Royaam Ahmad
Beyond Efficacy Numbers: Navigating the Nuances of Vaccine Effectiveness
Abstract: Vaccine effectiveness extends far beyond efficacy numbers, hinging on diverse factors suchas immune response, strain variation, and population characteristics. This study explores thefeasibility of a standardized system for measuring vaccine effectiveness by aiming to addressthe complex interplay of these factors. Employing a qualitative analysis of secondary sources,the research seeks to formulate a hypothesis for the question through inductive reasoning.The discussion emphasizes the multifaceted nature of vaccine effectiveness, mentioningimmune response, herd immunity, variant strains, and population characteristics.While mathematical models offer promise, they do not apply nicely due to the nuanced nature ofvaccine effectiveness. Instead the study brings forth a theoretical framework, integratingvaccine characteristics, target population attributes, vaccination execution factors,epidemiological dynamics, and behavioral/social influences. This formula of 5 interconnectedpoints is aimed at providing a more nuanced understanding of vaccine effectiveness. However, itremains subordinate to the evolving nature of vaccine research.
Introduction
Vaccines are one of our most forefront kinds of public health intervention when it comes toinfectious disease. A vaccine, at its core, is a less potent form of a pathogen (disease causingagent), introduced into the body so it can trigger and essentially “train” the natural immuneresponse. Two of the subject terms of this paper are Efficacy and Effectiveness. Vaccine3Efficacy (VE) is measured in a controlled clinical trial and is based on how many people whogot vaccinated had an immune response compared with how many people who got a placebo(dummy vaccine) and still developed an immune response. Conversely, Vaccine Effectiveness(VEff) reflects the real-world impact, capturing how well a vaccine protects against disease ina broader population under everyday conditions. The aim of this study is to delve into thenuances and give more structure to the latter concept
Literature Review
There is much existing research on what factors into the overall practical effectiveness of avaccine besides the efficacy numberOne of which is the immune response itself. Vaccine efficacy trials assess the development ofantibodies (the response) against a specific pathogen (the trigger, in our case, the vaccine).However, the quality and durability of the immune response can vary among individuals,impacting real-world effectiveness as factors like age, sex, underlying health conditions, andprior infections do influence immune response (Huang et al., 2021).Then comes the fact that immunity itself is not a constant. Vaccine efficacy trials oftenmeasure effects for a defined period. However, vaccine induced immunity may wane overtime, requiring booster shots to maintain effectiveness. This is also the reason vaccines likethe one for Influenza need to be revamped year after year. (Monto et al., 2005)The phenomenon of Strain Variation is yet another grey spot in measuring VEff. Vaccines aredesigned to target specific antigens of a pathogen. However, mutations and genetic changescan bring variation in the pathogen’s genetic code, giving rise to variants, known as “strains”,which in turn can potentially reduce vaccine effectiveness years down the line as a vaccinemay have only been made for the original strain. (Rose & Singer, 2008)4Population Characteristics: Factors like socioeconomic privileges, access to healthcare, and adherence or lack thereof to vaccination schedules can influence vaccine effectiveness with indifferent populations. Another factor worth mentioning here is Herd Immunity, in which themore members of a population are immunized against a disease, the safer the wholepopulation is, inclusive of non-immunized individuals.What can be gathered from this is that there seems to be a reasonably clear picture of themany factors that can determine how effective a vaccine turns out to be, efficacy being one ofthem. This variety begs the question of whether there is a way to reliably account for all suchfactors when talking about the effectiveness of a vaccine or not. That is the question thisresearch will aim to answer.What would a standardized system for measuring vaccine effectiveness be like?
Methodology:Owing to the non-contemporary nature of the topic, a qualitative analysis using data fromsecondary sources was chosen as the appropriate approach. Information was collecteddirectly from a database of existing primary and secondary literature, making use of literaturemapping to find relevant articles with varying degrees of content overlap, and to look atpotential knowledge gaps. Once a gap was found and a research question was formulated, theintent was to use inductive reasoning to form a hypothesis for the question via qualitative synthesis.
Discussion:One fact remained prominent throughout the literature review, the multi-faced nature of vaccine effectiveness. While efficacy trials provide valuable information, they are just one5pieces of the puzzle. Considering such factors as immune response, herd immunity, durationof protection, variant strains, and population characteristics paints a more complete picture ofa vaccine’s real-world impact.The question is how to do that. What way is there to take into consideration as many factorsas possible before reporting a number? Ideally, the case calls for a mathematical model toincorporate said factors into the process of coming up with a VEff Number. To that effect,Sagy et al. (2023) conducted a study on Real World Effectiveness of Single-Dose MonkeypoxVaccines, in which they accounted for predisposition to clinical as well as socioeconomic riskfactors. Taken verbatim from their paper, “We used a Cox proportional hazards regressionmodel with time-dependent covariates to estimate the association between vaccination andmpox while adjusting for sociodemographic and clinical risk factors.” (Sagy et al., 2023). Itwas a longitudinal cohort study that followed the participants over a 90 day period. Theyfound VEff to be at 86% however, in the same paper, the authors note that this was apreliminary finding and more research is needed. Further, a 90 day period does not pan out tobe long enough when faced with changes in immune response or vaccine sensitivity that aregenetic in nature and may manifest with no proper trend. It would seem that there are simplytoo many factors, and incredibly nuanced ones at that, to make a universally applicable modelfor computing effectiveness.The next best case would be a comprehensive theoretical model. The problem is amultifaceted one so it is better tackled with a multifaceted solution. If we can establish anumber of points such that they cover most of the discussed factors, it could help us get abetter glimpse of ground level VEff. Keeping in mind the articles reviewed and the pointsestablished so far, the following five points can be synthesized to be the cornerstones of the model.
Vaccine Characteristics: This aspect is about the properties of the vaccine itself, factoring inits ability to trigger an immune response (immunogenicity), the strength and duration ofresponse, and any potential side effects.
Target Population: The individuals receiving the vaccine, as factors such as age, underlyinghealth conditions, and prior exposure to the disease all influence how well a vaccine worksfor an individual.
Execution Factors: This aspect relates to the implementation of a vaccination program.Focusing on vaccination coverage (the percentage of the population vaccinated), making suredoses are delivered at the right time with the right interval, and the appropriate handling ofthe vaccine in logistic settings.
Epidemiological Dynamics: Considering the characteristics of the disease itself and itstransmission patterns. Ease of spread, emergence of new variants, herd immunity, et cetera.
Behavioral and Social Factors: Comprising the societal context surrounding vaccination.Vaccine hesitancy, the anti-vaxx sentiment, access to healthcare services, misinformation areexample of social or behavioural elements that influence vaccination rates and in turn,vaccine effectiveness.This 5-point formula relies on the interconnectedness of its points to encapsulate the array offactors that govern effectiveness of a vaccine. For example, a vaccine’s immunogenicity (howmuch of an immune response it triggers) can influence its effectiveness in different agegroups. High vaccination coverage contributes to herd immunity. Conversely, vaccinehesitancy can lead to lower coverage, weakening overall effectiveness. Thus the points tieback to themselves to establish a cohesive formula to guage VEff figures better, assisting inboth understanding and navigating shifts in effective vaccination.7That said, it is pertinent to acknowledge that this is an evolving model and research onvaccines is always advancing. This model only aids us to see and understand ground levelvaccine effectiveness for what it is, a complex idea with multiple interconnected layers to it.
Conclusion:Reiterating the research question of whether a standardized system to measure vaccineeffectiveness is feasible or not, this study finds the answer to be in the affirmative thoughcloser to more of a theoretical framework rather than a robust mathematical model. Vaccineeffectiveness is a nuanced phenomenon with multiple increasingly nuanced aspects. Ageneral-yet-specific approach like the 5 point formula in this study seems a reasonable way totackle an issue of such nature.
Author is student of Forman Christian College University