Influenza Vaccine Effectiveness Among Pediatric Patients
In this podcast, Nicole Hood, MPH, discusses the results of her team's study examining vaccine effectiveness among pediatric patients across nine influenza seasons from 2011 to 2020.
Additional Resource:
- Hood M, Flannery B, Gaglani M, et al. Influenza vaccine effectiveness among children: 2011-2020. Pediatrics. 2023;151(4):2022059922. doi:10.1542/peds.2022-059922.
Nicole Hood, MPH, is an Oak Ridge Institute for Science and Education (ORISE) fellow in the influenza division at the CDC.
TRANSCRIPT:
Leigh Precopio: Hello everyone and welcome to another installment of Podcasts360, your go-to resource for medical education and clinical updates. I'm your moderator, Leigh Precopio, with Consultant360 a multidisciplinary medical information network.
Vaccination is one of the first line preventative measures against influenza and its associated adverse effects in pediatric populations who are at an increased risk of severe disease. However, many factors influence vaccine effectiveness in infants and children, including the patient's age, the influenza season, and the virus type or subtype. To better understand the effectiveness of inactivated influenza vaccine, the authors of a recent study examined the rates of outpatient influenza illness in pediatric patients across nine influenza seasons following the 2009 H1N1 pandemic.
Joining us today to discuss the study implications is lead study author Nicole Hood, who's an ORISE fellow in the influenza division at the CDC. To begin, could you discuss what knowledge gaps your team was hoping to bridge with this study?
Nicole Hood, MPH: So in this study, we hoped to bring some insight into vaccine effectiveness (or VE) of the flu vaccine in children over a nine year period from the 2011 influenza season to the 2020 influenza season, which were the seasons immediately following the 2009 influenza A H1N1 pandemic and prior to the COVID 19 pandemic, respectively. Unlike vaccine efficacy studies which provide the initial information as to whether the vaccines are safe and effective under optimal conditions, VE studies enable us to better understand how the vaccine performs in more diverse settings and groups of people, which is what this study sought to do.
So each year we at the CDC, as well as other research groups, conduct studies on vaccine effectiveness of that particular season's influenza vaccine. However, there are very few studies that pool vaccine data across multiple years to better understand patterns.
Such an understanding is especially important because of the variability of each flu season's ability to protect against the relevant circulating influenza viruses for the given season. So additionally, VE can vary by age and influenza virus type and subtype. So we wanted to provide some greater insight into long-term variation by these characteristics as well. Because we've been collecting and reporting such data for several years, we are uniquely positioned to analyze patterns of VE, both in terms of overall VE and VE against certain influenza types and subtypes, which for this study included influenza A H1N1, influenza A H3N2, and influenza B.
Leigh Precopio: The results of your study found that 39% of overall participants were vaccinated for influenza and they pulled vaccine effectiveness for all influenza seasons was 46%. Are these results that surprised you? Why or why not?
Nicole Hood: So our findings in pediatric groups are consistent with previous studies in older ages showing differences in VE by virus type and virus subtype. So for example, a meta-analysis reporting pooled VE of influenza A subtypes H3N2, and H1N1, and influenza type influenza B found that VE was higher against influenza A H1N1 and influenza B compared with influenza A H3N2. Similarly, in our analysis among pediatric age groups, VE for influenza A H1N1 and VE for influenza B were similar to each other and higher than VE for influenza A H3N2.
Leigh Precopio: How does understanding vaccine effectiveness inform both future vaccination efforts and other influenza related preventative measures?
Nicole Hood: Further information on the effectiveness of influenza vaccination in pediatric age groups can really help communicate the benefit of vaccination to both parents and caregivers. It can help us better focus our messaging on the importance of vaccination to people who may benefit the most and/or may be most vulnerable to influenza. It can also help us better target non-vaccine related preventative measures to age groups who don't experience the same levels of protection from the vaccine that other age groups do.
Leigh Precopio: What knowledge gaps remain about influenza vaccine effectiveness in pediatric patients and what are the next steps for research?
Nicole Hood: Yeah, so overall, and by type and subtype of influenza, we found that VE against influenza illness was highest among children in the 6- to 59-month age group compared with older pediatric age groups. And VE was lowest for influenza A H3N2 virus infection. Therefore, understanding reasons for the higher VE estimates in the youngest age group of children might inform efforts to design improved influenza vaccines.
Furthermore, there still isn't much known about how children's past experiences and infections with influenza virus may affect their protection against future infections and the effectiveness of the vaccine. We know that early childhood infections have an enduring impacts on protection for influenza, but the exact details of how this works are unknown. So for example, a question that we're interested in is, does the number of past infections with a subtype of virus that you were infected with such as H1N1 one vs H3N2 encountered in the past play a role in vaccine effectiveness?
Leigh Precopio: Is there anything else that you would like to add today?
Nicole Hood: Yeah, I think really what I want to relay is that the benefits of the current influenza vaccination can be increased by improving vaccine coverage, which in this study was less than 50% among control group children who sought care for acute respiratory illness. Additionally continued monitoring of VE in children and maximizing benefits of the current vaccines by increasing vaccine coverage are all needed to decrease influenza-related illness among children. And then lastly, just wanted to reiterate that over the nine influenza seasons included in this study, we found that the influenza vaccine reduced the risk of influenza infection by 46%, which occurred despite the variation in VE within individual influenza seasons in age groups, basically showing that there is substantial overall benefit from the influenza vaccine.
Leigh Precopio: Great. Thank you so much for taking the time to speak with me today.
Nicole Hood: Thank you for having me