f-both-interventions-are-implemented-and-affect-independent-portions-of-exposure

Question

Baseline secondary attack rate in a household for a novel respiratory virus is estimated at 20%. Two independent interventions are available: Intervention A (source masking) reduces transmission probability per contact by 40%; Intervention B (hand hygiene + surface disinfection) reduces fomite-mediated transmission by 50%. Assuming these reductions apply independently to distinct fractions of transmission and that the combined effect on overall per-contact transmission probability can be approximated by multiplicative reduction, what is the new overall secondary attack rate if both interventions are implemented and affect independent portions of exposure?

Accepted Answer

Approximately 6% (a reduction from 20% to ~6% when the independent effects are combined multiplicatively).

Answer

Approximately 10% because you average the two percent reductions (40% and 50%) to get 45% reduction and then apply it to 20% yielding 11%, rounded to 10% as a simple field estimate for planning purposes rather than precise calculation.

Answer

No change (20%) because interventions targeting source masking and fomite control are redundant and cancel each other out in real-world settings, making any mathematical combination irrelevant for policy decisions.

Answer

Approximately 12% because you subtract 40% then 50% sequentially from 20% (20% − 40% = negative so assume floor at 0%), and therefore the realistic remaining attack rate is around 12% after adjusting for implementation loss, which is a conservative practical estimate a policy maker might choose.