1st to January 31st and aggregated them at the individual level, across different waves. The final experience sample contains information from 5,205 individuals, equally split between treatment and control districts.

The cross-sectional sample measured the accumulated and medium-terms impact of the campaign on malaria incidence, risk perceptions, and bed net-related actions and intentions. Some questions from the longitudinal survey were reiterated, with variations in the time periods for respondents to report on. For example, while the experience surveys inquired whether participants or their family members had experienced malaria in the past two weeks, the cross-sectional survey posed a similar question but with reference to the last 6-8 months, i.e. since August 2020, when the study campaign went live. We also asked about malaria risk perceptions, and intentions to buy or treat bed nets with insecticide. The cross-sectional sample comprises 3,052 observations. As discussed in Section 6, in the cross-sectional study we also nested an individual-level study to explore the mechanisms behind the lack of program impacts on households living in non-solid dwellings.

For both samples, recruitment was stratified across districts and dwelling type, as described previously. The enrollment questionnaire started asking participants about their preferred language (English, Hindi, or Odia), followed by providing study details to obtain individuals’ informed consent for their participation in the research. Only individuals aged 18 or above and whose consent was obtained are part of our survey samples. Prior to analysis, we standardized and refined the samples to enhance data integrity. Specifically, we removed respondents who hastily completed the survey<sup>24</sup> and those reporting to be above 90 years old and indicating a household size exceeding 30 members, retaining only observations where all outcome and control variables were present.

We complemented survey data with administrative health facility data collected at the subdistrict-month level from the Indian Health Management Information System (HMIS).<sup>25</sup> This dataset provides monthly information from health facilities at the sub-district level, detailing the number of malaria tests performed and the positive cases identified. It separates the data for urban and rural health facilities, which is used for analyzing treatment effects specific to each setting. The dataset spans from April 2020 to May 2021.<sup>26</sup> We designated April to August 2020 as the pre-treatment period and September 2020 onwards as the treatment period, aligning with the dissemination of the campaign in the study states. The use of administrative records complements and expands upon the analysis of survey data in two important aspects. (1) The use of objective malaria indicators alleviates the concern that our results could be driven by social desirability bias and experimenter demand effect, as these might be present in survey responses but not in health facility records. (2)

> 24By employing time data collected for each survey question by Virtual Lab, we omitted observations where the 90th percentile of response time was less than 3 times the fastest response time. This procedure accommodates variations in respondents’ capabilities and response velocities.

> 25HMIS is a monitoring system that has been put in place by the Indian Ministry of Health & Family Welfare (MoHFW). It collects facility-wise monthly information on a variety of health outcomes, and processes and reports the information at Sub-district, District, State and National levels. The records in this dataset are considered to meet the required standards for completeness for health research in India (Sharma et al., 2016).

> 26Although data from previous periods is available, the total number of sub-districts per state and their boundaries were different and matching across years was imprecise. Hence, we excluded previous observations and focused on an homogeneous set.

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