Indirect effects of doxyPEP implementation reveal core-group dynamics of bacterial sexually-transmitted infections

DoxyPEP uptake by 9% of at-risk men who have sex with men (MSM) and transgender women (TGW) is linked to strong indirect protection against bacterial STIs within their sexual networks.

• Why it matters: Core-group theory predicts that high-risk individuals disproportionately sustain transmission, but the operational scale across sexual networks is unclear for bacterial STIs.
• What they did: Using doxycycline post-exposure prophylaxis (doxyPEP) implementation as a natural experiment, the study estimated changes in chlamydia and syphilis risk among doxyPEP recipients and non-recipients within MSM and TGW networks.
• The result: Chlamydia and syphilis declined by 80% (95% CI: 71–86%) and 65% (30–82%) among recipients, and by 41% (32–48%) and 29% (13–42%) among non-recipients, with no incidence impact among females and other males.

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