To Vaccinate or Not to Vaccinate? That is (Not) the Question

INDIVIDUAL BEHAVIOR STRONGLY INFLUENCES THE OUTCOME OF PREVENTIVE STRATEGIES. UNDERSTANDING THE BEHAVIORAL AND SOCIAL DYNAMICS BEHIND THE PERSONAL DECISION OF NOT GETTING VACCINATED IS THE GOAL OF THE IMMUNE PROJECT, WINNER OF AN ERC GRANT

by Alessia Melegaro, Director of the Covid Crisis Lab, Bocconi University

The COVID-19 pandemic has caused enormous morbidity and mortality globally with over 90 million cases and almost 2 million deaths as of 15 January 2021. The licensure and distribution of effective vaccines that allow societies to achieve sufficient immunity to stop the exponential spread of the disease are therefore widely seen as necessary for a speedy return to pre-pandemic practices. As of today, there are 64 vaccines in clinical trials on humans, with 3 already approved and 20 in phase 3 trials. As the first vaccines have been approved both in the US and in Europe, scientists have turned to two key questions: how the initially scarce vaccine should be distributed within and between countries and, secondly, how individuals will respond to the vaccination campaign - will vaccine hesitancy movements hinder the success of this global vaccination effort?
 
So far, a great deal of this focus has been on prioritization within countries, identifying those groups in the population that should be vaccinated first, either because they belong to that category of people who have been taking care of all of us, with commitment and altruism for an entire year, or those that are fragile and at increased risk of complications. However, there is a perhaps equally important question about how to allocate the available vaccines across countries when they are closer to herd immunity levels, and whether cooperative behavior will be more effective in keeping the spread under control within the country. Many countries are taking steps to ensure that they would have adequate supplies of the vaccine for their population. But, the optimal strategy for securing vaccine supplies and balancing the global-interest with individual countries’ self-interest is unclear and there might be scenarios in which one country has reached the threshold for domestic herd immunity, and it then may find it optimal to donate doses to other countries with lower vaccination coverage, as this would allow for a sharp reduction in the inflow of infected individuals from abroad.

Another critical aspect that need to be considered is the potential effect of Covid19 vaccine refusal on the implementation of the biggest vaccination campaign ever. Vaccine hesitancy, delays in adhering to the immunization schedule have been seen as a raising phenomenon in the past decade and have generated the re-emergence of vaccine preventable diseases (VPD) which could have been eradicated long time ago. Vaccine hesitancy is defined as “a delay in acceptance or refusal of vaccines despite availability of vaccination services”, fueled by the widespread misperception that many serious infections no longer circulate or that vaccines themselves are dangerous. Indeed, after decades of successful immunization activities, low incidence rates associated with VPD have decreased public concerns with respect to infectious diseases. This phenomenon has the potential to undermine benefits of past and current immunization efforts and will surely affect the pace at which the Covid19 pandemics will be defeated or not, similarly to what happened with other epidemics from the past.
 
More generally, human behavior with respect to vaccines and other preventive or containment strategies - such as self-isolation, masks and social distancing - are all the result of a number of complex individual and societal factors, poorly understood, that strongly affect individual’s compliance to the recommended policies and, as a consequence, their overall effectiveness. The IMMUNE project, funded by the European Research Council, will dig into these topics with the aim to shed light on the dynamics of human behavior with respect to vaccination decision and, more generally, infectious disease preventive measures. This will mean studying the determinants of individuals’ behavior, including background socio-demographic characteristics, epidemiological and context-specific aspects, exposure to peer influence and to specific communication narratives. By doing this we are going to break new ground in the understanding of these mechanisms and to fuel the epidemiological framework with new hitherto unknown elements that are essential to capture the potential risk associated with new or past infections. To achieve these objectives, we will also leverage social media and new survey data, gathering a more in depth understanding on how individuals’ decisions are being made. This will allow us to design and implement an innovative class of epidemiological models which will embed dynamic human behavior and its interdependencies with the infection’s process itself.
 
In the past year we have all witnessed the importance of individuals’ actions with respect to the spread of the SARS-Cov-2 infection. We have seen the effect of compliance (or non-compliance) and the value of altruistic (vs. selfish) actions to keep the spread under control. Now, with the IMMUNE project, there is the possibility of breaking new ground in the understanding of these processes and of giving rise to a novel and comprehensive framework which stands at the intersection of different but strongly interconnected disciplines. This IMMUNE project will become the hub around which scientists from different research areas can share their findings and expertise and the framework we will generate will be a powerful instrument when dealing with the current and future epidemiological challenges we will have to face.