**6. Discussion**

Methodological consistency is crucially important when monitoring the durability of new net types, due to there not being validated methods to assess these tools. Even small

differences in testing methods may lead to additional sources of variation in endpoints, making results difficult to interpret between countries, studies, and test facilities. The use of standardized testing methods streamlines the process of product evaluation, leads to a more rapid generation of consistent performance data across studies, and subsequently speeds up product uptake. In vector control, methods for new tools with novel modes of action are often developed in one site or by one group in response to a specific product or research question. This can narrow the applicability of that method, make it challenging to adopt it at other sites, or it may not be applicable to all products within a particular product class.

Developing evaluation methods in a collaborative group ('consensus' SOPs) allows the process to benefit from the collective knowledge and experience of a diverse set of stakeholders, and maximizes the chances for a specific methodology that will be widely relevant. However, developing a consensus SOP is just one of the first steps in the methodvalidation pipeline. Defining and improving the robustness of a method can be viewed as an incremental process which follows a stepwise progression from singular SOPs to consensus SOPs, to consensus SOPs that are experimentally validated at one site, and finally, to consensus SOPs that are validated at multiple sites. In this publication, we have defined the desired endpoints, and designed and refined methodologies for evaluating the biological durability of three new net types. The next steps in this process will be to (1) quantify inherent errors in the methods, (2) evaluate the ability of the methods to accurately characterize the vector control product, and (3) validate these results in multiple facilities. The scope of this would include assessing the methods' ability to measure the biological durability of different products within the class of nets, and against different vector species. More information is gathered when a method is in operational use, which can help to improve or refine the method. At this stage, it is imperative to ascertain that the methods can be implemented and used successfully within research teams, and identify training needs, if required. This is to ensure that data collected using these methods are as transferable and comparable as possible.

The agreemen<sup>t</sup> on key entomological endpoints to be measured, followed by the use of standardized and validated methods to measure them, needs to be partnered with an acceptance of the need for flexibility in product evaluation. For instance, the SOPs developed here have been formulated based on nets that are currently in development/on the market and therefore may be unsuitable for new formulations or designs within the same product classes. However, it should be noted that this is the way that previous ITN guidelines were developed—in response to new technologies coming to market [6]. It is challenging to 'future-proof' methods from the outset, especially in a rapidly evolving landscape which must be sensitive to the pressures of evolving and emerging insecticide resistance. Therefore, the process cannot be averse to change or updates in the future, which would lead to stagnation in innovation and delayed decision making—such has been the situation with non-pyrethroid products being evaluated with tests designed for pyrethroids. Regular updates of guidance based on consensus among key stakeholders will harmonize data collection procedures and, ultimately, hasten progress towards the goal of bringing new vector control products to market more rapidly, using robust data-driven decision making.

To take this further, the dissemination of up-to-date methods is crucial to ensure relevant data are being collected whenever possible. This process, convened under the auspices of the Innovation to Impact programme, sought to align methodologies used by those conducting durability monitoring activities of new net types (so-called 'nextgeneration ITNs'). While this objective was largely achieved through the engagemen<sup>t</sup> and insight of those involved, it is important to recognize that even though this process involved the key stakeholders in designing and implementing durability monitoring, the current durability monitoring guidelines [6] for these products may differ or simply do not exist. There is a clear need for further engagemen<sup>t</sup> with normative (WHO and control

programmes) and implementation groups (Roll Back Malaria and others) to ensure up-todate guidance for durability monitoring is available to all who may wish to access it.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/insects13010007/s1, Additional File 1: Developing consensus SOPs for evaluating new types of insecticide-treated nets—supplementary tables and figures; Additional File 2: I2I-SOP-001: Methods for monitoring the biological durability of insecticide-treated nets containing a pyrethroid plus piperonyl butoxide (PBO); Additional File 3: I2I-SOP-002: Methods for monitoring the biological durability of insecticide-treated nets containing a pyrethroid plus pyriproxyfen (PPF); Additional File 4: I2I-SOP-003: Methods for monitoring the biological durability of insecticide-treated nets containing a pyrethroid plus chlorfenapyr (CFP)s.

**Author Contributions:** Conceptualization, N.L. and R.S.L.; Formal analysis, N.L.; Funding acquisition, A.S. and R.S.L.; Investigation, N.L., J.S.A., K.G., S.R.I., J.L.M., L.A.M., S.J.M., C.N., R.O., A.S., R.S.L. and N.P.; Methodology, N.L., J.S.A., K.G., S.R.I., J.L.M., L.A.M., S.J.M., C.N., R.O., A.S., N.P. and R.S.L.; Project administration, N.L. and R.S.L.; Supervision, R.S.L.; Visualization, N.L.; Writing— original draft, N.L.; Writing—review and editing, N.L., J.S.A., K.G., S.R.I., J.L.M., L.A.M., S.J.M., C.N., R.O., A.S. and R.S.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Bill & Melinda Gates Foundation, gran<sup>t</sup> number INV-004350, through Innovation to Impact (I2I) at the Liverpool School of Tropical Medicine. Financial support for this study was provided by the US President's Malaria Initiative.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article or supplementary material.

**Acknowledgments:** The authors would like to thank C. Fornadel, L.A. Gerberg, J.E. Gimnig, S. Poyer, J. Wagman, M. Yoshimizu, and S. Zohdy for participating in stakeholder calls, L. Djogbenou for comments on the PPF-SOP, and S. Stutz and J. Austin for participating in a sub-group discussion for Interceptor G2.

**Conflicts of Interest:** The authors declare no conflict of interest. The findings and conclusions in this manuscript are those of the author(s) and do not necessarily represent the official position of the Centers for Disease Control and Prevention or the U.S. President's Malaria Initiative.
