Unusual early start to flu season prompts earlier vaccination timing

This year's influenza season is unfolding differently than in recent years, both in its timing and in where it first took hold, according to health reporting on the season's early trajectory.

Rather than emerging first in the South, as has been typical in recent flu seasons, this year's outbreak began in the West. The season also started earlier than usual, giving public health officials and clinicians less of the lead time they typically rely on to prepare vaccination campaigns.

A new variant may be playing a role

Part of the explanation may lie in the virus itself. A new flu variant carrying a mutation that helps it evade existing immunity appears to be circulating this season, and may be contributing to both the early onset and the shift in where the season began. Because the variant can partially sidestep immunity built up from prior infection or vaccination, it may be spreading more readily through populations that would otherwise have some protection.

The early and geographically unusual start to the season has implications for vaccination timing. Flu vaccines typically take about two weeks to produce full protection, and vaccination campaigns are usually timed to build population immunity before a season peaks. An earlier-than-usual season raises the prospect that people who wait until their typical vaccination window may find themselves exposed before they are fully protected.

Health officials continue to monitor the season's progression, including how the new variant's spread compares with past years and whether current vaccines remain well matched to circulating strains.