PANDEMICS AND EPIDEMICS: EMPHASIS ON COVID-19

Ferreira C. Pandemics and epidemics: Emphasis on COVID-19. International Journal of Infection. 2025;9(1):14-16.

C. Ferreira^*

Biophytis Sorbonne, Paris, France.

*Correspondence to:
Claudia Ferreira, MD, PhD,
Biophytis Sorbonne,
Paris, France.
e-mail: claudia.ferreira@biophitis.com

Received: 02 April, 2025 Accepted: 31 April, 2025

ISSN 1972-6945 [online] Copyright 2025 © by Biolife-publisher This publication and/or article is for individual use only and may not be further reproduced without written permission from the copyright holder. Unauthorized reproduction may result in financial and other penalties. Disclosure: all authors report no conflicts of interest relevant to this article.

ABSTRACT

A pandemic is a contagious infection that spreads globally throughout the world population, without any border, while an endemic is an infection that extends to just a part of the world population. An epidemic results from the rapid spread of a disease to a large number of people in a given population in a short period of time. In this century, there have been several pandemics and epidemics that have afflicted humanity such as coronavirus disease of 2019 (COVID-19), Ebola, Zika, Middle East respiratory syndrome (MERS), and H1N1, also known as swine flu. These contagious infections activate both the innate and adaptive immune systems. The excessive immune response can cause severe inflammatory damage that can lead to death of the patient. Here in this paper, we review the pandemics and endemics which occurred in the 21st century and discuss the vaccinations used to prevent them.

KEYWORDS: Pandemic, endemic, epidemic, infection, COVID-19

INTRODUCTION

A pandemic is an epidemic that spreads rapidly and extends on a very great scale to involve a large part of the world’s population. The word pandemic derives from the ancient Greek word πανδήμιος, or pandḗmios, which means “of all people”. An endemic is a disease that is constantly present or very frequent in a population or territory for various causes, while an epidemic is defined by the rapid spread of a disease to a large number of people in a given population in a short period of time (1) (Table I). The term pandemic applies only to contagious diseases or conditions. A human pandemic occurs when there is a lack of immunity to a highly dangerous pathogen.

Table I. Pandemics and epidemics since the 19^th century.

In the 21st century, several pandemics have occurred, such as coronavirus disease of 2019 (COVID-19) (the most recent), along with other global or regional outbreaks, such as H1N1 (also known as swine flu), Ebola, Zika, and Middle East respiratory syndrome (MERS) (2).

In pandemic or endemic diseases, viral infection activates innate and adaptive immunity (3). Innate immunity mediated by phagocytic cells is the body’s crucial first line of defence in combatting infections and adaptive immunity is activated afterwards with viral activation of T and B lymphocytes.

DISCUSSION                                                                                                                                                                                          

Innate and adaptive immunity play a key role in slowing and stabilizing pandemics towards endemics (4).  Natural immunity and vaccines reduce severity, although reinfections remain likely. The study of anticipating pandemics and endemics helps us prevent these pathologies that could emerge, evolve or become serious.

The most recent pandemic that has occurred is COVID-19, which was initiated in China in December 2019 by the SARS-CoV-2 virus. Adaptive immunity is characterized by the participation of antibodies and T cells that generate memory, but with SARS-CoV-2, sterilizing immunity against infection declines faster than protective immunity. The immunological aspects of the pandemic have played an important role in influencing the generation of vaccines and improving already existing therapies. The rapid development of a vaccine has highlighted the importance of long-term immune memory that provides protection. During COVID-19, many young adults presented more severe symptoms due to a more vigorous immune response, even if the incidence of mortality was lower than in the elderly. Some elderly individuals showed partial immune protection due to previous exposures to similar viruses (5). During the pandemic, significant attention was paid to COVID-19, neglecting other pathologies that occurred in the hospital, which affected human immunodeficiency virus (HIV) patients regarding the execution of clinical tests and diagnosis. HIV prevention is crucial and the Centers for Disease Control and Prevention (CDC) recommends that all adolescents and adults from 13 to 64 years of age be tested at least once and patients who are at increased risk for HIV should be rescreened.

The SARS-CoV-2 virus responsible for COVID-19 disease has caused more than 12,000 deaths in Africa, surpassing the total number of people who died during the Ebola epidemic. Ebola virus and SARS-CoV-2 originated from zoonotic spillovers (transmission from animals to humans), with natural reservoirs in bats (6). For Ebola, the intermediate vehicles are primates and rodents, while for SARS-CoV-2, it is the pangolin (not yet confirmed). Ebola is a disease caused by a negative-stranded RNA filovirus, that causes massive vomiting and diarrhea and spreads among individuals who have close contact. Ebola causes severe immune system dysfunction with tissue damage and systemic inflammation. Treatment involves the use of viral vector vaccines and immunotherapy with monoclonal antibodies as emergency treatment.

COVID-19 has often resulted in an excessive and damaging immune response with the formation of inflammatory cytokines which cause a cytokine storm that is mostly mediated by TNF, IL-6 and IL-1. mRNA vaccines are one of the most relevant scientific innovations of the 21st century. COVID-19 vaccines were mainly produced by Pfizer-BionTech and Moderna and were approved by the Federal Drug Administration (FDA) and the European Medicines Agency (EMA) for global use against SARS-CoV-2. Patients with Ebola and long COVID-19 can develop similar chronic complications such as neurological disorders, anxiety/depression, joint pain, hearing problems, psychological disorders, fatigue and others (7).

Vaccines are one of the best public health tools ever developed and their usefulness is extraordinary. However, immunity does not guarantee the disappearance of the virus, which will continue to evolve and will require targeted vaccinations, genomic surveillance and sensitivity to antigenic dynamics (8). Vaccines prevent serious or fatal diseases, such as polio, measles, hepatitis B, meningitis, tetanus, whooping cough and COVID-19. As immunity increases (from infections or vaccines), transmission slows and an endemic equilibrium with seasonal oscillations is reached. COVID-19 appears to be becoming endemic, with regional outbreaks underway, but its future trajectory remains unpredictable. Vaccines protect against complications such as pneumonia, encephalitis, paralysis, and permanent damage, and reduce hospitalizations and mortality, especially among the elderly and fragile patients. During COVID-19 vaccination, it was noted that the vaccine works faster and is more effective with two doses in the same arm, compared to vaccination in both arms (9).

Once common diseases, such as smallpox or polio, have been eradicated or almost eliminated thanks to vaccination programs used globally (10). Diseases such as the plague and smallpox that were once endemic have been eradicated or controlled thanks to vaccines and public health measures. Vaccines are safer than natural infection, provide effective and long-lasting protection, even at the community level, and prevent illnesses, complications, and deaths, saving social and economic resources.

CONCLUSIONS

In conclusion, both pandemics and epidemics are transmissible infections that recur cyclically and affect various population groups. Infections activate the immune system and inflammation to cause serious local and systemic damage, as well as health and social distress.

Conflict of interest

The author declares that they have no conflict of interest.

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