial, depending on whether IRS is a suitable vector control strategy. IRS is most effective where the vector population is susceptible to the insecticide(s) being applied, the majority of mosquitoes feed and rest indoors and where most structures are suitable for spraying.
• If the index infection was imported and the residence is not located in a receptive area, there may be no benefit from reactive IRS.

Practical info Please refer to the Practical Info section for IRS (4.1.1) for more information on operational issues related to IRS. When used, reactive IRS should be one among several components of a programme to eliminate or prevent reestablishment of malaria, including intensive surveillance as described in the Framework for malaria elimination [9]. Reactive IRS depends on a strong passive surveillance system that detects suspected cases, tests all suspected cases for malaria with a parasitological test and investigates all cases at their place of residence. If these elements are not in place, it is unlikely that an reactive IRS intervention can be effectively implemented. It is essential to determine the likely location of infection through a case investigation that identifies the location of the person during the likely period of infection in order to understand where the reactive IRS intervention should take place. Reactive IRS should be applied to the residence if the person is determined to have been infected locally. Programmes should extend RIRS to neighbours, with the radius of implementation depending on the local epidemiology and ecology of malaria. If the index infection is not likely to have been acquired at the residence, reactive IRS might still reduce the chances of onward transmission. However, if the infection was classified as imported and the household is not located in a receptive area, there may be no benefit to reactive IRS. In very low to low transmission settings where standard IRS is occurring (proactive spraying), there may be advantages to programmes from switching to reactive IRS. Decisions to switch from standard IRS to reactive IRS should be based on assessments that include:

• the potential risk of increasing malaria transmission by scaling back proactive IRS;
• the potential cost savings;
• the potential for increased acceptance and equity; and
• the potential for reducing insecticide resistance. In settings where no standard IRS is occurring, reactive IRS may be beneficial, depending on the factors listed below.
• The programme has the capacity to conduct case investigations at the residences of cases to determine whether the case is imported or local.
• The capacity of the vector control programme to respond quickly to conduct reactive IRS after identification of a confirmed case.
• The population living in the houses where RIRS is applied are at risk of infection.
• The majority of the vector population feeds and rests indoors.
• The vectors are susceptible to the insecticide that is being deployed.
• People mainly sleep indoors at night.
• The majority of structures are suitable for spraying. Programmes considering adding reactive IRS on top of proactive IRS should balance the potential added benefit with the risk of insecticide resistance and increased cost, and develop protocols that take into account the time since the dwelling was last sprayed. Reactive IRS depends upon a strong passive surveillance system that detects suspected cases, tests all suspected cases for malaria with a parasitological test and investigates all cases at the residence. If these elements are not in place, it is unlikely that an reactive IRS intervention will have an impact on malaria transmission.