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Noroviruses are a genus of non-enveloped, single-stranded RNA viruses in the family Caliciviridae. The positive-sense RNA genome is approximately 7500 nucleotides long. Known noroviruses fall into five different genogroups (GI–GV); three groups infect humans, the other two mice, and cattle and other bovines. All are considered strains of a single species, Norwalk virus.

Noroviruses are extremely contagious, with fewer than 20 virus particles being infectious. They are transmitted directly from person to person and indirectly via contaminated water and food. After infection, the virus replicates in the small intestine, causing acute gastroenteritis, which develops 12–48 hours after exposure and lasts for 24–72 hours. The characteristic symptoms include nausea, forceful vomiting, watery diarrhoea and abdominal pain. Infection is usually self-limiting and rarely severe. Noroviruses cause 18% of acute gastroenteritis episodes in humans, with around 685 million cases and 200,000 deaths every year, mainly in very young, elderly or immunosuppressed people. No vaccine is available. Hand washing with soap and water is effective in reducing transmission.

• ...that a COVID-19 outbreak at the White House (event pictured) infected at least 35 people, including the President, First Lady, three senators, and a governor?
• ...that Alasdair Geddes worked on the WHO's smallpox-eradication programme in Bangladesh five years before diagnosing the world's last fatal case of smallpox in Birmingham, England?
• ...that an HPV prevention group focuses on preventing cervical cancer by promoting the sharing of information on cervical screening and HPV vaccination?
• ...that in a 1902 U.S. Supreme Court case, a ship owner alleged that the real purpose of Louisiana's quarantine laws was to keep Italian immigrants out of New Orleans?
• ...that Melahat Okuyan, a Turkish female microbiologist and AIDS activist, once proposed the establishment of male brothels for homosexuals and cross-dressers in order to improve public health?

Walter Reed (13 September 1851 – 22 November 1902) was an American physician in the U.S. Army medical corps who is known for his research on the epidemiology of yellow fever, at a time when viruses had only just been discovered.

Reed started to study yellow fever in the USA in the 1890s, showing that walking through swampy woods at night was associated with the disease, while drinking water from the Potomac River was not. In 1900, he led an army commission under the direction of George Miller Sternberg to investigate yellow fever in Cuba, where the disease was endemic. Building on Carlos Finlay's work suggesting that yellow fever was transmitted by a particular species of mosquito acting as a vector, Reed and co-workers confirmed Finlay's results, and also disproved the popular idea that the disease was transmitted by contaminated objects, such as clothing or bedding. The experiments involved the deliberate infection of human volunteers, several of whom died of yellow fever, and Reed pioneered the concept of medical consent.

May 1955: First issue of Virology; first English-language journal dedicated to virology

4 May 1984: HTLV-III, later HIV, identified as the cause of AIDS by Robert Gallo and coworkers

5 May 1939: First electron micrographs of tobacco mosaic virus taken by Helmut Ruska and coworkers

5 May 1983: Structure of influenza neuraminidase solved by Jose Varghese, Graeme Laver and Peter Colman

8 May 1980: WHO announced formally the global eradication of smallpox

11 May 1978: SV40 sequenced by Walter Fiers and coworkers

12 May 1972: Gene for bacteriophage MS2 coat protein is sequenced by Walter Fiers and coworkers, the first gene to be completely sequenced

13 May 2011: Boceprevir approved for the treatment of chronic hepatitis C virus (HCV) infection, the first direct-acting antiviral for HCV

14 May 1796: Edward Jenner inoculated James Phipps (pictured) with cowpox

15/16 May 1969: Death of Robert Rayford, the earliest confirmed case of AIDS outside Africa

18 May 1998: First World AIDS Vaccine Day

20 May 1983: Isolation of the retrovirus LAV, later HIV, by Luc Montagnier, Françoise Barré-Sinoussi and coworkers

23 May 2011: Telaprevir approved for the treatment of chronic HCV infection

25 May 2011: WHO declared rinderpest eradicated

31 May 1937: First results in humans from the 17D vaccine for yellow fever published by Max Theiler and Hugh H. Smith

The MMR vaccine and autism fraud refers to the false claim that the combined vaccine for measles, mumps and rubella (MMR) might be associated with colitis and autism spectrum disorders. Multiple large epidemiological studies have since found no link between the vaccine and autism. The notion originated in a fraudulent research paper by Andrew Wakefield and co-authors, published in the prestigious medical journal The Lancet in 1998. Sunday Times journalist Brian Deer's investigations revealed that Wakefield had manipulated evidence and had multiple undeclared conflicts of interest. The paper was retracted in 2010, when the Lancet's editor-in-chief Richard Horton characterised it as "utterly false". Wakefield was found guilty of serious professional misconduct by the General Medical Council, and struck off the UK's Medical Register. The claims in Wakefield's article were widely reported in the press, resulting in a sharp drop in vaccination uptake in the UK and Ireland. A greatly increased incidence of measles and mumps followed, leading to deaths and serious permanent injuries.

Subcategories of virology: