What's New with Influenza?

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Pandemic Influenza

WHO comes out with report with cumulative number of confirmed human cases of Avian Influenza A (H5N1)

 

2007:                       Total cases=86       Total deaths=59

Cambodia:                                         1 case                                       1 death

China:                                                5 cases                                      3 deaths

Egypt:                                                25 cases                                    9 deaths

Indonesia:                                          42 cases                                    37 deaths

Lao People's Democratic Republic:       2 cases                                      2 deaths

Myanmar:                                           1 case

Nigeria:                                              1 case                                       1 death

Pakistan:                                            1 case                                       1 death

Viet Nam:                                           8 cases                                      5 deaths

2008 (as of March 11): Total Cases=23       Total Deaths=18

China:                                                 3 cases                                    3 deaths

Egypt:                                                 4 cases                                    1 death

Indonesia:                                           12 cases                                  10 deaths

Viet Nam:                                           4 cases                                     4 deaths

2003-2008:                Total Cases=372     Total Deaths=235

Azerbaijan:                                         8 cases                                    5 deaths

Cambodia:                                          7 cases                                     7 deaths

China:                                                 30 cases                                  20 deaths

Djibouti:                                              1 case

Egypt:                                                 47 cases                                  20 deaths

Indonesia:                                           129 cases                                105 deaths

Iraq:                                                   3 cases                                     2 deaths

Lao People's Democratic Republic:         2 cases                                    2 deaths

Myanmar:                                             1 case                                    0 deaths

Nigeria:                                               1 case                                     1 death

Pakistan:                                             1 case                                     1 death

Thailand:                                             25 cases                                 17 deaths

Turkey:                                               12 cases                                  4 deaths

Viet Nam:                                            105 cases                                51 deaths  

Image 6 and Reference 8

Seasonal Influenza

2007-2008 Influenza Season

Epidemiology

    The 2007-08 influenza season in the United States began with very low activity until December. Influenza cases increased from early December until February 16th, and have decreased since. Although Influenza A H1N1 and H3N2 were both causing illness at the same time, H1N1 was more frequent until mid-January. Since the week of January 20th, H3N2 cases have increased substantially, and now outnumber H1N1 cases, becoming the most common subtype for the season.

Circulating Influenza Strains

    Viruses are labeled with four characteristics: the influenza virus type, the place of origin, the year in which it occurred, and the surface glycoprotein types. In the United States, most of the viruses of the 2007-08 season have been A/Brisbane/10/2007 (H3N2). Clearly, the virus started in Brisbane, Australia in early 2007. It spread to Europe and much of the southern hemisphere during the flu season of 2006-07, and viruses like this strain have been detected throughout the United States during the 2007-08 season.

Vaccine-Virus Match

    The vaccine that was created for the 2007-08 flu season included an A/Wisconsin (H3N2)-like strain related to, but not matched with the A/Brisbane/10/2007 (H3N2). The circulating B virus strain was also not matched with the B strain included in the 2007-08 vaccine. Therefore, protection from the flu vaccine for A H3N2 and B viruses was not optimal. Despite this, some protection can still come from the vaccine, since antibodies created from the vaccine can cross-protect against the circulating influenza virus, as they are closely related. 80% of the tested H1N1 viruses have been matched to the H1N1 strain included in the vaccine.

Drug Resistance 

    The influenza viruses that circulated during the 2007-08 season showed some drug resistance. The most resistance was observed to adamantanes. As of February 23rd, 98.9% of Influenza A H3N2 and 4.7% of Influenza A H1N1 were resistant to adamantanes. For this reason, the CDC has recommended that adamantanes be excluded from influenza treatments this season. Low levels of resistance was observed to oseltamivir, with 9.6% of H1N1 viruses showing resistance. No resistance to oseltamivir was observed for Influenza B viruses or Influenza H3N2, so oseltamivir is still a recommended antiviral. 

Reference 9

New Developments with Influenza

CDC Advisory Committee changes recommendations for influenza vaccine age range

Young infants are of particular risk to seasonal influenza infection, as their immune systems are not as strong as those of adults. For this reason, the CDC has recommended that children ages 6 months to 59 months receive a seasonal influenza vaccine. Recently, the CDC advisory committee has recommended that all children ages 6 months to 18 years of age be vaccinated. This would increase the number of children recommended to receive a vaccine by 30 million. (Reference 10).

Scientists discover what changes need to be made for human-to-human transmission of H5N1. 

Recent technology has allowed researchers to see what kinds of mutations must occur in order for the H5N1 virus to transmit from human to human. They found that the H protein must mutate in such a way that it would recognize and bind to cellular receptors with an umbrella-like topology. Currently, the avian H5N1 anti-receptors recognize cone-like receptors. (Reference 11).

Mechanism for amantadine resistance discovered

In an article published in the January edition of Nature, Penn researchers describe their discovery of the structural basis by which influenza A viruses can become resistant to amantadine, and another opportunity for drug therapy. Amantadine normally works by blocking the M2 proton channel, thereby inhibiting the viral uncoating process, and preventing the virus from infecting the cell. Influenza viruses that have developed resistance to amantadine have a mutation in the M2 proton that changes its shape so that amantadine cannot fit in the channel and block its function. However, the research team also identified another pocket in a channel next to the M2 proton channel that is conserved in all influenza A viruses. This could be an opportunity for new antiviral drugs, which could offset the growing resistance to amantadine. (Reference 12).