Antigenic and genetic analysis of the hemagglutinin of ~13,000 human influenza A (H3N2) viruses from six continents during 2002-2007 revealed that there was continuous circulation in east and ...Southeast Asia (E-SE Asia) via a region-wide network of temporally overlapping epidemics and that epidemics in the temperate regions were seeded from this network each year. Seed strains generally first reached Oceania, North America, and Europe, and later South America. This evidence suggests that once A (H3N2) viruses leave E-SE Asia, they are unlikely to contribute to long-term viral evolution. If the trends observed during this period are an accurate representation of overall patterns of spread, then the antigenic characteristics of A (H3N2) viruses outside E-SE Asia may be forecast each year based on surveillance within E-SE Asia, with consequent improvements to vaccine strain selection.
Abstract Annual influenza epidemics in humans affect 5–15% of the population, causing an estimated half million deaths worldwide per year Stohr K. Influenza—WHO cares. Lancet Infectious Diseases ...2002;2(9):517. The virus can infect this proportion of people year after year because the virus has an extensive capacity to evolve and thus evade the immune response. For example, since the influenza A(H3N2) subtype entered the human population in 1968 the A(H3N2) component of the influenza vaccine has had to be updated almost 30 times to track the evolution of the viruses and remain effective. The World Health Organization Global Influenza Surveillance Network (WHO GISN) tracks and analyzes the evolution and epidemiology of influenza viruses for the primary purpose of vaccine strain selection and to improve the strain selection process through studies aimed at better understanding virus evolution and epidemiology. Here we give an overview of the strain selection process and outline recent investigations into the global migration of seasonal influenza viruses.
Many countries consistently fail to achieve the target influenza vaccine coverage rate (VCR) of 75% for populations at risk of complications, recommended by the World Health Organization and European ...Council. We aimed to identify factors for achieving a high VCR in the scope of four benchmark countries with high influenza VCRs: Australia, Canada, UK and USA.
Publicly available evidence was first reviewed at a global level and then for each of the four countries. Semi-structured interviews were then conducted with stakeholders meeting predefined criteria. Descriptive cluster analyses were performed to identify key factors and pillars for establishing and maintaining high VCRs.
No single factor led to a high VCR, and each benchmark country used a different combination of tailored approaches to achieve a high vaccine coverage. In each country, specific triggers were important to stimulate changes that led to improved vaccine coverage. A total of 42 key factors for a successful influenza vaccination programme were identified and clustered into five pillars: (1) Health Authority accountability and strengths of the influenza programme, (2) facilitated access to vaccination, (3) healthcare professional accountability and engagement, (4) awareness of the burden and severity of disease and (5) belief in influenza vaccination benefit. Each benchmark country has implemented multiple factors from each pillar.
A wide range of factors were identified from an evaluation of four high-performing benchmark countries, classified into five pillars, thus providing a basis for countries with lower VCRs to tailor their own particular solutions to improve their influenza VCR.
The influenza viruses Hampson, Alan W; Mackenzie, John S
Medical journal of Australia,
11/2006, Letnik:
185, Številka:
S10
Journal Article
Recenzirano
Human epidemic influenza is caused by influenza type A and B viruses, which continually undergo antigenic change in their surface antigens, haemagglutinin (H) and neuraminidase (N).
Influenza ...epidemics are the consequence of small, ongoing antigenic changes known as “antigenic drift”, which occurs in both influenza types.
Pandemic influenza occurs at irregular and unpredictable intervals, and is the result of a major antigenic change known as “antigenic shift”, which occurs only in influenza A.
Aquatic birds are the evolutionary hosts of influenza viruses; they harbour many distinct forms or subtypes of influenza A, which are usually present as harmless gut infections.
Antigenic shift involves the evolution of a new human influenza A virus through the acquisition of a new haemagglutinin gene encoding a different subtype from an avian influenza, or by the adaptation of an avian virus, causing it to become transmissible between humans.
Two subtypes of avian influenza, H5 and H7, can cause severe infections when introduced into domestic poultry. Recently, influenza A/H5N1 viruses have caused widespread outbreaks, starting in Asia and spreading widely to other regions.
Avian influenza viruses do not readily infect humans. However, during the past 3 years, more than 250 cases of H5N1 infection of humans have occurred, with associated mortality approaching 60%. It is feared that a new pandemic of human influenza may emerge from this.
In many countries there is no clear recommendation regarding the preferred route of administration of inactivated influenza vaccines. In a randomised, observer blind study of 720 elderly subjects, a ...split, trivalent influenza vaccine was significantly more immunogenic for both A strains (H3N2 and H1N1,
p
=
0.0016 and 0.003, respectively) when given intramuscularly compared to subcutaneously. This difference was due entirely to a gender effect, with females in the intramuscular (IM) group having a significantly greater serological response than females in the subcutaneous (SC) group for both of these strains. Similar results were seen with local adverse effects. These data suggest that vaccination practices that ensure intramuscular injection are required for optimal administration of influenza vaccines in the elderly.
Fears of a potential pandemic due to A(H5N1) viruses have focussed new attention on our current vaccines, their shortcomings, and concerns regarding global vaccine supply in a pandemic. The bulk of ...current vaccines are inactivated split virus vaccines produced from egg-grown virus and have only modest improvements compared with those first introduced over 60 years ago. Splitting, which was introduced some years ago to reduce reactogenicity, also reduces the immunogenicity of vaccines in immunologically naïve recipients. The A(H5N1) viruses have been found poorly immunogenic and present other challenges for vaccine producers which further exacerbate an already limited global production capacity. There have been some recent improvements in vaccine production methods and improvements to immunogenicity by the development of new adjuvants, however, these still fall short of providing timely supplies of vaccine for all in the face of a pandemic. New approaches to influenza vaccines which might fulfil the demands of a pandemic situation are under evaluation, however, these remain some distance from clinical reality and face significant regulatory hurdles.
Human influenza viruses isolated from Australasia (Australia and New Zealand) and South East Asia were analysed to determine their sensitivity to the NA inhibitor drugs, zanamivir and oseltamivir. A ...total of 532 strains isolated between 1998 and 2002 were tested using a fluorescence-based assay to measure the relative inhibition of NA activity over a range of drug concentrations. Based on median IC
50 values, influenza A viruses (with neuraminidase subtypes N1 and N2) were more sensitive to both the NA inhibitors than were influenza B strains. Influenza A viruses with a N1 subtype and influenza B strains both demonstrated a greater sensitivity to zanamivir than to oseltamivir carboxylate, whereas influenza A strains with a N2 subtype were more susceptible to oseltamivir carboxylate. For each of the neuraminidase types, IC
50 values for viruses from Australasia and South East Asia were found to be comparable. Based on the data prior to and following the licensing of the drugs into the respective regions, the use of the NA inhibitors did not appear to have a significant impact on the susceptibility of the viruses tested to zanamivir or oseltamivir carboxylate.
It is impossible to predict when the next pandemic of influenza will occur; however, it is almost 35 years since the last pandemic, and the longest inter-pandemic interval recorded with certainty is ...39 years. The next pandemic virus is likely to emerge in southeast Asia, as have two of the last three pandemic viruses. Complete global spread is likely to occur in 6 months or less, due to increased travel and urbanisation. It is likely that the usual inter-pandemic pattern of age-specific mortality will deviate temporarily towards higher mortality in younger adults. The extent to which this will happen is unclear, as the shift was extreme in 1918–1919 but less so in subsequent pandemics. Nevertheless, this may have important implications for the protection of essential workers such as health care, emergency service and military personnel. The extent to which elderly persons will be affected will depend upon previous exposure to similar influenza viruses. It is impossible to predict the likely increase in excess mortality that will occur when a new pandemic virus emerges. However, whilst mortality on the scale experienced in 1918–1919 is probably unlikely, there was a high level of mortality among those infected with the A/H5N1 virus in 1997, so it cannot be assumed that a future pandemic will be as mild as those in 1957–1958 or 1968–1969. There is likely to be more than one wave of infection and health services in most countries will be hard pressed to provide vaccines or to manage populations with clinical attack rates of ≈25–30% and concomitant increases in demand for both primary and secondary health care services.
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