Flu vaccine had ‘moderate’ effectiveness during 2022-2023 season

Key takeaways:

• Vaccines reduced the risk of having a health care visit for influenza by 35% to 44%.
• This effectiveness held across subgroups, including older adults who are at increased risk for influenza complications.

Influenza vaccine efficacy during the 2022-2023 influenza season was “moderate” but still prevented many health care encounters and hospitalizations among adult patients, researchers determined.

“Influenza viruses are constantly changing, and it’s important to understand how well vaccines work each year,” Mark W. Tenforde, MD, PhD, medical officer in CDC’s Influenza Division, told Healio. “This helps to inform vaccine policy and to communicate the benefits of vaccination to health care professionals and the public.”

To provide an update on influenza vaccine effectiveness (VE) during the most recent influenza season, Tenforde and colleagues used a test-negative design to evaluate the vaccine’s performance in preventing influenza-A-associated ED and urgent care (UC) visits and hospitalizations among adults between October 2022 and March 2023. VE was estimated by comparing odds of seasonal influenza vaccination among patients with influenza A and those who tested negative.

In total, 85,389 ED/UC acute respiratory illness encounters — 17% of which were influenza A-positive, of whom 37.8% were vaccinated — and 19,751 hospitalizations — 9.5% of which were influenza A-positive, of whom 52.8% were vaccinated — were included in the study.

The study showed that VE against influenza-A-associated ED/UC encounters was 44% overall (95% CI, 40%-47%), whereas VE against influenza A-associated hospitalizations was 35% (95% CI, 27%-43%) overall.

When analyzed by age, VE was 45% among adults aged 18 to 64 years and 41% among those 65 years and older at preventing ED/UC encounters, and 23% and 41% at preventing hospitalizations among adults aged 18 to 64 years and 65 years and older, respectively.

Based on these findings, Tenforde said that vaccines successfully reduced the risk of having a health care visit for influenza and remained effective across subgroups, including individuals at an increased risk for influenza complications such as older adults.

“Millions of people in the U.S. get sick, and hundreds of thousands are hospitalized for influenza during a typical influenza season,” Tenforde said. “Even though they aren’t 100% effective, vaccines play a critical role in preventing illnesses and reducing the impact of influenza each year.”