Flu Shots Help Stop Spreading Influenza at Home

With Thanksgiving gatherings planned for late this week, a new study suggests that everyone should get their annual flu shots.

A recent study concluded that the risk of secondary influenza among unvaccinated household contacts is approximately 15% to 20% after a person infected with the influenza virus introduces it into households.

This prospective case-ascertained household transmission study was conducted at two sites during three consecutive influenza seasons with daily data collection and respiratory specimens following the introduction of infections in the households; researchers observed a substantial risk of subsequent influenza virus infection among household contacts.

According to this JAMA Network Original Investigation, published on November 21, 2024, the secondary infection risk of influenza infection among household contacts was 18.8% (95% confidence interval, 15.9% to 22.0%).

And the estimated vaccine effectiveness (VE) of flu shots for preventing secondary infections among household contacts was 21% (95% CI, 1.4% to 36.7%).

The estimates of VE against any influenza virus infection in the present study were lower than those generated from surveillance of medically attended illness.

The U.S. CDC influenza VE network estimated that vaccines' overall effectiveness in preventing medically attended influenza was 38%, 29%, and 39% in 2017 to 2018, 2018 to 2019, and 2019 to 2020 flu seasons, respectively.

This study's observations of relatively modest VE against infection could suggest that vaccines confer different degrees of protection against infection than more severe outcomes or that VE is lower in close contact environments like households.

Vaccines can confer higher protection against severe outcomes like hospitalization than against outpatient visits. They may confer better protection against severe outcomes during years of close antigenic match between the circulating virus and the vaccine strain.

As of late November 2024, various flu shots have been approved for this year's flu season.

From an availability perspective, the CDC reported over 92 million flu shots had been distributed in the U.S., targeting the 2024-2025 flu season. These vaccines are generally available at health clinics and pharmacies throughout the U.S.