With the omicron wave of the pandemic rapidly spreading across the U.S., the robust economic recovery is facing a new threat that policymakers have little control over: people calling in sick.

What started as a series of holiday flight cancellations as pilots and other staff fell ill or were forced into quarantine is becoming a reality in factories, grocery stores and ports and again testing supply chains.

The widespread sick absences are already constraining output, and several economists began the new year by downgrading their first-quarter forecasts. Even if the hit is temporary, as most anticipate, the disruptions and closures are likely to slow the fragile rebound in some sectors and weigh on businesses’ future plans.