To determine whether an association exists between daily weather variables and headache days during non-treatment periods, and if so, whether fremanezumab use modifies this association.

To date, the effects of preventive migraine treatments on weather-triggered headaches have not been investigated.

HALO-EM was a 28-week, Phase 3, double-blind, placebo-controlled study assessing the efficacy of fremanezumab in adults with episodic migraine (EM). This post-hoc analysis compared daily headache diary data from participants enrolled in the United States (US) with daily, region-specific weather variables (barometric pressure, dry bulb temperature, relative humidity, precipitation, and wind speed) from the National Climactic Data Center. Primary outcome measures: any-onset headache (AOH) days (any day with a headache) and new-onset headache (NOH) days (headache on a given day with no headache the preceding day). A generalized, linear, mixed model was used to explore the association between weather variables and AOH and NOH days among participants during non-fremanezumab and fremanezumab treatment periods. These associations were then compared between treatment periods.

Of the 676 US participants reporting 76,084 daily diary records, 660 were included in the final analysis (71,030 days of data). Most participants were female (85.2%); mean age was 41.2 years; and 19.4% had concomitant preventive treatment use. Mean number of headache days at baseline were 11.2, reducing to 7.8 and 6.7 days for placebo and fremanezumab, respectively. Every average daily temperature increase of 10^?F significantly increased the risk of having an AOH day (odds ratio [OR]: 1.06, p<0.0001) or NOH day (OR: 1.06, p=0.0003). Throughout 3 months of fremanezumab treatment, ORs for an AOH or NOH day reduced to 1.02 and 1.01, respectively, and were no longer statistically significant.

Fremanezumab treatment attenuated the association between weather variables and AOH or NOH days, suggesting that fremanezumab may prevent weather-triggered headaches in people with EM.