Officials unsure why flu season was mild in Oklahoma

State health officials say the reasons for the decline from 872 hospitalizations and 26 deaths in 2011 to 316 hospitalizations and nine deaths in 2011 are difficult to pinpoint.

The flu season typically runs September to May, but started in January for unknown reasons, said Dr. Kristy Bradley, the state epidemiologist.

“That's just the fascinating aspect of influenza surveillance, no two seasons are ever exactly alike, and what the next year's season will look like is totally unpredictable,” Bradley said.

A possible explanation is that the three strains circulating this year, Type-A, Type-B and the H1N1 virus, have also appeared in Oklahoma since 2009.

“Many people already had immunity, either through immunization with the seasonal flu vaccine or from prior illness and recovery,” from those strains, Bradley said.

An increase in the number of people receiving flu shots, a statistic not specifically tracked by the department, appeared unlikely.

The department provided about 90,000 doses of flu vaccine to county health departments statewide for the 2012 season, down from about 155,000 last year, according to department spokeswoman Leslea Bennett-Webb.