Predicting people's decision to get vaccinated in times of Covid-19

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1. BACKGROUND AND LITERATURE REVIEW 
 
5.1 Introduction 
 
Even before the Covid-19 pandemic, people's reluctance to receive safe and 
recommended vaccines, known as vaccine hesitancy, was already a growing concern 
(MacDonald, 2015). Specifically for the development of Covid-19 vaccines, differences 
in perception of benefits, interpretation of risks, positions in society (patient, doctor, 
health worker, politician, etc.), and presentations in the media have influenced 
differently both the thinking and the behavior of individuals (Montastruc et al., 2021).  
Recent studies show that if on the one hand the acceptance of the vaccine is mainly 
explained by the personal interest in protecting oneself against Covid-19, on the other 
hand, the vaccine hesitancy is mainly explained by concerns about side effects (Arce et 
al., 2021). Moreover, the calculation of risk and greater or lesser collective 
responsibility for vaccination decision-making is influenced by the level of public 
health of the place where you live. To give an example, most of the participants of a 
study conducted in Africa in 2020 would be vaccinated against Covid-19 if it were 
deemed safe and effective. As numerous infectious diseases cause thousands of deaths 
each year but are preventable with vaccines, the perception of the need and value of 
vaccines is increased. High-income countries, on the other hand, have successfully 
eradicated most vaccine-preventable diseases so they have not seen the devastating 
effects of these. As a result, this could lead to complacency, to altered risk calculations, 
and limited collective responsibility regarding vaccination decision-making 
(Machingaidze & Wiysonge, 2021). However, it is important to note that the intention 
to get vaccinated expressed during an interview with a participant may not always 
translate into the actual choice to get vaccinated (McEachan et al., 2011).
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5.2 Epidemiology  
 
The World Health Organization defines epidemiology as “the study of the distribution 
and determinants of health-related states or events (including disease), and the 
application of this study to the control of diseases and other health problems. Various 
methods can be used to carry out epidemiological investigations: surveillance and 
descriptive studies can be used to study distribution; analytical studies are used to study 
determinants” (www.who.int). Starting from this definition, we could therefore ask 
ourselves why a particular type of disease develops in some people and not in others. 
Diseases, as epidemiology tells us, are not randomly distributed in populations but 
rather each individual has characteristics that either predispose or protect against certain 
health conditions. These traits may depend on both genetics and environmental factors. 
Indeed, human disease is the result of the interaction between the human host, which 
must be susceptible, the infectious agent, and the environment that promotes exposure 
(Gordis, 2013).  
 
Epidemiology aims to identify the etiology of a disease, the relevant risk factors, and 
how this is transmitted to allow an intervention aimed at reducing morbidity and 
mortality due to this disease. In short, it is the basis of prevention programs (Gordis, 
2013). 
Pointedly, epidemiology is a discipline that has evolved through the constant changes in 
society and the emergence of new diseases. This evolution has allowed epidemiology to 
remain a relevant tool for understanding diseases and health events (Frérot et al., 2018). 
Indeed, it is among the main tools used since the beginning of the pandemic due to 
Covid-19 - SARS CoV-2 is its clinical expression - since it allows for closely 
monitoring the epidemiological properties (Bulut, & Kato, 2020). 
 
Coronavirus disease is an infectious disease caused by the SARS-COV-2 virus 
(www.who.int). It first appeared in December 2019 in the city of Wuhan, China 
(Ceylan, 2020). Most people infected with the coronavirus experience mild to moderate 
respiratory disease and recover without the need for special treatment. However, some 
become seriously ill and require medical attention. The greatest likelihood of
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developing serious illness after coronavirus infection is for older people and people with 
underlying medical conditions such as cardiovascular disease, diabetes, chronic 
respiratory disease, or cancer (www.who.int). 
 
On January 30, 2020, the World Health Organization declared that the epidemic due to 
Covid-19 is an emergency for international public health, and on March 11, 2020, it 
declares the state of pandemic (www.who.int). As of April 2020, more than 1.9 million 
cases of Covid-19 have been confirmed worldwide and deaths were over 120,000 
(Ceylan, 2020). 
 
In Italy, on 10 March 2022 at 00:30, the Ministry of Health published a new decree on 
the site that limits the movement of people, closes any social, recreational, and cultural 
center (including schools), and prohibits any gathering. The only businesses that can 
remain open are supermarkets and pharmacies which must ensure a distance of at least 1 
meter between customers. These unprecedented measures had the objective of 
containing the Covid-19 epidemic which saw the number of total deaths soar by almost 
100% in the 48 hours preceding the decree (Lazzerini, & Putoto, 2020). 
If we were to compare the numbers of cases diagnosed in China and Italy in the same 
period, i.e., until March 2020, we would see that there are no significant disparities: 
85,000 cases in Italy against 80,000 cases in China. However, there is an important 
disparity in the number of deaths caused by Covid-19 in the same period in the two 
countries: 10,000 in Italy against 3,300 in China. This data shifts the focus of the 
investigation to other factors, in addition to the severity of the virus, that is, 
demographic data, sociological interactions, the availability of medical equipment, 
variants of immune proteins, and virus mutations (Rubino et al., 2020). 
Covid-19 has been defined as a new type of coronavirus that spreads rapidly, from 
person to person, and becomes a major epidemic that causes a great tragedy as the 
disease has a very dynamic structure (Ceylan, 2020; Wang et al., 2020). 
In April 2020, the deaths due to Covid-19 were 123,010 in the world and the cases 
diagnosed were 2 million. Certainly, it must be considered that the official number of 
cases varies according to the differences between countries in epidemiological
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surveillance. What is certain, to date, is that Covid-19 has spread all over the world 
(Ceylan, 2020). 
Precisely for this reason, it is necessary to control the disease’s spread rate and to plan 
effectively the infrastructures and health services. In order to manage and direct the 
demand to the health system, it is essential to have an estimate of the total cases but also 
to predict possible new cases in the future to have the necessary resources available to 
deal with the epidemic. In fact, estimating the expected load is essential to timely 
manage the challenges that Covid-19 presents to public health worldwide (Ceylan, 
2020; Zhang et al., 2020). Undoubtedly, vaccination is one of the tools useful for this 
strategy (www.who.int).  
 
5.2.1 The vaccines  
 
As of December 2020, there were over 200 covid-19 vaccine candidates under 
development. Generally, vaccines are evaluated before they are found to be safe and 
effective. For example, about 7 out of 100 vaccines will be considered good enough to 
move from laboratory and animal studies to human studies. Of these, 1 in 5 are 
successful. However, having many different vaccines in development increases the 
chances that there will be more successful vaccines (www.who.int).  
 
There are three different approaches to designing a vaccine and the differences lie in the 
use of the virus or bacterium. Specifically, the first technique uses the whole virus or 
bacterium, the second one uses the subunits i.e., only the parts of the germ that trigger 
the immune system, and the third approach uses only the genetic material that provides 
the instructions to produce specific proteins and not the whole virus (www.who.int). 
 
1) The whole-microbe approach presents three different sub-approaches:  
a. Inactivated vaccine 
This technique takes a disease-carrying virus or bacterium and inactivates it using 
chemicals, heat, or radiation. This is how flu vaccines are made, for example. However, 
this technique requires special laboratory facilities to grow the virus or bacterium safely
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and the production time can be relatively long. In addition, the administration will 
require two or three doses. 
b. Live-attenuated vaccine 
This technique uses a living but weakened version of the virus. The trivalent vaccine is 
one example, namely the measles, mumps, and rubella vaccine. This approach uses 
technology similar to the aforementioned vaccine and can be produced on a large scale. 
However, vaccines like this may not be suitable for those with compromised immune 
systems. 
c. Viral vector vaccine 
This technique uses a safe virus to deliver proteins of the germ of interest so that it can 
trigger an immune response without causing disease. To achieve this, the instructions 
for creating particular parts of the pathogen of interest are inserted into a safe virus that 
acts as a vector to carry the protein into the body. This protein triggers the immune 
response. For example, the Ebola vaccine is a viral vector. 
 
2) The subunit approach:  
The subunit vaccine uses only the specific parts of a virus or bacterium that the immune 
system needs to recognize. This vaccine neither contains the entire microbe nor does it 
use a safe virus as a vector but can be composed of proteins or sugars. Most vaccines 
dedicated to childhood are subunit vaccines that protect against diseases such as 
pertussis, tetanus, diphtheria, and meningococcal meningitis. 
 
3) The genetic approach (nucleic acid vaccine): 
Unlike the other vaccines just explained, this is a nucleic acid vaccine that uses only a 
section of genetic material that provides instructions for specific proteins instead of 
using the entire microbe. The cells of the human body produce proteins starting from 
the instructions of DNA and RNA, then the DNA is transformed into messenger RNA 
which is then used as a model to produce specific proteins. The nucleic acid vaccine 
provides a specific set of instructions to our cells in both DNA and mRNA to make the 
specific protein we want our immune system to recognize and, consequently, want it to 
respond to.