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The 2009 flu pandemic or swine flu was an influenza pandemic that lasted from January 2009 to August 2010, and the second of the two pandemics involving H1N1 influenza virus (the first being the 1918–1920 Spanish flu pandemic), albeit a new strain. First described in April 2009, the virus appeared to be a new strain of H1N1, which resulted from a previous triple reassortment of bird, swine, and human flu viruses further combined with a Eurasian pig flu virus, leading to the term "swine flu". According to WHO, the laboratory confirmed death toll is more than 18,036. Meanwhile, some studies estimated that 11 to 21 percent of the global population at the time – or around 700 million to 1.4 billion people (out of a total of 6.8 billion) – contracted the illness. This was more than the number of people infected by the Spanish flu pandemic, but only resulted in about 150,000 to 575,000 fatalities for the 2009 pandemic. A follow-up study done in September 2010 showed that the risk of serious illness resulting from the 2009 H1N1 flu was no higher than that of the yearly seasonal flu. For comparison, the WHO estimates that 250,000 to 500,000 people die of seasonal flu annually.

Unlike most strains of influenza, the Pandemic H1N1/09 virus does not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1 pandemic. Even in the case of previously very healthy people, a small percentage develop pneumonia or acute respiratory distress syndrome (ARDS). This manifests itself as increased breathing difficulty and typically occurs three to six days after initial onset of flu symptoms. The pneumonia caused by flu can be either direct viral pneumonia or a secondary bacterial pneumonia. A November 2009 New England Journal of Medicine article recommended that flu patients whose chest X-ray indicates pneumonia receive both antivirals and antibiotics. In particular, it is a warning sign if a child (and presumably an adult) seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia.

The 2009 flu pandemic in the United States was a novel strain of the Influenza A/H1N1 virus, commonly referred to as "swine flu", that began in the spring of 2009. The virus had spread to the US from an outbreak in Mexico.

The U.S. Centers for Disease Control and Prevention (CDC) estimates that from April 12, 2009 to April 10, 2010, there were 60.8 million cases, 274,000 hospitalizations, and 12,469 deaths (0.02% infection fatality rate/Mortality rate) in the United States due to the virus.

The 2019–20 coronavirus pandemic is an ongoing pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The outbreak was first identified in Wuhan, Hubei, China, in December 2019, and was recognized as a pandemic by the World Health Organization (WHO) on 11 March. As of 28 March 2020, more than 663,000 cases of COVID-19 have been reported in over 190 countries and territories, resulting in approximately 30,800 deaths. More than 141,000 people have since recovered.

The virus is mainly spread during close contact and via respiratory droplets produced when people cough or sneeze. Respiratory droplets may be produced during breathing but the virus is not considered airborne. People may also catch COVID-19 by touching a contaminated surface and then their face. It is most contagious when people are symptomatic, although spread may be possible before symptoms appear. The time between exposure and symptom onset is typically around five days, but may range from 2 to 14 days. Common symptoms include fever, cough, and shortness of breath. Complications may include pneumonia and acute respiratory distress syndrome. There is no known vaccine or specific antiviral treatment. Primary treatment is symptomatic and supportive therapy. Recommended preventive measures include hand washing, covering one's mouth when coughing, maintaining distance from other people, and monitoring and self-isolation for people who suspect they are infected.

Efforts to prevent the virus spreading include travel restrictions, quarantines, curfews, workplace hazard controls, event postponements and cancellations, and facility closures. These include the quarantine of Hubei, national or regional quarantines elsewhere in the world, curfew measures in China and South Korea, various border closures or incoming passenger restrictions, screening at airports and train stations, and outgoing passenger travel bans. Schools and universities have closed either on a nationwide or local basis in more than 160 countries, affecting more than 1.5 billion students.

The pandemic has led to severe global socioeconomic disruption, the postponement or cancellation of sporting, religious, and cultural events, and widespread fears of supply shortages which have spurred panic buying. Misinformation and conspiracy theories about the virus have spread online, and there have been incidents of xenophobia and racism against Chinese and other East and Southeast Asian people.

HeLa (; also Hela or hela) is an immortal cell line used in scientific research. It is the oldest and most commonly used human cell line. The line was derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a patient who died of cancer on October 4, 1951. The cell line was found to be remarkably durable and prolific, which gives rise to its extensive use in scientific research.

The cells from Lacks's cancerous cervical tumor were taken without her knowledge or consent, which was common practice at the time. Cell biologist George Otto Gey found that they could be kept alive, and developed a cell line. Previously, cells cultured from other human cells would only survive for a few days. Scientists would spend more time trying to keep the cells alive than performing actual research on them. Cells from Lacks' tumor behaved differently. As was custom for Gey's lab assistant, she labeled the culture 'HeLa', the first two letters of the patient's first and last name; this became the name of the cell line.

These were the first human cells grown in a lab that were naturally "immortal", meaning that they do not die after a set number of cell divisions (i.e. cellular senescence). These cells could be used for conducting a multitude of medical experiments—if the cells died, they could simply be discarded and the experiment attempted again on fresh cells from the culture. This represented an enormous boon to medical and biological research, as previously stocks of living cells were limited and took significant effort to culture.

The stable growth of HeLa enabled a researcher at the University of Minnesota hospital to successfully grow polio virus, enabling the development of a vaccine, and by 1952, Jonas Salk developed a vaccine for polio using these cells. To test Salk's new vaccine, the cells were put into mass production in the first-ever cell production factory.

In 1953, HeLa cells were the first human cells successfully cloned and demand for the HeLa cells quickly grew in the nascent biomedical industry. Since the cells' first mass replications, they have been used by scientists in various types of investigations including disease research, gene mapping, effects of toxic substances on organisms, and radiation on humans. Additionally, HeLa cells have been used to test human sensitivity to tape, glue, cosmetics, and many other products.

Scientists have grown an estimated 50 million metric tons of HeLa cells, and there are almost 11,000 patents involving these cells.

The HeLa cell lines are also notorious for invading other cell cultures in laboratory settings. Some have estimated that HeLa cells have contaminated 10–20% of all cell lines currently in use.

This article is a list of deaths caused by an infectious disease. Widespread non-communicable diseases such as cardiovascular disease and cancer are not included.

Rabies is a viral disease that causes inflammation of the brain in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: violent movements, uncontrolled excitement, fear of water, an inability to move parts of the body, confusion, and loss of consciousness. Once symptoms appear, the result is nearly always death. The time period between contracting the disease and the start of symptoms is usually one to three months, but can vary from less than one week to more than one year. The time depends on the distance the virus must travel along peripheral nerves to reach the central nervous system.

Rabies is caused by lyssaviruses, including the rabies virus and Australian bat lyssavirus. It is spread when an infected animal bites or scratches a human or other animal. Saliva from an infected animal can also transmit rabies if the saliva comes into contact with the eyes, mouth, or nose. Globally, dogs are the most common animal involved. In countries where dogs commonly have the disease, more than 99% of rabies cases are the direct result of dog bites. In the Americas, bat bites are the most common source of rabies infections in humans, and less than 5% of cases are from dogs. Rodents are very rarely infected with rabies. The disease can be diagnosed only after the start of symptoms.

Animal control and vaccination programs have decreased the risk of rabies from dogs in a number of regions of the world. Immunizing people before they are exposed is recommended for those at high risk, including those who work with bats or who spend prolonged periods in areas of the world where rabies is common. In people who have been exposed to rabies, the rabies vaccine and sometimes rabies immunoglobulin are effective in preventing the disease if the person receives the treatment before the start of rabies symptoms. Washing bites and scratches for 15 minutes with soap and water, povidone-iodine, or detergent may reduce the number of viral particles and may be somewhat effective at preventing transmission. As of 2016, only fourteen people had survived a rabies infection after showing symptoms.

Rabies caused about 17,400 human deaths worldwide in 2015. More than 95% of human deaths from rabies occur in Africa and Asia. About 40% of deaths occur in children under the age of 15. Rabies is present in more than 150 countries and on all continents but Antarctica. More than 3 billion people live in regions of the world where rabies occurs. A number of countries, including Australia and Japan, as well as much of Western Europe, do not have rabies among dogs. Many Pacific islands do not have rabies at all. It is classified as a neglected tropical disease.

The Spanish flu (also known as the 1918 flu pandemic) was an unusually deadly influenza pandemic. Lasting from January 1918 to December 1920, it infected 500 million people—about a quarter of the world's population at the time. The death toll is estimated to have been anywhere from 17 million to 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in human history.

To maintain morale, World War I censors minimized early reports of illness and mortality in Germany, the United Kingdom, France, and the United States. Papers were free to report the epidemic's effects in neutral Spain, such as the grave illness of King Alfonso XIII, and these stories created a false impression of Spain as especially hard hit. This gave rise to the pandemic's nickname, "Spanish flu". Historical and epidemiological data are inadequate to identify with certainty the pandemic's geographic origin, with varying views as to the origin.

Most influenza outbreaks disproportionately kill the very young and the very old, with a higher survival rate for those in between, but the Spanish flu pandemic resulted in a higher than expected mortality rate for young adults. Scientists offer several possible explanations for the high mortality rate of the 1918 influenza pandemic. Some analyses have shown the virus to be particularly deadly because it triggers a cytokine storm, which ravages the stronger immune system of young adults. In contrast, a 2007 analysis of medical journals from the period of the pandemic found that the viral infection was no more aggressive than previous influenza strains. Instead, malnourishment, overcrowded medical camps and hospitals, and poor hygiene promoted bacterial superinfection. This superinfection killed most of the victims, typically after a somewhat prolonged death bed.

The Spanish flu was the first of two pandemics caused by the H1N1 influenza virus; the second was the swine flu in 2009.

Sputnik virophage (from Russian cпутник "satellite", Latin "virus" and Greek φάγειν phagein "to eat") is a subviral agent that reproduces in amoeba cells that are already infected by a certain helper virus; Sputnik uses the helper virus's machinery for reproduction and inhibits replication of the helper virus.

Viruses like Sputnik that depend on co-infection of the host cell by helper viruses are known as satellite viruses. At its discovery in a Paris water-cooling tower in 2008 Sputnik was the first known satellite virus that inhibited replication of its helper virus and thus acted as a parasite of that virus. In analogy to the term bacteriophage it was called a virophage. However, the usage of this term and the relationship between virophages and classical satellite viruses remain controversial.

Sputnik virophages were found infecting giant viruses of Mimiviridae group A. However, they are able to grow in amoebae infected by Mimiviridae of any of the groups A, B, and C.

A super-spreader is an unusually contagious organism infected with a disease. In context of a human-borne illness, a super-spreader is an individual who is more likely to infect others, compared with a typical infected person. Such super-spreaders are of particular concern in epidemiology.

Some cases of super-spreading conform to the 80/20 rule, where approximately 20% of infected individuals are responsible for 80% of transmissions, although super-spreading can still be said to occur when super-spreaders account for a higher or lower percentage of transmissions. In epidemics with super-spreading, the majority of individuals infect relatively few secondary contacts.

Super-spreading events are shaped by multiple factors including a decline in herd immunity, nosocomial infections, virulence, viral load, misdiagnosis, airflow dynamics, immune suppression, and co-infection with another pathogen.

A COVID-19 vaccine is a hypothetical vaccine against coronavirus disease 2019 (COVID‑19). Although no vaccine has completed clinical trials, there are multiple attempts in progress to develop such a vaccine. In February 2020, the World Health Organization (WHO) said it did not expect a vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative virus, to become available in less than 18 months. The Coalition for Epidemic Preparedness Innovations (CEPI) – which is organizing a US$2 billion worldwide fund for rapid investment and development of vaccine candidates – indicated in April that a vaccine may be available under emergency use protocols in less than 12 months or by early 2021. On 4 May 2020, the WHO organized a telethon to raise US$8 billion from forty countries to support rapid development of vaccines to prevent COVID-19 infections, also announcing deployment of an international "Solidarity trial" for simultaneous evaluation of several vaccine candidates reaching Phase II-III clinical trials.

By May, 159 vaccine candidates were in development, with five having been initiated in Phase I–II safety and efficacy studies in human subjects, and seven in Phase I trials.