Public Health Emergence: Challenges and Prospects for the Future of Herd Immunity to Reduce the Negative Impact of Disease X in Low- and Middle-Income Countries

Dear Editor,

Worldwide health and the economy are in grave jeopardy due to the rapid spread of new diseases. Because of their potential to spread epidemics and the difficulties in putting effective control measures in place, a great number of viruses are currently threatening public health. Of these infections, “Disease X” is one. Could low- and middle-income countries (LMICs) achieve herd immunity, which protects a population from the “Disease X”?

The World Health Organization (WHO) states “Disease X” as the understanding that a severe global epidemic could arise from a pathogen that is presently unidentified as a cause of human illness. ¹ Pathogen X, an unidentified infectious agent capable of causing human illness, might potentially be the source of a future outbreak involving Disease X, which has the ability to spread rapidly and affect a large number of people, surpassing any other known pathogen. There is a concept that suggests that the emergence of a catastrophic outbreak caused by Disease X is probable due to the transmission of a very infectious RNA virus from animals to humans. This transmission is expected to occur in an area where many risk factors and population dynamics align, leading to continuous person-to-person transmission. ² The coexistence of zoonotic pathogen proliferation and the risk of laboratory errors or bioterrorism-induced pandemic infections offer bleak prospects. ³

When contemplating the potential occurrence of Disease X, it is inevitable to reflect upon recent pandemics such as COVID-19, which was caused by SARS-CoV-2 and has prompted discussions regarding its classification as the inaugural Disease X. ⁴ The COVID-19 vaccines were authorized for emergency use within 11 months of the initial publication of the SARS-CoV-2 sequence, showcasing the remarkable efficacy of scientific collaboration. By March 2023, almost 70% of the world’s population had been administered at least 1 dosage of a COVID-19 vaccination. While high-income countries (HICs) typically have vaccination rates of over 75%, just 29.9% of individuals in low-income countries (LICs) have completed their initial series of shots as of May 22, 2023. For instance, Burundi has managed to immunize a mere 0.25% of its population. Mathematical modeling endeavors aimed at quantifying the impact of this inequality suggest that 1.3 million deaths could have been averted via enhanced and fair distribution of vaccines, even in the absence of other interventions to minimize physical contact.^5,6 By October 26, 2021, about 3.84 billion people globally, which is almost 50% of the global population, had gotten at least 1 dose of the COVID-19 vaccine. However, the vaccination rate was below 3% in 24 African nations and only 0.9% in Ethiopia, which are classified as low- and middle-income countries (LMICs). ⁷ The uneven allocation of vaccinations, both within individual countries and among different nations, poses a risk to impeding the advancement toward attaining herd immunity. ⁸

Herd immunity, or population immunity, refers to the safeguarding of a population against infectious diseases. Protection can be achieved either through vaccination or by acquiring natural immunity from a previous infection. Vaccination is the preferable approach due to the significant mortality risk associated with spontaneous infection. The herd immunity threshold refers to the minimal percentage of the population that needs to be immune to a contagious disease, typically by vaccination, in order for the disease’s occurrence to either stabilize or decline. The threshold is contingent upon the disease’s level of contagion and the efficacy of the vaccines that are currently accessible. ⁹ Community delays and refusals to vaccinate limit the achievement of vaccination thresholds necessary for herd immunity, hence increasing the risk of an epidemic if a vaccine-preventable disease starts spreading in that community. ⁸

On May 5, 2023, the WHO announced that COVID-19 is no longer considered a public health emergency of worldwide concern. There is a potential for the emergence of hazardous complacency, which may lead to a sudden surge in the number of cases and fatalities. Unregulated social gatherings and public events lacking sufficient precautions may create favorable circumstances for unforeseen increases in the frequency of COVID-19 cases and fatalities. ¹⁰ It can be a significant factor in people’s reluctance about vaccinations. Also, there are debates over the possibility of greater evasion of acquired immunity from vaccinations. Subsequently, the identification of the JN.1 new variant of COVID-19 in September 2023 sparked concern for public health and safety.^11,12 There are 2 major factors that can hinder people from getting vaccinated: concerns regarding the effectiveness of the vaccination and concerns about potential side effects. Establishing trust and fostering alliances with people in the community is essential for governments, public health teams, and healthcare professionals. Ensuring the prompt and regular vaccination of vulnerable populations should be a pressing concern for any country concerned with effectively managing COVID-19 as well as other preventable diseases through immunization. ¹³ It is imperative to implement vigilant surveillance and reporting systems to track the COVID-19 situation and gather information in underserved regions of LMICs.

Following a devastating global pandemic outbreak of COVID-19 that lasted for about 3 years, the situation has now been mostly brought under control, although complete eradication has not yet been achieved. The global community was ill-equipped to effectively address this pandemic, as the disease emerged abruptly, leaving us utterly astonished. LMICs encountered numerous obstacles in the COVID-19 vaccination process, including limited resources for emergency response and a lack of viable pricing strategies to enable inexpensive and fair access to the urgently required vaccines. ¹⁴ These issues have made it exceedingly difficult to address the COVID-19 crisis effectively. To effectively prepare for Disease X, a thorough and global approach is necessary due to its uncertain and unpredictable nature. In order to establish a robust defense against the peril of Disease X, an imminent threat that transcends geographical limitations and disregards national boundaries, it is imperative that awareness, surveillance, healthcare infrastructure, research, and development are closely interconnected. It is imperative for the world to draw lessons from the errors and deficiencies of the past pandemic and provide the necessary infrastructure for the prompt development of vaccines and other drugs. This will expedite the attainment of herd immunity and effectively prevent future outbreaks of Disease X.

Inadequate vaccination is a significant factor impeding the development of herd immunity within a community. While vaccination hesitancy could potentially pose the most significant barrier to achieving herd immunity in low, middle, and high-income countries, our primary focus is on the LMICs due to their inadequate healthcare infrastructure. Vaccine reluctance has been included by the WHO as one of the top 10 global health threats, even prior to the emergence of the COVID-19 pandemic. ¹⁵ Typically, LMICs demonstrate a greater inclination to embrace vaccinations compared to countries with higher incomes. ¹⁶ Various studies have reported varying levels of reluctance to get vaccines in different LMICs, including India, Indonesia, Pakistan, and Burkina Faso. A survey conducted among healthcare personnel in Bangladesh revealed that over 50% of participants expressed reluctance to receive the COVID-19 vaccine, and another study revealed 38% vaccine reluctance in Pakistan. Vaccine reluctance in LMICs can be attributed to factors such as limited understanding, insufficient distribution of effective vaccines, past unfavorable encounters with foreign entities, cultural and religious convictions, and a lack of confidence in government authorities.^17,18 Vaccine acceptance is essential for acquiring herd immunity against potential Disease X. However, vaccine hesitancy poses a significant obstacle to accomplishing this goal, especially in LMICs. There is a prevalent lack of confidence and dissemination of false information surrounding the COVID-19 vaccine throughout the global public, including Austria. Approximately 10% of the population in Spain remained unvaccinated. This has the potential to impede attempts to respond to the pandemic and emphasizes the necessity for a deeper comprehension of individuals who manifest specific reluctance toward getting vaccinated. ¹⁹ Hence, it is crucial for the government and various regions to strengthen the surveillance of vaccine safety to avert the occurrence of widespread negative consequences subsequent to vaccination while also building public confidence in getting vaccinated.

The necessity of achieving herd immunity becomes paramount in light of the recurring waves of Disease X such as COVID-19 infections. Effectively and promptly spreading information about the protective benefits of vaccination can educate the public about the effectiveness of COVID-19 vaccines for both personal protection and the promotion of the greater good, emphasizing the importance of prevention over treatment and reducing the impact of this pandemic. An effective strategy to address vaccine hesitancy is to adopt a multisectoral approach, which entails intentional cooperation among different stakeholders, including the government, private corporations, religious groups, and other agencies, in order to accomplish a desired policy goal. The approach of including several sectors (health, environment, and economy) will facilitate the utilization of information, experience, and resources necessary for establishing enduring public confidence in vaccinations. ²⁰ Attaining herd immunity requires the implementation of prompt communication techniques that prioritize responsibility and the restoration of trust within healthcare authorities. ²¹ To further address any potential future endemic scenario involving Disease X, a nationwide molecular-epidemiological database could be a good choice.

Swift acquisition of herd immunity is crucial for effectively addressing infectious pandemic situations. Hence, it is fundamental to possess robust research and development capacities in order to accelerate vaccine production. In addition, meticulous planning and implementation are essential to guarantee equitable distribution of vaccines across high-, middle-, and low-income countries. In summary, it is imperative that we derive lessons from our past errors and make comprehensive preparations, encompassing research and development, public awareness, and management systems, among other aspects. This strategy will expedite the achievement of herd immunity among the population, ultimately allowing for efficient management of the forthcoming pandemic caused by Disease X.