Understanding Immunity and the Challenges of COVID-19 Variants
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Chapter 1: The Role of Antibodies in Immunity
Antibodies against the virus responsible for COVID-19 are crucial for achieving immunity. If long-lasting immunity is unattainable, SARS-CoV-2 could emerge as a recurrent virus, affecting the global population annually.
SARS-CoV-2, classified as an RNA virus within the coronavirus family, represents one of 36 RNA virus families responsible for human diseases, yet we only possess vaccines for 10 of them. In certain cases, the viruses do not lead to severe illness, eliminating the incentive for vaccine development. In other instances, creating effective and safe vaccines has proven difficult. While some vaccines, like those for polio, offer long-lasting immunity, others, such as the flu vaccines, require regular updates to maintain effectiveness against new strains. Currently, it appears unlikely that a safe and effective vaccine for SARS-CoV-2 will be available in the near future.
Section 1.1: Understanding Virus Mutation
The replication of genetic material is inherently prone to errors, resulting in mutations. The rate at which a virus mutates is influenced by its replication process and its ability to correct introduced errors. RNA viruses typically mutate more rapidly than their DNA counterparts. Although coronaviruses mutate more slowly than other RNA viruses due to their proofreading enzymes, the potential for mutation remains.
If SARS-CoV-2 does not evolve into a less harmful form, it is probable that most individuals will eventually encounter the virus. As seen during the ongoing pandemic, some will experience severe illness, some may succumb to the virus, and others will only exhibit mild symptoms. Dr. Michael Ryan from the World Health Organization (WHO) has suggested that SARS-CoV-2 may become endemic, similar to certain influenza strains, indicating that the virus could circulate within the global population, resulting in annual infections. As Dr. Ryan stated in a press briefing on May 13, 2020, "This virus may never go away."
Subsection 1.1.1: Developing Immunity Post-Infection
If the immune response generated from viral exposure is effective and the virus does not mutate to evade this response, individuals who recover from COVID-19 could naturally acquire some degree of immunity. This immunity may either prevent reinfection or mitigate the severity of symptoms for a certain duration.
However, it remains uncertain how many individuals will develop immunity and the longevity of that immunity. It is well-established that SARS-CoV-2 is undergoing mutations, as is typical for viruses. Not all changes in the viral RNA alter its proteins, and some mutations may not impact protein function or the immune system's ability to recognize the viral proteins. Nonetheless, some mutations could change protein function or the immune recognition process.
Given that some individuals may lose immunity over time due to viral changes, the challenge of developing a vaccine remains significant, particularly as mutations in viral proteins critical for immune response can hinder vaccine effectiveness.
Section 1.2: The Impact of Mutations on Virus Virulence
Tracking the amino acid mutations in SARS-CoV-2 reveals significant variations. The x-axis indicates the number of mutations, with colors representing different countries from which patients have been isolated. Each circle corresponds to the viral sequence from a specific patient. At the time of this analysis, two viral strains exhibited over 20 mutations compared to the initial sequenced strain.
Mutations not only influence immunity but can also affect the virus's virulence—the capacity to transmit and cause illness. Research indicates that certain mutations may enhance virulence, while others could reduce it. A preprint study published on medRxiv found variations in virulence when cultured cells were infected with viruses exhibiting different mutations. Some of these mutated viruses displayed increased virulence, while others were less virulent or intermediate.
Chapter 2: The Path to Achieving Herd Immunity
To establish any form of immunity without vaccination, individuals must contract SARS-CoV-2. By curtailing the pandemic's spread, the global community has successfully minimized COVID-19-related deaths and provided healthcare systems the opportunity to enhance their capacity for patient care. However, this containment has also slowed the potential development of natural immunity within the population.
Population immunity, often referred to as "herd immunity," represents the proportion of individuals who must be immune to a pathogen to prevent widespread transmission. This threshold varies based on the average number of secondary infections produced by an infected individual. Vaccination is a proactive approach to achieving herd immunity, especially for SARS-CoV-2, where scientists estimate that around 50–70% of the population will need immunity.
Research into antibody and T cell responses to SARS-CoV-2 will be vital in determining the feasibility of herd immunity and guiding vaccine development.
This video titled "Is COVID-19 Dysregulating Our Immune Systems?" explores the complexities of how COVID-19 interacts with our immune responses and the implications for immunity.
In the video "What causes a virus to change and how to stop stronger Covid-19 variants from emerging," experts discuss the dynamics of viral mutation and strategies to curb the emergence of more potent variants.