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.
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 to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future.
The smallpox vaccine is the first vaccine to have been developed against a contagious disease. In 1796, British physician Edward Jenner demonstrated that an infection with the relatively mild cowpox virus conferred immunity against the deadly smallpox virus. Cowpox served as a natural vaccine until the modern smallpox vaccine emerged in the 20th century. From 1958 to 1977, the World Health Organization (WHO) conducted a global vaccination campaign that eradicated smallpox, making it the only human disease to be eradicated. Although routine smallpox vaccination is no longer performed on the general public, the vaccine is still being produced to guard against bioterrorism, biological warfare, and mpox.
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.
Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an infectious agent.
Vaccinia virus is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, which encodes approximately 250 genes. The dimensions of the virion are roughly 360 × 270 × 250 nm, with a mass of approximately 5–10 fg. The vaccinia virus is the source of the modern smallpox vaccine, which the World Health Organization (WHO) used to eradicate smallpox in a global vaccination campaign in 1958–1977. Although smallpox no longer exists in the wild, vaccinia virus is still studied widely by scientists as a tool for gene therapy and genetic engineering.
Indiana vesiculovirus, formerly Vesicular stomatitis Indiana virus is a virus in the family Rhabdoviridae; the well-known Rabies lyssavirus belongs to the same family. VSIV can infect insects, cattle, horses and pigs. It has particular importance to farmers in certain regions of the world where it infects cattle. This is because its clinical presentation is identical to the very important foot and mouth disease virus.
Meningococcal disease describes infections caused by the bacterium Neisseria meningitidis. It has a high mortality rate if untreated but is vaccine-preventable. While best known as a cause of meningitis, it can also result in sepsis, which is an even more damaging and dangerous condition. Meningitis and meningococcemia are major causes of illness, death, and disability in both developed and under-developed countries.
Varicella vaccine, also known as chickenpox vaccine, is a vaccine that protects against chickenpox. One dose of vaccine prevents 95% of moderate disease and 100% of severe disease. Two doses of vaccine are more effective than one. If given to those who are not immune within five days of exposure to chickenpox it prevents most cases of disease. Vaccinating a large portion of the population also protects those who are not vaccinated. It is given by injection just under the skin. Another vaccine, known as zoster vaccine, is used to prevent diseases caused by the same virus – the varicella zoster virus.
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.
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.
The rabies vaccine is a vaccine used to prevent rabies. There are several rabies vaccines available that are both safe and effective. They can be used to prevent rabies before, and, for a period of time, after exposure to the rabies virus, which is commonly caused by a dog bite or a bat bite.
Cocooning, also known as the Cocoon Strategy, is a vaccination strategy to protect infants and other vulnerable individuals from infectious diseases by vaccinating those in close contact with them. If the people most likely to transmit an infection are immune, their immunity creates a "cocoon" of protection around the newborn.
Recombinant vesicular stomatitis virus–Zaire Ebola virus (rVSV-ZEBOV), also known as Ebola Zaire vaccine live and sold under the brand name Ervebo, is an Ebola vaccine for adults that prevents Ebola caused by the Zaire ebolavirus. When used in ring vaccination, rVSV-ZEBOV has shown a high level of protection. Around half the people given the vaccine have mild to moderate adverse effects that include headache, fatigue, and muscle pain.
Ebola vaccines are vaccines either approved or in development to prevent Ebola. As of 2022, there are only vaccines against the Zaire ebolavirus. The first vaccine to be approved in the United States was rVSV-ZEBOV in December 2019. It had been used extensively in the Kivu Ebola epidemic under a compassionate use protocol. During the early 21st century, several vaccine candidates displayed efficacy to protect nonhuman primates against lethal infection.
Targeted immunization strategies are approaches designed to increase the immunization level of populations and decrease the chances of epidemic outbreaks. Though often in regards to use in healthcare practices and the administration of vaccines to prevent biological epidemic outbreaks, these strategies refer in general to immunization schemes in complex networks, biological, social or artificial in nature. 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.
The 2018 Équateur province Ebola outbreak occurred in the north-west of the Democratic Republic of the Congo (DRC) from May to July 2018. It was contained entirely within Équateur province, and was the first time that vaccination with the rVSV-ZEBOV Ebola vaccine had been attempted in the early stages of an Ebola outbreak, with a total of 3,481 people vaccinated. It was the ninth recorded Ebola outbreak in the DRC.
The Kivu Ebola epidemic was an outbreak of Ebola virus disease (EVD) mainly in eastern Democratic Republic of the Congo (DRC), and in other parts of Central Africa, from 2018 to 2020. Between 1 August 2018 and 25 June 2020 it resulted in 3,470 reported cases. The Kivu outbreak also affected Ituri Province, whose first case was confirmed on 13 August 2018. In November 2018, the outbreak became the biggest Ebola outbreak in the DRC's history, and had become the second-largest Ebola outbreak in recorded history worldwide, behind only the 2013–2016 Western Africa epidemic. In June 2019, the virus reached Uganda, having infected a 5-year-old Congolese boy who entered Uganda with his family, but was contained.
Natalie E. Dean is an American biostatistician specializing in infectious disease epidemiology. Dean is currently an assistant professor of Biostatistics at the University of Florida. Her research involves epidemiological modeling of outbreaks, including Ebola, Zika and COVID-19.
A viral vector vaccine is a vaccine that uses a viral vector to deliver genetic material (DNA) that can be transcribed by the recipient's host cells as mRNA coding for a desired protein, or antigen, to elicit an immune response. As of April 2021, six viral vector vaccines, four COVID-19 vaccines and two Ebola vaccines, have been authorized for use in humans.
