Which influenza type is usually responsible for pandemics

About 34, people died in the United States during this pandemic. Some scientists think that a similarity with the Asian flu may have helped protect people from more serious disease. Like the Asian flu, the Hong Kong flu had an N2 component. The next significant threat to emerge in influenza came again from Asia, where an avian influenza H5N1 infected birds and then spread to humans. A number of humans became ill and died from the virus. The outbreaks were particularly severe in , when tens of millions of poultry and waterfowl died from the flu.

The virus, however, did not spread from person to person, but only among birds and then to humans. The lack of human-to-human spread limited disease incidence. After widespread destruction of poultry flocks, the threat diminished. The threat of bird flu remains, however, in that another deadly strain could arise that would be capable of spreading from human to human and causing a pandemic.

The latest pandemic influenza appeared in Mexico in mid-March This flu appeared particularly troubling at first, because death rates in Mexico seemed unusually high. Soon cases appeared in California and Texas, and the disease continued to spread.

Scientists identified the virus as influenza A H1N1, with its origin likely in pigs. The World Health Organization provided global guidance on the emerging threat, and national, state, and local governments began implementing pandemic influenza plans.

Though the disease spread rapidly, with an initial peak in the United States of early May, the resulting illness did not turn out to be as severe as the early Mexican reports indicated it might be. Still, the disease took a heavier toll on children and young adults than seasonal flu typically does. One possible explanation for this is that many people born before seemed to have some pre-existing immunity to the virus, possibly because virus types related to the H1N1 flu pandemic were still circulating earlier in the 20 th century.

A massive effort to produce vaccine for the new H1N1 strain began shortly after scientists identified the virus. The virus proved to grow slowly during the manufacturing process, which relies on cultivation of the virus in chicken eggs. In the United States, most vaccine arrived after the second peak of influenza cases in late October.

In fact, experts had predicted that million doses of the vaccine would be available by mid-October. But by that time, only 30 million doses had been delivered. Between , and , H1N1-related hospitalizations occurred during this period, as did 8,, deaths. Was H1N1 the result of antigenic shift or antigenic drift? No new H- or N-subtype entered the human population, which would indicate antigenic shift.

But neither does the virus obviously fit with the definition of antigenic drift. As one report says,. The H1N1 virus does not fit the classic definition of a new subtype for which most of the population has no previous infection experience.

Since , H1N1 viruses have been in continuous circulation, and most persons born before have previous infection experience with H1N1 strains in the pre-H2N2 era. The World Health Organization developed new pandemic guidelines in that prompted national and local authorities to revisit and upgrade their pandemic preparedness plans. The plans had been developed after the bird flu outbreaks of late s.

The H1N1 pandemic provided public health authorities a chance to implement new plans designed to respond to pandemic illness. As groups study the pandemic response, many point to the need for quicker development and distribution of influenza vaccine. Industry and public health officials are examining new technologies and methods to increase vaccine availability. For instance, U. Additionally, they might begin to use new antigen cultivation technologies to avoid the slow process of vaccine production in eggs.

The need for continued attention to pandemic influenza plans is apparent. Department of Health and Human Services. This article has been translated into Ukrainian here and French here.

Avian influenza, current situation. Avian influenza A virus infections in humans. Racaniello, V. Virology Blog. May 13, HHS pandemic influenza plan. Reid, A. Emerging Infectious Diseases. Sullivan, S. Mayo Clin Proc. Sample, I. A history of major flu pandemics. The Guardian.

March 28, Pandemic flu preparedness: Lessons from the front lines. June Influenza typically begins with the abrupt onset of symptoms following an incubation period of 1 to 2 days. Primarily, these symptoms are systemic and consist of fever sensation, true chills, headache, severe myalgia, malaise, and anorexia.

Mostly headache, myalgia, and fever determine the severity of the disease insofar as they are more prominent. These symptoms are mostly accompanied by the manifestations of respiratory tract illnesses such as dry cough, nasal discharge, and sore throat. Often, so abrupt is the onset that the patient can remember the precise onset of the disease.

However, the manifestations of influenza infections can range from afebrile respiratory illnesses similar to the common cold, to diseases in which systemic signs and symptoms predominate with relatively little respiratory tract infection symptoms. It may, nonetheless, last for 4 to 8 days. A convalescent period of some weeks may ensue, during which dry cough and malaise are the most salient complaints of the patient. The most important and common complication of influenza is pneumonia, not least in high-risk individuals.

Pneumonia may happen as a continuum of the acute influenza syndrome when caused by the influenza virus primary pneumonia or as a mixed viral and bacterial infection after a gap of a few days secondary pneumonia. The illness occurs after the typical course of flu with a rapid progression of fever, dyspnea, cough, cyanosis, and difficult breathing.

It happens predominantly among individuals with cardiovascular or underlying pulmonary diseases such as asthma. Physical examination is in favor of bilateral lung involvement, and imaging findings in the lungs constitute reticular or reticulonodular opacities with or without superimposed consolidation. Sometimes the radiological appearance of primary influenza pneumonia can be difficult to distinguish from pulmonary edema because of the presence of perihilar congestion and hazy opacification, at least in the lower lobes.

Less frequently, radiographs show focal areas of infiltration. Commonly used pneumonia severity assessment tools such as the CURB65 or the Pneumonia Severity Index are not useful in determining which patients to hospitalize due to primary influenza pneumonia since these tools have not been developed and validated during an influenza pandemic.

The typical radiographic findings of primary influenza pneumonia are bilateral reticular or reticulonodular opacities, sometimes accompanied by superimposed consolidation. Less frequently, radiographs show focal areas of consolidation without reticular opacities. High-resolution computed tomography often shows multifocal peribronchovascular or subpleural consolidation with or without ground-glass opacities.

These patients usually present with progressive dyspnea and severe hypoxemia 2 to 5 days after the onset of typical influenza symptoms. Hypoxemia increases rapidly and causes respiratory failure, requiring intubation and mechanical ventilation, maybe after only 1 day of hospitalization.

The patient has a classic influenza disease, followed by an improvement period lasting maximally 2 weeks. The recurrence of the symptoms such as fever, productive cough, and dyspnea and findings of new consolidations in chest imaging can be found in involved patients. Accordingly, a biphasic pattern of signs and symptoms in influenza-labeled patients should be considered as secondary superimposed bacterial pneumonia. In addition to its respiratory effects, the virus can exert effects on other body systems such as the musculoskeletal, cardiac, and neurologic systems.

Myocarditis and pericarditis constitute unusual but significant complications of seasonal or pandemic flu. In a prospective study, half of adult flu patients without cardiac complaints had abnormal ECG findings at presentation. Significant myositis and rhabdomyolysis have rarely been reported with seasonal influenza, 25 but different amounts of creatine phosphokinase elevation have been reported in many studies after seasonal or pandemic flues. The majority of influenza cases are diagnosed by their clinical manifestations and there is no need for laboratory tests.

Be that as it may, in special circumstances, the diagnosis of flu necessitates laboratory confirmation using available tests such as nucleic acid tests e. Rapid influenza diagnostic tests detect influenza viral antigens and screen patients with suspected influenza in a timely manner in comparison to other diagnostic modalities.

The most widely used technique is based on the detection of viral antigens in the respiratory secretions of patients by immunologic methods. All rapid tests are performed with ease and can provide results within 30 minutes. Each test varies with regard to whether it can distinguish between influenza A and B. Nevertheless, these tests have thus far been unable to specify types of influenza A such as H1N1 and H3N2.

The overall specificities achieved by these tests are high and comparable between the manufacturers. However, their sensitivities have shown great heterogeneity across studies depending on the nature of the samples tested and the patients, ranging from 4.

Also, the sensitivity may be higher at the onset of the disease, when a higher load of the virus exists. Economic studies comparing rapid testing to the clinical diagnosis of influenza remain inconclusive.

Due to the limitation in other diagnostic modalities in influenza detection, molecular assays have increasingly been considered the gold standard diagnostic method for the detection of the influenza virus in hospital-based diagnostic laboratories. Although several amplification methods have been developed, the majority of the current assays—particularly those used in clinical laboratories—are based on the PCR amplification method.

These tests have the ability to check several targets concurrently and thereby provide type and subtype information for each virus. Additionally, they have the ability to be adapted rapidly for the detection of novel targets; these features 41 played a critical role during the influenza pandemic of PCR is potentially more sensitive than cell culture, and it can detect the nonviable virus in samples.

The sensitivity of these tests is dependent on the sample site of the patient and is similar to that of the rapid tests. Higher sensitivity can be obtained by swab samples of a nasopharyngeal origin. PCR-based molecular assays have yielded excellent clinical utility for the detection and identification of influenza viruses at bedside as POC, and numerous Food and Drug Administration FDA -cleared commercial devices are now available. Given the self-limiting nature of the disease in otherwise healthy individuals, there is no need for diagnostic tests in all presenting cases.

Diagnostic tests should be conducted if the results of the test are thought to be able to influence subsequent clinical management and if the results of the test are deemed influential in decisions on the initiation of specific antiviral treatment, impact on other diagnostic tests, antibiotic treatment decision-making, and infection control practices. Currently, at least 4 antiviral drugs are available for the treatment and prevention of influenza.

It is deserving of note that in healthy immunocompetent individuals with intact immunity, there is a rapid limitation in the ability of the influenza virus; therefore, the anti-replication power of antiviral drugs is limited and has no theoretical effect. Also, no study to date has demonstrated a beneficial effect for antiviral agents starting beyond 48 hours of symptom onset. The greatest effect is classically seen when therapy is started in the first 24 hours.

Treatment is recommended for both adults and children with the influenza virus infection with the following criteria: Persons with laboratory-confirmed or highly suspected influenza virus infection in high-risk groups table 1 , within 48 hours after symptom onset. Patients requiring hospitalization for laboratory-confirmed or highly suspected influenza disease, regardless of underlying illnesses, if treatment can be initiated within 48 hours after symptom onset.

During the last pandemic wave, neuraminidase inhibitors NAIs —primarily oseltamivir and zanamivir—were widely prescribed for patients with confirmed or suspected A H1N1pdm09 infection.

Clinicians should be aware of the local patterns of influenza circulations and susceptibilities. For instance, a meta-analysis showed that NAIs were able to lessen mortality in patients admitted to the hospital with A H1N1pdm09 infection. However, most influenza A and B virus strains are still susceptible to neuraminidases such as oseltamivir and zanamivir, with these drugs being selected for treatment in indicated persons table 2. Recommended dosages and durations of influenza antiviral medications for treatment or chemoprophylaxis.

Due to the limitations in the current therapeutic options for the treatment of influenza virus infections, additional treatment options with a different mechanism of action have been investigated as treatment for individuals with severe influenza virus disease.

For example, a handful of mAbs against influenza virus proteins are currently in the early phases of evaluation for human infection control. The M2e is an attractive target for influenza vaccines and therapeutic antibodies because of the extremely conserved nature of the amino acid sequences of its domains among isolates from different subtypes of influenza A viruses.

The mechanisms of anti-M2e Ab—mediated protection are not completely determined. Anti-M2 Abs do not have hemagglutination inhibition ability or in vitro virus neutralization properties. Most studies have reported that corticosteroid therapy adversely influences influenza-related outcomes.

The most important strategy for the prevention of influenza and its severe outcomes is annual vaccination against seasonal influenza. Recently, the World Health Organization WHO recommended that trivalent influenza vaccines for use in the southern hemisphere influenza season contain the following virus antigens: The WHO stresses that vaccination is especially important for individuals at higher risk of serious influenza complications, with the highest priority afforded to pregnant ladies—followed by children aged between 6 and 59 months, elderly and individuals with specific chronic medical conditions e.

The outbreaks of influenza generally occur during the last autumn and whole winter months. A single dose 0. Children aged between 6 months and 8 years require 2 doses of influenza vaccine with at least 4 weeks apart during their 1st season of vaccination foroptimal response.

The vaccine effectiveness of influenza vaccines is a determinant of how much the seasonal influenza vaccine can prevent influenza virus infections in the given population during an influenza season. It is also a fact that influenza vaccines are safe and are especially important for reducing severe disease in some high-risk populations.

Accordingly, the WHO recommends seasonal influenza vaccines even if they are not closely related to the predominant circulating influenza viruses each year for the above-mentioned groups.

Available antiviral drugs play an important role for patients who have not been immunized or who are nonresponsive to vaccines. Oseltamivir and zanamivir are the recommended drugs for the prevention of influenza based on their established efficacy and low rates of resistance in comparison to adamantanes.

The efficacy of oseltamivir and zanamivir has yet to be compared with each other. There are, therefore, some indications for this approach, as follows: Influenza prophylaxis during influenza outbreaks in long-term care centers in the elderly regardless of prior influenza vaccinations.

In unvaccinated individuals at high risk of influenza complications who have been exposed to an individual with influenza infections within the previous 48 hours. Antiviral prophylaxis for vaccinated persons at high risk of influenza complications who have had close contact with an individual with influenza within the previous 48 hours when there is a poor match between the vaccine and circulating viruses in a given year.

Zanamivir may be the drug of choice for prophylaxis due to its limited systemic absorption. Influenza epidemics and pandemics impose a heavy socioeconomic burden on all societies. Hospital admission and treatment and ICU care are more often necessary in high-risk individuals such as the elderly and pregnant ladies.

However, the impact of influenza cannot be neglected even in young adults, mainly because of the loss of productivity. Given the nature of the virus and the increasing patterns of the available antiviral drugs against the influenza virus, the best strategy is the vaccination of high-risk groups table 1 at appropriate times. Inactivated influenza vaccines are always well-tolerated, with the most common side effect being burning pain at the injection site.

Consequently, the vaccination policy in high-risk groups should be the priority in the battle against flu. With concerns over increasing resistance against both adamantanes and NAIs, the risk of the development of antiviral drug resistance should be considered if we opt to treat all patients who are labeled as suffering from flu. Individuals with suspected flue with severe disease such as those with signs and symptoms of lower respiratory tract infections e.

In addition, a new look at antiviral chemoprophylaxis and its appropriate use may effect a reduction in morbidity and mortality allied to flu in high-risk groups. National Center for Biotechnology Information , U. Iran J Med Sci. Mohsen Moghadami , MD. Author information Article notes Copyright and License information Disclaimer.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3. Studies have found that inactivated influenza vaccines cannot cause influenza disease and are safe in pregnancy. Common side effects of vaccination include local injection site reactions and cold-like symptoms. Fever, malaise, and myalgia are less common. Influenza may be prevented or rendered less severe by post-exposure prophylaxis PEP with antivirals oseltamivir and zanamivir.

Who have had close contact with people with confirmed or suspected influenza that is, living in the same household or residential setting and. Able to start prophylaxis within 48 hours oseltamivir or 36 hours zanamivir of contact and. During an outbreak, consider isolation of residents of closed settings for the duration of the infectious period five days after symptom onset to limit spread to others. Cohorting of patients that is, in separate hospital bays or on separate floors of a residential home may be necessary.

Residential homes may need to be closed to new admissions until the outbreak is controlled. Care must be taken when discharging a patient from a ward with a known influenza outbreak to a care home, or vice versa. Vaccine candidates have recently been developed that can elicit antibodies against multiple influenza strains, and thus could overcome the need for annual influenza vaccines. What steps have you taken to improve the uptake of influenza vaccination among staff and eligible patients under your care?

Have you reviewed antivirals prescribed treatment or prophylaxis for eligible patients with influenza and their close contacts? Public Health England. Chapter Influenza. In: Immunisation Against Infectious Disease. National Institute for Health and Care Excellence. Clinical Knowledge Summaries: Influenza-seasonal. Use of neuraminidase inhibitors in influenza. Contributors: SG and PM conceived of the review. SG is the guarantor of the manuscript. PM designed and wrote code for the interactive application.

All authors have seen and approved the final manuscript version. Competing interests: We have read and understood BMJ policy on declaration of interests and declare that we have no competing interests.

Provenance and peer review: Not commissioned; externally peer reviewed. National Center for Biotechnology Information , U. Journal List BMJ v. Published online Dec 7. Sam Ghebrehewet , consultant in communicable disease control and head of health protection , 1 Peter MacPherson , academic clinical lecturer , 1 , 2 , 3 and Antonia Ho , specialty registrar in infectious diseases 4 , 5. Author information Copyright and License information Disclaimer.

Corresponding author: S Ghebrehewet ku. This article has been cited by other articles in PMC. What you need to know Influenza is an acute viral infection of the respiratory tract that spreads easily from person to person Influenza is usually self limiting in healthy individuals, with recovery in days Elderly people, children under 6 months old, pregnant women, and people with chronic conditions or immunosuppression are at increased risk of complications Offer influenza vaccination to people at risk of complications and increased influenza exposure, as well as to young children, who are efficient infection spreaders People in high risk groups may benefit from antiviral therapy, hospitalisation, or intensive care.

What is influenza virus? Open in a separate window. What are the symptoms of influenza? Box 1: Who should be prescribed antiviral treatment for influenza?

Individuals admitted to hospital with suspected or confirmed influenza. How do influenza epidemics and pandemics occur? Table 2 Antigenic drift versus antigenic shift: implications for epidemics and pandemics.

Antigenic drift Antigenic shift Accumulation of mutations in genes that code for antibody binding sites on viruses leading to emergence of new strains A sudden major change in the virus antigenicity Only one virus strain accumulation of point mutations From one or more virus strains from genome reassortment Occurs frequently Occurs occasionally Usually responsible for seasonal influenza epidemics and affects effectiveness of influenza vaccine Gives rise to pandemics, which occur irregularly and unpredictably due to a lack of immunity to the new strain in the human population Occurs in influenza virus A, B, and C Only occurs in influenza virus A.

How is influenza diagnosed? What treatments are available for influenza? How can influenza be prevented? Vaccination Vaccination is the most effective means of preventing influenza and its complications.

People at risk of influenza exposure or transmitting influenza to vulnerable groups Health and social care workers Individuals who live with or care for vulnerable people. People living in settings where rapid spread is likely after introduction of infection, potentially resulting in high morbidity and mortality Individuals living in long-stay care facilities. Antiviral chemoprophylaxis Influenza may be prevented or rendered less severe by post-exposure prophylaxis PEP with antivirals oseltamivir and zanamivir.

Table 3 Responding to influenza cases and clusters or outbreaks by setting. New developments in prevention and treatment of influenza Vaccine candidates have recently been developed that can elicit antibodies against multiple influenza strains, and thus could overcome the need for annual influenza vaccines. Education into practice What steps have you taken to improve the uptake of influenza vaccination among staff and eligible patients under your care?

Further educational resources Public Health England. How patients were involved in the production of this article No patients were involved in the production of this article. References 1. World Health Organization.

Influenza seasonal —Fact sheet No The burden of influenza in England by age and clinical risk group: a statistical analysis to inform vaccine policy. J Infect ; 68 Influenza vaccine viruses and reagents. Influenza D virus infection in Mississippi beef cattle.

Virology ; Characterization of a novel influenza virus in cattle and Swine: proposal for a new genus in the Orthomyxoviridae family.

MBio ; 5 :e A revision of the system of nomenclature for influenza viruses: a WHO memorandum. Bull World Health Organ ; 58 Evolution and ecology of influenza A viruses.

Microbiol Rev ; 56 Monitoring the impact of influenza by age: emergency department fever and respiratory complaint surveillance in New York City. PLoS Med ; 4 :e Influenza vaccination of schoolchildren and influenza outbreaks in a school. Clin Infect Dis ; 53