1. Influenza Vaccine Immunogenicity
2. Non-inferiority Trials
3. Clinical Trial Estimands
4. Immunological Intercurrent Events
5. Vaccine Efficacy

In the ever-evolving field of influenza vaccine research, a cutting-edge study has proposed a novel method for assessing immunogenicity trials—by means of a clearly defined estimand. This new approach outlined in an article published in the prestigious journal ‘Vaccine’ could reshape the landscape of influenza vaccine approval processes and enhance our understanding of vaccine efficacy.

DOI: 10.1016/j.vaccine.2024.01.005

The concept of ‘estimands’ in clinical trials has gained significant attention following recent regulatory guidance. An estimand is a detailed strategy that specifies the exact quantity that a trial aims to estimate, and how to handle subsequent events termed as ‘intercurrent events’—key occurrences that intervene after the initiation of a trial, potentially impacting the outcome measurement or obscuring its interpretation.

A Groundbreaking Proposition for Influenza Vaccine Trials

The manuscript, authored by Jozef Nauta, revolutionizes the estimand framework specifically tailored for one of the most prevalent types of immunogenicity trials—the non-inferiority influenza vaccine immunogenicity (IVI) trial. Nauta’s background, amassing invaluable experience prior to his retirement while employed at Abbott, a pharmaceutical company producing influenza vaccines, denotes a wealth of industry insight embedded within the new strategy.

Addressing Intercurrent Events in Immunogenicity Trials

Key to this new proposal is the identification and handling of ‘immunological intercurrent events’ (IIEs) which can derail a trial’s objectives. IIEs encompass any protocol deviations that occur during the trial which can affect immunogenicity endpoints.

The proposed estimand accounts for the effects of IIEs. Such handling is crucial because conventional analysis often overlooks these events, potentially leading to skewed results. As the world faces frequent influenza outbreaks, the accuracy of vaccine efficacy data is imperative for public health decisions.

Enhanced Statistical Analysis via Multiple Imputation

The magnitude of the manuscript is not only in identifying the potential hurdles in IVI trials but also in offering tangible solutions. It recommends a multiple imputation approach to replace missing or excluded endpoint values due to IIEs with plausible values. This method hinges on the use of both mandatory predictors—indispensable for preventing biased predictions—and non-mandatory predictors, which help reduce additional variance resulting from imputing.

The article meticulously elaborates on the four steps involved in multiple imputation and lists available software that researchers can utilize. This prescriptive advice provides a blueprint for researchers and statisticians looking to improve the integrity of their IVI trial results.

Impact on Regulatory Guidelines and Vaccine Development

This estimand approach is poised to have a marked influence on regulatory guidelines for vaccine approval. Clear guidance on handling IIEs and a refined strategy for imputing missing immunogenicity data can streamline the approval process by mitigating the risks of presenting biased efficacy results.

Non-inferiority trials are fundamental in ensuring that new vaccines are at least as effective as existing vaccines. In the context of influenza, where vaccine updates are frequent due to the rapidly mutating virus, having a rigorous framework for non-inferiority assessments is crucial for timely vaccine deployment.


1. Nauta, J. (2024). Estimand for non-inferiority influenza vaccine immunogenicity trials. Vaccine.
2. Food and Drug Administration. (2019). E9(R1) Statistical Principles for Clinical Trials: Addendum: Estimands and Sensitivity Analysis in Clinical Trials.
3. European Medicines Agency. (2020). Guideline on the treatment of missing data in confirmatory clinical trials.
4. Mallinckrodt, C. H., Lin, Q., & Molenberghs, G. (2013). A structured approach to choosing estimands and estimators in longitudinal clinical trials. Pharmaceutical Statistics, 12(5), 261-266.
5. Rubin, D. B. (1976). Inference and missing data. Biometrika, 63(3), 581-592.


Advancements in the methodology of non-inferiority IVI trials could alter how future vaccines are evaluated, propelling vaccine science into a new era of precision. The estimand framework articulated by Jozef Nauta and outlined in the ‘Vaccine’ journal is a testament to the ongoing commitment to innovation in public health. As the study inspires global health regulators and researchers alike, the outcome is clear: more reliable influenza vaccines, and by extension, better-protected populations worldwide.

For readers within the medical and research community, this paper by Nauta offers a foundation for more accurate and valid clinical trial conclusions—ultimately aiming for an efficient path to protecting individuals against the ever-present threat of influenza.