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An epidemic is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.
Influenza vaccines, colloquially known as flu shots or the flu jab, are vaccines that protect against infection by influenza viruses. New versions of the vaccines are developed twice a year, as the influenza virus rapidly changes. While their effectiveness varies from year to year, most provide modest to high protection against influenza. Vaccination against influenza began in the 1930s, with large-scale availability in the United States beginning in 1945.
Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.
Flu season is an annually recurring time period characterized by the prevalence of an outbreak of influenza (flu). The season occurs during the cold half of the year in each hemisphere. It takes approximately two days to show symptoms. Influenza activity can sometimes be predicted and even tracked geographically. While the beginning of major flu activity in each season varies by location, in any specific location these minor epidemics usually take about three weeks to reach its pinnacle, and another three weeks to significantly diminish.
Influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus (IAV). Some human-adapted strains of H1N1 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs and in birds. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein.
An influenza pandemic is an epidemic of an influenza virus that spreads across a large region and infects a large proportion of the population. There have been five major influenza pandemics in the last 140 years, with the 1918 flu pandemic being the most severe; this is estimated to have been responsible for the deaths of 50–100 million people. The 2009 swine flu pandemic resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
Michael Thomas Osterholm is an American epidemiologist, Regents Professor at the University of Minnesota School of Public Health, and director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
Disease surveillance is an epidemiological practice by which the spread of disease is monitored in order to establish patterns of progression. The main role of disease surveillance is to predict, observe, and minimize the harm caused by outbreak, epidemic, and pandemic situations, as well as increase knowledge about which factors contribute to such circumstances. A key part of modern disease surveillance is the practice of disease case reporting.
The pandemic severity index (PSI) was a proposed classification scale for reporting the severity of influenza pandemics in the United States. The PSI was accompanied by a set of guidelines intended to help communicate appropriate actions for communities to follow in potential pandemic situations. Released by the United States Department of Health and Human Services (HHS) on February 1, 2007, the PSI was designed to resemble the Saffir-Simpson Hurricane Scale classification scheme. The index was replaced by the Pandemic Severity Assessment Framework in 2014, which uses quadrants based on transmissibility and clinical severity rather than a linear scale.
Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
The 2009 swine flu pandemic, caused by the H1N1/swine flu/influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, was the third recent flu pandemic involving the H1N1 virus. The first identified human case was in La Gloria, Mexico, a rural town in Veracruz. The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to the term "swine flu".
The 2009 flu pandemic in the United States was caused by a novel strain of the Influenza A/H1N1 virus, commonly referred to as "swine flu", that was first detected on 15 April 2009. While the 2009 H1N1 virus strain was commonly referred to as "swine flu", there is no evidence that it is endemic to pigs or of transmission from pigs to people; instead, the virus spreads from person to person. On April 25, the World Health Organization declared a public health emergency, followed concurringly by the Obama administration on April 26.
In 1976, an outbreak of the swine flu, influenza A virus subtype H1N1 at Fort Dix, New Jersey caused one death, hospitalized 13, and led to a mass immunization program. After the program began, the vaccine was associated with an increase in reports of Guillain–Barré syndrome (GBS), which can cause paralysis, respiratory arrest, and death. The immunization program was ended after approximately 43 million United States citizens had been administered the vaccine.
The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media due to the prevailing belief that it originated in pigs. The virus is believed to have originated around September 2008 in central Mexico.
Influenza prevention involves taking steps that one can use to decrease their chances of contracting flu viruses, such as the Pandemic H1N1/09 virus, responsible for the 2009 flu pandemic.
H5N6 is a subtype of the species Influenza A virus. Infected birds shed the virus in their saliva, mucus, and feces. The virus was first detected in poultry in 2013, since then spreading among wild bird populations and poultry around the world. Humans can be infected through unprotected contact with infected birds or contaminated surfaces. The virus transmits by getting into a person's eyes, nose, mouth, and through inhalation. Human infections are rare. Since 2014, at least 94 cases have occurred in humans. 37 people have died. A spike in human cases was reported in 2021. There have been no confirmed cases of human-to-human transmission. Some infections have been identified where no direct contact with infected birds or contaminated surfaces has been known to had occurred. Only one infected woman has said that she never came into any contact with poultry.
The 1957–1958 Asian flu pandemic was a global pandemic of influenza A virus subtype H2N2 that originated in Guizhou in Southern China. The number of excess deaths caused by the pandemic is estimated to be 1–4 million around the world, making it one of the deadliest pandemics in history. A decade later, a reassorted viral strain H3N2 further caused the Hong Kong flu pandemic (1968–1969).
The Pandemic Severity Assessment Framework (PSAF) is an evaluation framework published by the Centers for Disease Control and Prevention in 2016 which uses quadrants to evaluate both the transmissibility and clinical severity of an influenza pandemic and to combine these into an overall impact estimate. Clinical severity is calculated via multiple measures including case fatality rate, case-hospitalization ratios, and deaths-hospitalizations ratios, while viral transmissibility is measured via available data among secondary household attack rates, school attack rates, workplace attack rates, community attack rates, rates of emergency department and outpatient visits for influenza-like illness.
Helen Y. Chu is an American immunologist who is an assistant professor of medicine at the University of Washington. Her research considers maternal immunization, with a focus on influenza and respiratory syncytial virus. During the COVID-19 pandemic, Chu was the first physician to recognise community transmission of the coronavirus disease within the United States.
Type A influenza vaccine is for the prevention of infection of influenza A virus and also the influenza-related complications. Different monovalent type A influenza vaccines have been developed for different subtypes of influenza A virus including H1N1 and H5N1. Both intramuscular injection or intranasal spray are available on market. Unlike the seasonal influenza vaccines which are used annually, they are usually used during the outbreak of certain strand of subtypes of influenza A. Common adverse effects includes injection site reaction and local tenderness. Incidences of headache and myalgia were also reported with H1N1 whereas cases of fever has also been demonstrated with H5N1 vaccines. It is stated that immunosuppressant therapies would reduce the therapeutic effects of vaccines and that people with egg allergy should go for the egg-free preparations.
References
- ↑ "Lyn Finelli | Longdom Publishing SL | 111934". www.longdom.org. Retrieved 2023-12-19.
- ↑ Sapatkin, Don (2012-12-19). "Cough-and-cold season arrives suddenly, hits hard". The Philadelphia Inquirer . Retrieved 2023-12-19.
- ↑ "Lyn Finelli, Chief of Surveillance and Outbreak Response, Influenza Division, National Center for Immunization and Respiratory Diseases". isirv.org. Retrieved 2023-12-19.
- ↑ "Novel H3N2 swine flu viruses infected 2 children, CDC says | CIDRAP". www.cidrap.umn.edu. 2011-09-02. Retrieved 2023-12-19.
- ↑ "1 Million Americans May Have H1N1 Flu - CBS News". CBS News . 2009-06-25. Retrieved 2023-12-19.
- ↑ Allday, Erin (2014-01-29). "H1N1 flu strain has returned with a vengeance". SFGATE. Retrieved 2023-12-19.
- ↑ Sun, Lena H. (2023-05-17). "Second wave of flu blows in with spring; Northeast states hardest hit by influenza B". The Washington Post . ISSN 0190-8286 . Retrieved 2023-12-19.
- ↑ Burling, Stacey (2021-04-08). "Merck study finds survival rates among hospitalized COVID-19 patients rose after early months". The Philadelphia Inquirer . Retrieved 2023-12-19.
- ↑ "COVID hospital death rates fall, but impact still high | CIDRAP". www.cidrap.umn.edu. 2021-04-16. Retrieved 2023-12-19.
- ↑ Lipsitch, Marc; Swerdlow, David L.; Finelli, Lyn (2020-03-26). "Defining the Epidemiology of Covid-19 — Studies Needed". New England Journal of Medicine. 382 (13): 1194–1196. doi: 10.1056/NEJMp2002125 . ISSN 0028-4793. PMID 32074416.
- ↑ "Lyn Finelli, Chief of Surveillance and Outbreak Response, Influenza Division, National Center for Immunization and Respiratory Diseases". isirv.org. Retrieved 2023-12-19.
