EVERETT — The flu season is in the rearview mirror.

For medical experts, it will be remembered for years to come for a couple of reasons.

“The 2018-2019 influenza season was the longest influenza season on record and was unusual in that there were two distinct peaks,” according to a summary memo from Dr. Yuan-Po Tu, who monitors influenza issues for The Everett Clinic.

The first peak was in late January was dominated by influenza A H1N1. The second peak was in April and was dominated by influenza A H3N2.

“Switching from one strain of influenza to another during a single season is not unusual,” Tu said. “However, usually the switch is from a strain of influenza A to B or influenza B to A and not a switch from one strain of influenza A to another strain of influenza A.”

Through April 20, there were 204 lab-confirmed influenza deaths statewide. Most occurred in people with underlying health conditions, or in the elderly. Two deaths have occurred in children. During the last three years, more than 200 statewide deaths a year have been attributed to the flu, including a high of 281 in 2017-18.

By comparison, there were just 14 during the 2011-12 flu season.

This year, Snohomish County has had 24 lab-confirmed flu deaths compared to 41 in Pierce and 32 in King counties.

The flu is a contagious respiratory illness caused by influenza viruses. The Centers for Disease Control estimates that between 3 percent and 11 percent of Americans catch the flu each year.

Those most vulnerable to serious complications are people 65 years and older; those with chronic medical conditions, such as asthma, diabetes, or heart disease; pregnant women, and children younger than 5.

Eric Stevick: 425-339-3446; stevick@heraldnet.com.