Influenza Vaccine Least Effective for Children Facing Secondary Infection
Researchers addressed vaccine effectiveness for individuals with direct household contacts that reported influenza.
For individuals who have had a direct contact with influenza living in their household, children were most likely to experience a secondary infection, despite overall vaccine effectiveness (VE) being modest across all demographics. While findings present new strategies to addressing influenza in the household, researchers still suggested that seasonal influenza vaccination is the best way to keep individuals and their household contacts protected from infection.
“Households, where individuals often interact in close contact, provide a favorable environment for transmission of respiratory viruses. Previous household studies indicated that 3% to 38% of household members would be infected after a first member was infected with influenza and identified school-aged children as important contributors to influenza transmission in households,” wrote authors of a study published in JAMA Network Open.1
An average of nearly 35 million individuals were infected by influenza annually from 2017 to 2020. | image credit: Nina Lawrenson/peopleimages.com / stock.adobe.com
With previous research regarding household influenza lacking for the past 10 or more years, researchers attempted to update their findings by addressing data from 3 consecutive flu seasons spanning from 2017 to 2020.
Before exploring the impacts of household influenza, or secondary influenza infection as researchers explained, it is important to first note the broader statistics for the flu seasons explored in the study. According to CDC data, influenza hospitalizations reached approximately 710,000 from 2017 to 2018, which was the highest since before 2010. Furthermore, an average of nearly 35 million individuals were infected annually from 2017 to 2020.2
While not unprecedented, recent influenza rates have been gradually increasing since before 2017. Combined with decreasing vaccination rates amongst the population, these recent trends have caused concerns for public health and infectious disease experts.
READ MORE: Why Vaccination Uptake is Crucial During the Winter Season
“While flu vaccination coverage among adults ≥65 years is high (69.7%) and approaching the Healthy People 2030 goal of 70%, coverage among adults <65 years has been steadily decreasing. Data from another CDC survey showed that younger adults were more likely to have at least one issue or concern with flu vaccination than adults ≥65 years, with the most commonly reported issue being that they are not worried about getting the flu,” according to authors of a CDC study.3
Focusing on patient outcomes for families living in close contact with influenza, researchers wanted to get a further grasp on how the virus spreads in a specific setting as well as the VE of influenza immunization in the household.
“During 3 consecutive influenza seasons (2017-2020), primary cases (the first household members with laboratory-confirmed influenza) and their household contacts in Tennessee and Wisconsin were enrolled into a prospective case-ascertained household transmission cohort study,” wrote the authors.1
Researchers included a total of 699 primary cases of influenza (median age, 13 years; 54.5% women; 79.1% White) and 1581 individuals (median age, 31 years; 52.7% women; 81.2% White) whose direct household contacts reported infection. Regarding both groups’ vaccination status, 49.1% of primary cases showed influenza vaccination and 50.1% of household contacts reported vaccination.
After discovering a total of 356 (22%) confirmed influenza infections among household contacts, researchers identified that this specific group was at an 18.8% risk of secondary infection. “The secondary infection risk varied with age and was highest among children aged less than 5 years (20.3%),” they continued.1
Furthermore, researchers determined VE was 21% for household contacts. However, they were sure to note that VE varied significantly by flu type and season.
From addressing influenza outcomes when observed in close living spaces to VE among various age groups in a specific population, researchers’ findings presented new ideas on how to address influenza outbreaks during the annual winter season. While promoting influenza immunization remains the most common effort for protecting the population against the virus, these findings have provided new pathways for experts to better understand the characteristics of influenza.
“Our study showed that following introduction of influenza virus infections in households, there is a high risk of transmission to household members. Children were commonly identified as primary cases, and contact household children experienced the highest risk of secondary infection…Although complementary preventive strategies to prevent influenza in household settings may be considered, seasonal influenza vaccination is the primary strategy recommended for prevention of influenza illness and its complications,” concluded the authors.1
READ MORE: Immunization Resource Center
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