How Safe Is H5N1?

Avian influenza is an infection caused by avian (bird) influenza (flu) viruses (CDC). It is widely presumed that these influenza viruses occur naturally among birds. Wild birds in particular are suspect for carrying the virus in their intestines, but sickness from the virus is often rare. However, avian influenza appears to be extremely contagious among some domesticated birds (e.g., chickens, ducks and turkeys), which is some cases, can be fatal.

It has widely believed that infected birds often have the opportunity to shed the influenza virus in their saliva and feces. The infection among domesticated bird happens, when [these] birds come in contact with contaminated secretions or excretions; or even contaminated surfaces from other infected birds. This often happens [with poultry] with the dirt or cages or even materials that may have been contaminted by infected birds (FDA; USDA).

According to the United State Department of Agriculture (USDA), domesticated poultry cases have presented this disease in two forms of pathogenicity.”Low” and “high”. The “low” pathogenic form may go undected and in some cases, has presented mild symptoms, which include: ruffled feathers and decreased egg production. “High” pathogenic forms has been the most significant area of concern in terms of global public health. This particular pathogenic form has been responsible for 95% of fatal cases of domesticated birds worldwide. The first case of low pathogenic H5N1 was presented in the US in 1975 in a wild duck and in 1986 the same form of virulence presented in a wild mallard (USDA).

“HPAI H5N1 has not been detected in the United States. However, other strains of HPAI have been detected and eradicated three times in the United States: in 1924, 1983 and 2004. No significant human illness resulted from these outbreaks (USDA).” This is why prevention efforts must materialize meaningful results.

There has been a great deal of discussion of the development of an appropriate vaccine to counter this “high” pathnogenic form H5N1. There are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. All known subtypes of influenza A viruses can be found in birds (CDC).

According to most avian flu experts, the risk from avian influenza is generally low to most people {with the exception of those with compromised immune systems) because the viruses do not usually infect humans. This scenario has changed. There are several confirmed cases of human infection fom several subtypes of avian influenza infecton with the first report in 1997.

“Human influenza virus” usually refers to those subtypes that spread widely among humans. There are only three known A subtypes of influenza viruses (H1N1, H1N2, and H3N2) currently circulating among humans. It is likely that some genetic parts of current human influenza A viruses came from birds originally. Influenza A viruses are constantly changing, and they might adapt over time to infect and spread among humans (CDC, FDA).

What is critical about an avian outbreak among poultry, is the possible risk to people who have contact with infected birds or [even] contaminated surfaces. Symptoms of avian influenza in humans have typically ranged from human influenza-like symptoms (coughing, fever, etc). With the possibility of developing to life-threatening complications (eye infections, acute respiratory distress, etc.).

A randomized study that comprised 300 healthy volunteers yielded a promising finding. Volunteers were from both genders and ranged from age 18-40, received a vaccine [3 doses in total] of hemagglutinin, with or without a fixed dose of aluminum hydroxide as an adjuvant. The French and British invesitgators investigated the the safety and immunogenicity of a monovalent, inactivated, split-virion vaccine, derived from a highly pathogenic strain of H5N1 influenza that was obtained from an infected patient. According to the study, each subject two doses of vaccine 21 days apart, and sera collected on days 0, 21, and 42 were analyzed for hemagglutination-inhibiting and neutralizing antibodies.

One of the highlights for the study presented on day 42, in which 67% (223) of the subjects who received the highetst dose of hemagglutinin with adjuvant exhibited detectable antibody titer. 61% of the subjects also had positive hemagglutination-inhibition responses. Which appears to suggest some safety protection for the participants.

A similar finding was yielded in a similar study in the New England Journal of Medicine (March, 2006). Study investigators provided 451 study participants a two-dose regimen of 90 µg of subvirion influenza A (H5N1). The vaccine did not cause severe side effects and, in the majority of recipients, generates neutralizing antibody responses typically associated with protection against influenza. A conventional subvirion H5 influenza vaccine may be effective in preventing influenza A (H5N1) disease in humans.

I am hopeful that future studies will continue to explore this area of research with larger sample sizes, that will particularly examine the clinical effectiveness of the H5N1 in humans, as we look to eradicate this virus.


US Department of Agriculture. [Online]. AVIAN INFLUENZA Low-Pathogenicity H5N1 vs. High-Pathogenicity H5N1. Retrieved July 31, 2006 from www. usda.gov.

Centers for Disease Control and Prevention. [Online].Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus. Retrieved July 31, 2006 from www.cdc.gov

Bresson JL et al. Safety and immunogenicity of an inactivated split-virion influenza A/Vietnam/1194/2004 (H5N1) vaccine: Phase I randomised trial. Lancet 2006 May 20; 367:1657-64.

Treanor, J., Campbell, J., Zangwill, K., Rowe, T. and Wolff, M. (2006). Safety and Immunogenicity of an Inactivated Subvirion Influenza A (H5N1) Vaccine. Volume 354:1343-1351 March 30, 2006 Number 13.

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