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An In vitro Model to Study Immune Responses of Human Peripheral Blood Mononuclear Cells to Human Respiratory Syncytial Virus Infection
Published on: December 10, 2013
Live-attenuated Vaccines Prevent Respiratory Syncytial Virus-associated Illness in Young Children
Ruth A Karron1, Jessica E Atwell1, Elizabeth J McFarland2
1Department of International Health, Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
Insights
Live-attenuated respiratory syncytial virus (RSV) vaccines show promise for infants. Promising vaccine regimens protected children against RSV-associated illnesses and primed for robust immune responses, suggesting potential to reduce disease burden.
Area of Science:
- Vaccinology
- Pediatric Infectious Diseases
- Immunology
Background:
- Active immunization is crucial for protecting infants and young children against respiratory syncytial virus (RSV).
- Live-attenuated RSV vaccines are under development as a potential preventative measure.
Purpose of the Study:
- To estimate the efficacy of live-attenuated RSV vaccines in young children.
- To assess the durability of antibody responses post-vaccination and after natural RSV infection.
- To determine sample sizes for future efficacy trials.
Main Methods:
- Analysis of data from seven Phase 1 clinical trials involving 239 children aged 6 to 24 months.
- Evaluation of vaccine regimens based on induced neutralizing antibody responses.
- Assessment of protection against RSV-associated acute respiratory illness and lower respiratory illness.
Main Results:
- Five vaccine regimens inducing neutralizing antibodies in ≥80% of participants were identified as "more promising".
- These "more promising" vaccines demonstrated significant efficacy: 67% against medically attended acute respiratory illness (MAARI) and 88% against medically attended acute lower respiratory illness (MAALRI).
- A ≥4-fold increase in RSV neutralizing antibody post-vaccination strongly correlated with protection, with no severe lower respiratory illness observed in such children.
Conclusions:
- Live-attenuated RSV vaccines can elicit protective immune responses in young children.
- Vaccine-induced antibody levels are associated with protection against RSV-associated respiratory illnesses.
- Further development of these vaccines could significantly decrease the global impact of RSV disease.
Abstract:
Rationale: Active immunization is needed to protect infants and young children against respiratory syncytial virus (RSV). Rationally designed live-attenuated RSV vaccines are in clinical development.Objectives: Develop preliminary estimates of vaccine efficacy, assess durability of antibody responses to vaccination and "booster" responses after natural RSV infection, and determine sample sizes needed for more precise estimates of vaccine efficacy.Methods: We analyzed data from seven phase 1 trials of live-attenuated RSV vaccines in 6- to 24-month-old children (n = 239).Measurements and Main Results: The five vaccine regimens that induced neutralizing antibody responses in ≥80% of vaccinees (defined post hoc as "more promising") protected against RSV-associated medically attended acute respiratory illness (RSV-MAARI) and medically attended acute lower respiratory illness (RSV-MAALRI) and primed for potent anamnestic responses upon natural exposure to wild-type RSV. Among recipients of "more promising" RSV vaccines, efficacy against RSV-MAARI was 67% (95% confidence interval [CI], 24 to 85; P = 0.008) and against RSV-MAALRI was 88% (95% CI, -9 to 99; P = 0.04). A greater than or equal to fourfold increase in RSV serum neutralizing antibody following vaccination was strongly associated with protection against RSV-MAARI (odds ratio, 0.26; 95% CI, 0.09 to 0.75; P = 0.014) and RSV-MAALRI; no child with a greater than or equal to fourfold increase developed RSV-MAALRI. Rates of RSV-MAARI and RSV-MAALRI in placebo recipients were 21% and 7%, respectively. Given these rates, a study of 540 RSV-naive children would have 90% power to demonstrate ≥55% efficacy against RSV-MAARI and ≥80% efficacy against RSV-MAALRI; if rates were 10% and 3%, a study of 1,300 RSV-naive children would be needed.Conclusions: Rapid development of a live-attenuated RSV vaccine could contribute substantially to reducing the global burden of RSV disease.
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