On June 11, 2009, the World Health Organization (WHO) reported a global pandemic of novel influenza A (H1N1). The pandemic alert was raised to Phase 6. Over 70 countries have reported cases of novel influenza A (H1N1). A pandemic simply describes person to person transmission of this virus on multiple continents. It does not describe the severity of the pandemic. The current H1N1 strain is not nearly as virulent as the strain that caused the 1918 pandemic. In fact, there are much fewer cases of Inflenza A H1N1 infections, hospitalizations and deaths compared to the current seasonal influenza A strain.
Origin of Novel Influenza Virus A H1N1
Initially, influenza A H1N1 was felt to be of swine origin. Indeed, swine influenza viruses have been isolated in the United States since 1930. The current H1N1 Influenza A strain is a novel combination of swine, avian and human genetic components. Pigs can be infected with both human and bird (Avian) forms of influenza viruses.
Humans are typically (with the exception of certain avian origin strains in 2003 and 2006) resistant to the direct transfer of avian influenza virus strains. However, avian forms can infect pigs. Typically the spread is from wild waterfowl such as ducks. If pigs are infected with more than one strain of bird and human influenza virus, re-assortment of the genes can occur, and a novel virus subtype forms.
Importance of the Hemagglutanin (H) Protein of Influenza A Viruses
Molecules on the surface of influenza strains define the specific strain of the virus. The H stands for the particular hemagglutanin molecule on a influenza strain and the N stands for the type of neuraminidase molecule on the surface of virus. When a new strain of influenza virus develops (antigenic shift) , such as novel influenza A virus H1N1, humans do not have significant immunity to the strain and a pandemic can occur. Note that there can be different H1N1 viruses, with novel combination of human, swine and avian origin.
When a pig or human develops immunity to an influenza virus, it is because antibodies are formed to the specific hemagglutinin protein of a particular viral strain. So any vaccine developed to a specific influenza A strain must contain antigens of the H protein of the strain of interest. There is an influenza A vaccine for pigs, but it will not confer immunity to humans. Similarly, antibodies which develop by exposure to a seasonal influenza A viral strain (Say H3N2) will NOT provide immunity to the current novel influenza A virus H1N1.
Social distancing measures, public awareness of methods to prevent spread of the virus, including hand washing and using and then discarding tissues infected with any upper respiratory viral infection have all been successful in limiting the spread of disease.
Vaccine Development is Underway
The US Centers for Disease Control has isolated the new H1N1 strain, and based on this information, developed a strain that can be used to make an H1N1 vaccine. Large amounts of the antigen, or viral parts, are required to generate immunity in humans. An adjuvent molecule or additional component added to the vaccine can boost the immune response to a given antigen. Contracts with five vaccine manufacturers have been made by the United States Health and Human Services department. The National Institutes of Health will carry out clinical trials in humans to evaluate the immune response and safety profile of the influenza A H1N1 vaccine. The H1N1 strains isolated in patients all over the world share a remarkable similarity, increasing the chance that the vaccine developed against this worldwide strain will be highly effective against this particular strain.
Populations Targeted for Initial Vaccination
The CDC has outlined recommendations for target populations to receive vaccination when available. If supplies of H1N1 vaccine are limited, certain populations, who have been found to be disproportionately affected by this novel Influenza A strain, will receive priority vaccination. People of all ages who work in child care centers should receive vaccination. Children over age 6 months who are in child care centers should also be vaccinated.
Students and staff of all ages of schools Kindergarten through twelfth grade should also be high priority to receive vaccination. This is because novel influenza A virus H1N1 has affected mostly healthy younger people, including children and pregnant women. This is in contrast to seasonal influenza, which disproportionately affects elderly patients. Children over age 6 mos to 4 years of age should also receive the vaccine. Household contacts of children under age 6 months should be vaccinated to prevent babies under 6 months of age from contracting influenza A H1N1.
It is hoped that the H1N! virus does not mutate before an effective vaccine can be manufactured. Public Health officials in many states and countries are gearing up for the large scale vaccination of people at risk for influenza A novel virus H1N1.
This article is for informational purposes only and should not substitute for medical advice from your health care provider. The author is not providing personal medical opinion, diagnosis or course of treatment. Do not delay or substitute this information for medical treatment.
Vandana Bhide - Vee Bhide, M.D. is a board certified Internist and Pediatrician. She graduated from college and medical school at the University of ...
