Influenza vaccinations helped to reduce severe illness and death by 32% in the 2019-2020 flu season, according to a new study that included hospitalized patients.
Vaccine effectiveness against worst-case health outcomes is not well understood, said the authors. Their study aimed to gauge the ability of flu vaccines to prevent influenza-associated severe acute respiratory infection. To do so, they compared a control group with a cohort of confirmed flu patients treated at 10 hospitals, including in intensive care.
Among 638 study participants, 45% percent of those diagnosed with influenza were vaccinated, as were 61% of the control group. The season’s flu vaccine was 28% effective against influenza A and 52% against influenza B, they reported. Estimates were adjusted for age, comorbidities and other confounders.
Older adults who received the flu vaccine that season were notably less protected than their younger cohort against acute respiratory symptoms. Vaccination also was more protective against influenza-associated death than it was against nonfatal illness, the researchers found.
Efficacy slid downward among patients aged 50 to 64 years and again in patients aged 65 years and older, added corresponding author Wesley H. Self, M.D., MPH, of Vanderbilt University Medical Center, and colleagues.
Vaccine effectiveness can be influenced by several factors, including characteristics such as age and health, as well as the match between the flu viruses currently in circulation and the flu vaccine in use.
Many studies since 2010 have found that flu vaccines reduce the risk of hospitalization among adults aged 65 or more years by 54% against A(H1N1) viruses, and by 31% against influenza B viruses on average, according to the CDC. But protection against influenza A(H3N2) flu viruses is less consistent, the agency noted.
The study was conducted by a team with the Influenza Vaccine Effectiveness in the Critically Ill (IVY) Network, a collaboration of academic medical centers in the United States that studies influenza and COVID-19.
