Targeted immunization strategies

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Targeted immunization strategies are approaches designed to increase the immunization level of populations and decrease the chances of epidemic outbreaks. [1] Though often in regards to use in healthcare practices and the administration of vaccines to prevent biological epidemic outbreaks, [2] these strategies refer in general to immunization schemes in complex networks, biological, social or artificial in nature. [1] Identification of at-risk groups and individuals with higher odds of spreading the disease often plays an important role in these strategies, since targeted immunization in high-risk groups is necessary for effective eradication efforts and has a higher return on investment than immunizing larger but lower-risk groups. [1] [3] [4]

Contents

Background

The success of vaccines in preventing major outbreaks relies on the mechanism of herd immunity, also known as community immunity, where the immunization of individuals provides protection for not only the individuals, but also the community at large. [5] In cases of biological contagions such as influenza, measles, and chicken pox, immunizing a critical community size can provide protection against the disease for members who cannot be vaccinated themselves (infants, pregnant women, and immunocompromised individuals). Often however these vaccine programmes require the immunization of a large majority of the population to provide herd immunity. [6] A few successful vaccine programmes have led to the eradication of infectious diseases like small pox [7] and rinderpest, and the near eradication of polio, [8] which plagued the world before the second half of the 20th century. [9] [10]

Network-based strategies

More recently researchers have looked at exploiting network connectivity properties to better understand and design immunization strategies to prevent major epidemic outbreaks. [11] Many real networks like the Internet, World Wide Web, and even sexual contact networks [12] have been shown to be scale-free networks and as such exhibit a power-law distribution for the degree distribution. In large networks this results in the vast majority of nodes (individuals in social networks) having few connections or low degree k, while a few "hubs" have many more connections than the average <k>. [13] This wide variability (heterogeneity) in degree offers immunization strategies based on targeting members of the network according to their connectivity rather than random immunization of the network. In epidemic modeling on scale-free networks, targeted immunization schemes can considerably lower the vulnerability of a network to epidemic outbreaks over random immunization schemes. Typically these strategies result in the need for far fewer nodes to be immunized in order to provide the same level of protection to the entire network as in random immunization. [1] [14] In circumstances where vaccines are scarce, efficient immunization strategies become necessary to preventing infectious outbreaks. [15]

Examples

A common approach for targeted immunization studies in scale-free networks focuses on targeting the highest degree nodes for immunization. These nodes are the most highly connected in the network, making them more likely to spread the contagion if infected. Immunizing this segment of the network can drastically reduce the impact of the disease on the network and requires the immunization of far fewer nodes compared to randomly selecting nodes. [1] However, this strategy relies on knowing the global structure of the network, which may not always be practical.[ citation needed ]

A recent centrality measure, Percolation Centrality, introduced by Piraveenan et al. [16] is particularly useful in identifying nodes for vaccination based on the network topology. Unlike node degree which depends on topology alone, however, percolation centrality takes into account the topological importance of a node as well as its distance from infected nodes in deciding its overall importance. Piraveenan et al. [16] has shown that percolation centrality-based vaccination is particularly effective when the proportion of people already infected is on the same order of magnitude as the number of people who could be vaccinated before the disease spreads much further. If infection spread is at its infancy, then ring-vaccination surrounding the source of infection is most effective, whereas if the proportion of people already infected is much higher than the number of people that could be vaccinated quickly, then vaccination will only help those who are vaccinated and herd immunity cannot be achieved. [6] Percolation centrality-based vaccination is most effective in the critical scenario where the infection has already spread too far to be completely surrounded by ring-vaccination, yet not spread wide enough so that it cannot be contained by strategic vaccination. Nevertheless, Percolation Centrality also needs full network topology to be computed, and thus is more useful in higher levels of abstraction (for example, networks of townships rather than social networks of individuals), where the corresponding network topology can more readily be obtained.[ citation needed ]

Increasing immunization coverage

Millions of children worldwide do not receive all of the routine vaccinations as per their national schedule. As immunization is a powerful public health strategy for improving child survival, it is important to determine what strategies work best to increase coverage. A Cochrane review assessed the effectiveness of intervention strategies to boost and sustain high childhood immunization coverage in low- and middle-income countries. [17] Forty-one trials were included but most of the evidence was of low quality. [17] Providing parents and other community members with information on immunization, health education at facilities in combination with redesigned immunization reminder cards, regular immunization outreach with and without household incentives, home visits, and integration of immunization with other services may improve childhood immunization coverage in low-and middle-income countries. [17]

See also

Related Research Articles

<span class="mw-page-title-main">Polio</span> Infectious disease caused by poliovirus

Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 75% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe symptoms develop such as headache, neck stiffness, and paresthesia. These symptoms usually pass within one or two weeks. A less common symptom is permanent paralysis, and possible death in extreme cases. Years after recovery, post-polio syndrome may occur, with a slow development of muscle weakness similar to that which the person had during the initial infection.

<span class="mw-page-title-main">Vaccination</span> Administration of a vaccine to protect against disease

Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating the body's adaptive immunity, they help prevent sickness from an infectious disease. When a sufficiently large percentage of a population has been vaccinated, herd immunity results. Herd immunity protects those who may be immunocompromised and cannot get a vaccine because even a weakened version would harm them. The effectiveness of vaccination has been widely studied and verified. Vaccination is the most effective method of preventing infectious diseases; widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the elimination of diseases such as polio and tetanus from much of the world. However, some diseases, such as measles outbreaks in America, have seen rising cases due to relatively low vaccination rates in the 2010s – attributed, in part, to vaccine hesitancy. According to the World Health Organization, vaccination prevents 3.5–5 million deaths per year.

<span class="mw-page-title-main">Vaccine</span> Pathogen-derived preparation that provides acquired immunity to an infectious disease

A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and recognize further and destroy any of the microorganisms associated with that agent that it may encounter in the future.

<span class="mw-page-title-main">Herd immunity</span> Concept in epidemiology

Herd immunity is a form of indirect protection that applies only to contagious diseases. It occurs when a sufficient percentage of a population has become immune to an infection, whether through previous infections or vaccination, thereby reducing the likelihood of infection for individuals who lack immunity.

<span class="mw-page-title-main">Polio vaccine</span> Vaccine to prevent poliomyelitis

Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated poliovirus given by injection (IPV) and a weakened poliovirus given by mouth (OPV). The World Health Organization (WHO) recommends all children be fully vaccinated against polio. The two vaccines have eliminated polio from most of the world, and reduced the number of cases reported each year from an estimated 350,000 in 1988 to 33 in 2018.

<span class="mw-page-title-main">Immunization</span> Process by which an individuals immune system becomes fortified against an infectious agent

Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an infectious agent.

<span class="mw-page-title-main">Basic reproduction number</span> Metric in epidemiology

In epidemiology, the basic reproduction number, or basic reproductive number, denoted , of an infection is the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection. The definition assumes that no other individuals are infected or immunized. Some definitions, such as that of the Australian Department of Health, add the absence of "any deliberate intervention in disease transmission". The basic reproduction number is not necessarily the same as the effective reproduction number , which is the number of cases generated in the current state of a population, which does not have to be the uninfected state. is a dimensionless number and not a time rate, which would have units of time−1, or units of time like doubling time.

Mathematical models can project how infectious diseases progress to show the likely outcome of an epidemic and help inform public health and plant health interventions. Models use basic assumptions or collected statistics along with mathematics to find parameters for various infectious diseases and use those parameters to calculate the effects of different interventions, like mass vaccination programs. The modelling can help decide which intervention(s) to avoid and which to trial, or can predict future growth patterns, etc.

<span class="mw-page-title-main">Pulse Polio</span> Indian governmental immunisation campaign

Pulse Polio is an immunisation campaign established by the government of India to eliminate poliomyelitis (polio) in India by vaccinating all children under the age of five years against the polio virus. The project fights polio through a large-scale, pulse vaccination programme and monitoring for poliomyelitis cases.

<span class="mw-page-title-main">Vaccine hesitancy</span> Reluctance or refusal to be vaccinated or have ones children vaccinated

Vaccine hesitancy is a delay in acceptance, or refusal, of vaccines despite the availability of vaccine services and supporting evidence. The term covers refusals to vaccinate, delaying vaccines, accepting vaccines but remaining uncertain about their use, or using certain vaccines but not others. The scientific consensus that vaccines are generally safe and effective is overwhelming. Vaccine hesitancy often results in disease outbreaks and deaths from vaccine-preventable diseases. Therefore, the World Health Organization characterizes vaccine hesitancy as one of the top ten global health threats.

<span class="mw-page-title-main">Polio eradication</span> Effort to permanently eliminate all cases of poliomyelitis infection

Polio eradication, the permanent global cessation of circulation of the poliovirus and hence elimination of the poliomyelitis (polio) it causes, is the aim of a multinational public health effort begun in 1988, led by the World Health Organization (WHO), the United Nations Children's Fund (UNICEF) and the Rotary Foundation. These organizations, along with the U.S. Centers for Disease Control and Prevention (CDC) and The Gates Foundation, have spearheaded the campaign through the Global Polio Eradication Initiative (GPEI). Successful eradication of infectious diseases has been achieved twice before, with smallpox in humans and rinderpest in ruminants.

A vaccination policy is a health policy adopted in order to prevent the spread of infectious disease. These policies are generally put into place by state or local governments, but may also be set by private facilities, such as workplaces or schools. Many policies have been developed and implemented since vaccines were first made widely available.

Mass vaccination is a public policy effort to vaccinate a large number of people, possibly the entire population of the world or of a country or region, within a short period of time. This policy may be directed during a pandemic, when there is a localized outbreak or scare of a disease for which a vaccine exists, or when a new vaccine is invented.

Vaccinate Your Family (VYF), formerly known as Every Child By Two (ECBT), is a non-profit organization, based in the United States, which advocates for vaccinations. Founded in 1991, its stated goals are to "raise awareness of the critical need for timely immunizations and to foster a systematic way to immunize all of America's children by age two." ECBT was founded by former First Lady of the United States Rosalynn Carter and former First Lady of Arkansas Betty Bumpers. ECBT was renamed to Vaccinate Your Family in 2018.

Pakistan is one of the two remaining countries in the world where poliomyelitis (polio) is still categorized as an endemic viral infection, the other one being Afghanistan. While it has yet to fully eradicate Polio, there has been a downwards trend in the number of reported cases per year; the total count of wild poliovirus cases in Pakistan in 2019 was 147, compared to 84 in 2020, 1 in 2021, 20 in 2022, 6 in 2023 and 2 to date in 2024.

<span class="mw-page-title-main">Vaccine-naive</span> Resistance of vaccination

Vaccine-naive is a lack of immunity, or immunologic memory, to a disease because the person has not been vaccinated. There are a variety of reasons why a person may not have received a vaccination, including contraindications due to preexisting medical conditions, lack of resources, previous vaccination failure, religious beliefs, personal beliefs, fear of side-effects, phobias to needles, lack of information, vaccine shortages, physician knowledge and beliefs, social pressure, and natural resistance.

<span class="mw-page-title-main">Pulse vaccination strategy</span> Method to eradicate an epidemic by repeatedly vaccinating a group at risk

The pulse vaccination strategy is a method used to eradicate an epidemic by repeatedly vaccinating a group at risk, over a defined age range, until the spread of the pathogen has been stopped. It is most commonly used during measles and polio epidemics to quickly stop the spread and contain the outbreak.

<span class="mw-page-title-main">Ring vaccination</span> Strategy to inhibit the spread of a disease by vaccinating those most likely to be infected

Ring vaccination is a strategy to inhibit the spread of a disease by vaccinating those who are most likely to be infected.

<span class="mw-page-title-main">Vaccination policy of the United States</span> Overview of the vaccination policy in the United States of America

Vaccination policy of the United States is the subset of U.S. federal health policy that deals with immunization against infectious disease. It is decided at various levels of the government, including the individual states. This policy has been developed over the approximately two centuries since the invention of vaccination with the purpose of eradicating disease from the U.S. population, or creating a herd immunity. Policies intended to encourage vaccination impact numerous areas of law, including regulation of vaccine safety, funding of vaccination programs, vaccine mandates, adverse event reporting requirements, and compensation for injuries asserted to be associated with vaccination.

Misinformation related to immunization and the use of vaccines circulates in mass media and social media in spite of the fact that there is no serious hesitancy or debate within mainstream medical and scientific circles about the benefits of vaccination. Unsubstantiated safety concerns related to vaccines are often presented on the internet as being scientific information. A high proportion of internet sources on the topic are "inaccurate on the whole" which can lead people searching for information to form "significant misconceptions about vaccines".

References

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