Selective Vaccination Could Suffice to Develop a Robust Herd Immunity against SARS-CoV-2
This study proposes a balanced and combined use of immunity developed from vaccination and natural infection. This work reviewed literature and enriched further using critical thoughts on integrating vaccination with naturally-induced immunity. Undoubtedly, coronavirus is an extraordinary challenge the present-day world has faced. However, efforts have been in place to vaccinate a significant proportion of the global population. The question is, which preventive strategies need to be adopted to be on the safest side? Thus, should we keep pushing towards mass vaccination, or shall the less vulnerable group of the population remain unvaccinated (contingent on their willingness) to develop naturally-induced immunity? Many factors such as sex, comorbidities, age, and lifestyles underlie the impact of the coronavirus. Robust predictive models that capture most of the variation explained by the underlying factors are vital to developing. Based on the models, coronavirus-resilient individuals might be unvaccinated to develop natural immunity, while the susceptible ones get vaccinated. It might be rational to vaccinate susceptible segments of the global population while leaving the resilient ones to choose between getting vaccinated or developing natural immunity. However, this strategy was proposed for coronavirus and might not work for all diseases.
Coronavirus, Mass vaccination, Natural infection, Trade-offs, Underlying factors
Coronavirus is an extraordinary challenge the contemporary world has faced [1,2]. Huge resources have been mobilized and promising containment strategies have been invented and adopted to reduce the lethal impacts of coronavirus. A consensus was reached to develop robust immunity against coronavirus . Accordingly, besides non-pharmaceutical interventions such as social distancing, personal hygiene, the use of personal protective equipment, excellent efforts have been made and the-state-of-art technologies and huge resources have been mobilized to develop potent vaccines.
Nevertheless, like other diseases, infection from coronavirus produces a continuum of susceptibilities ranging from asymptomatic to lethal cases. Several underlying factors for the disparity in the severity of coronavirus have been identified such as comorbidities , sex/gender , age , and living standards and lifestyles . This disparity calls for the invention of a range of preventive strategies to save resources and lives while maintaining robust natural immunity acquired by a significant proportion of the global population.
This piece of work specifically deals with the importance of vaccinating all or most people irrespective of their susceptibility to coronavirus. For example, in those groups who are expected to show asymptomatic to mild cases leaving them to their discretion to develop natural immunity may suffice. This strategy however requires mass testing for coronavirus and extensive documentation of the health history, and demographic characteristics of the global population. Moreover, it is high time to develop a robust model to predict the impact of predisposing factors to identify individuals that are expected to be resilient to coronavirus. This strategy could enable us to maximize the best use of herd immunity developed from both vaccination and natural infection.
This piece of work was based on literature review and critical thinking and synergizes the proper combination of vaccination-triggered and naturally-induced immunity to resolve the significant level of hesitancy observed against coronavirus vaccination.
Efforts have been made to summarize the advantages of vaccination and natural infection to combat the negative impact of the coronavirus, the trade-offs of these preventive strategies, and the pressing need to develop prediction models that determine the level of resilience/susceptibility using health records and demographic data.
Snapshots on the epidemiology of SARS-CoV-2 infection
Two years have been passed since most nations infected by the coronavirus. The coronavirus might have been widely spread especially following the ease of the lockdown and social distancing. The spread of the coronavirus could be higher in overcrowded settings and congested villages and shantytowns-typifying the lifestyle of most of the less developed world citizens. However, although there might be a significant variation in infection and fatality rate associated with coronavirus the impact of the pandemic in less developed countries is not as much as it has been frightened of. The importance of naturally-induced immunity possessed presumably by most of the less developed world citizens and a significantly high proportion of developed nations' inhabitants could not be overlooked while planning to build herd immunity against the coronavirus pandemic.
Both natural infection and vaccination induce immunity
Both natural (wild) infection and vaccination produce antibodies. However, the amount and efficacy of antibodies produced may vary depending on the rate of infection (generally contracting more antigens elicits a robust response). Both mass vaccination and natural infection confer herd immunity - a phenomenon in which a sufficient proportion of the population is protected against the pathogen - at this stage, the spread of the virus could be meaningfully contained . However, the question is at what cost and which one, i.e., natural infection or vaccination could produce robust immunity and might have a long-lasting positive impact on global health?
Natural immunity has evolved and refined itself in the course of its history. It might be due to this fine-tuned efficacious natural infection confers a stable and highly persistent immunity  and does not bring many more reinfections . Vaccines sometimes may produce an off-target effect because natural killer (NK) cells and monocytes of innate cells need to be exposed to certain pathogens to develop a trained phenotype . Often a single natural infection induces immunity but this often requires repeated vaccinations (even a booster). Mass immunization may bring unforeseen, and long-term complications .
Natural immunity is long-lasting and has a broad effect . Natural infection is scrutinized by all the body's defense lines, however, for example, a vaccination performed by direct injection into the bloodstream bypasses much of the body's defense routes, which may produce weak immunity . Vaccines recognize a new variant of the contagion in question at a reduced rate . The natural infection with the influenza A/H1N1 (pH1N1) virus has produced a better immune response than induced by a monovalent pH1N1 vaccine . Vaccines as in the case of influenza A virus could last effective for a short time and confer a narrow-based immunity . Immunity resulting from natural infection can curb pandemics, nevertheless, it does not eradicate diseases, therefore, it has to be accompanied by the effective use of potent vaccines .
Developing herd immunity through natural infection only may require unbearable sacrifices . Normally vaccines develop a mild to moderate infection , which makes them less risky. The high purity of the specific protein in the vaccine  leads to a better immune response than natural infection. However, vaccines administered via the oral or as a nasal spray may serve better than the ones administered intramuscularly as they provoke the immune system starting from the naso-oral cavity.
Illness may be encountered from natural infection in susceptible individuals. For most immunities, standardized vaccines not only are safer but produce a more robust response . This efficacy, for example, includes vaccines for HPV, tetanus, and pneumonia . Unlike the unintended acquisition of natural immunity, clients can choose when to get vaccinated. While natural immunity provokes a range of responses, vaccines are designed to create the most significant immune response. Because vaccines are made using parts of the viruses and bacteria that cause disease, the active component of the vaccine that induces immunity is natural. However, other ingredients in vaccines or the route of administration are unnatural .
Modeling of predisposing factors
Given the ever-increasing high accumulation of global coronavirus-associated data and the state-of-art computational technologies and skills, the effect of underlying factors can be determined by using robust models and this, in turn, enables to predict susceptibility at the individual's level.
It is high time to research the disparity in susceptibility to coronavirus to uncover those social and biological factors conferring resilience/susceptibility to pandemics of these types. Therefore, it might be advisable to vaccinate susceptible segments of the global population while leaving the resilient ones to choose between getting vaccinated or acquiring natural immunity.
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Takele Taye Desta, Department of Biology, College of Natural and Computational Science, Kotebe University of Education, Addis Ababa, Ethiopia
© 2022 Desta TT. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.