From the Guidelines
Influenza A is a type of influenza virus that causes epidemic human disease in a seasonal pattern, further classified into subtypes based on surface antigens hemagglutinin and neuraminidase.
Key Characteristics of Influenza A
- Influenza A viruses are responsible for seasonal flu outbreaks and can be further separated into groups based on other antigenic characteristics 1.
- Immunity to surface antigens protects individuals against infection and severe disease, but antibodies against one influenza virus type or subtype confer little or no immunity against other types and subtypes 1.
- Frequent antigenic changes, known as antigenic drift, generate new influenza virus variants that cause seasonal epidemics, and pandemic influenza may occur when a new influenza A virus emerges in humans through antigenic shift 1.
Clinical Implications
- Influenza A can exacerbate underlying medical conditions, including cardiovascular disease and diabetes, and can also lead to viral pneumonia, secondary bacterial pneumonia, or co-infection with other viruses or bacteria 1.
- Risks for complications, hospitalizations, and death from influenza are higher for individuals at the extremes of age and for persons with chronic medical conditions than for healthy older children and younger adults 1.
Prevention and Management
- Annual influenza vaccination is the primary mode of prophylaxis against influenza, with the US Advisory Committee on Immunization Practices recommending vaccination for all persons 50 years of age, children 6 months to 59 months of age, women who will be pregnant during influenza season, and adults and children with chronic conditions 1.
- Antiviral medications may be used for short-term prophylaxis of high-risk persons with known exposure to a case of influenza, as well as for treatment of influenza cases, but are not recommended as a general preventive strategy at the population level 1.
From the Research
Definition of Influenza A
Influenza A, also known as Influenza type A, is a type of influenza virus that can cause illness in humans.
Characteristics of Influenza A
- Influenza A is a potentially life-threatening illness that affects approximately 10% of the population annually, with resulting personal misery and societal disruption 2.
- It can cause significant morbidity and mortality in young children, the elderly, pregnant and post-partum women, patients with co-morbidities and the immunocompromised 3.
- Influenza A can be a self-limiting illness in healthy individuals but is associated with short-term morbidity and economic burden 3.
Treatment of Influenza A
- Neuraminidase inhibitors (NAIs) are the treatment of choice for influenza due to widespread resistance to the adamantanes 3.
- Oseltamivir is a novel influenza treatment that has been extensively investigated and is effective in treating influenza in adult populations, including the elderly and patients with chronic cardiac and/or respiratory disease 2.
- Early treatment with NAIs has been shown to reduce otitis media in children, and lower respiratory tract complications, resulting in antibiotic therapy, in adults 3.
- Peramivir is no less effective than oseltamivir in the treatment of severe influenza A with primary viral pneumonia, and patients treated with peramivir had significantly shorter remission times of fever symptoms than those treated with oseltamivir 4.
Efficacy of Oseltamivir
- Oseltamivir treatment resulted in a modest reduction in the duration of symptoms and virus shedding in people with uncomplicated influenza infections, even when treatment was started 48 h or longer after illness onset 5.
- The median duration of symptoms was reduced by 1 day in the group given oseltamivir who were enrolled less than 48 h since symptom onset compared with those given placebo 5.
- Oseltamivir significantly reduced virus isolation on days 2,4, and 7 in participants enrolled less than 48 h since illness onset 5.