Did the 2009 Influenza A (H1N1) Virus Caused more Severe Infection than Seasonal Influenza during 2009 to 2010 Season?

ABSTRACT Human influenza pandemics occur when influenza viruses to which the population has little or no immunity emerge and acquire the ability to achieve human-to-human transmission. In April 2009, cases of a novel H1N1 influenza virus in children in the southwestern United States were reported. It was retrospectively shown that these cases represented the spread of this virus from an ongoing outbreak in Mexico. The emergence of the pandemic led to a number of national vaccination programs. Surprisingly, early human clinical trial data have shown that a single dose of nonadjuvanted pandemic influenza A (H1N1) 2009 monovalent inactivated vaccine (pMIV) has led to a seroprotective response in a majority of individuals, despite earlier studies showing a lack of cross-reactivity between seasonal and pandemic H1N1 viruses. Here we show that previous exposure to a contemporary seasonal H1N1 influenza virus and to a lesser degree a seasonal influenza virus trivalent inactivated vaccine is able to prime for a higher antibody response after a subsequent dose of pMIV in ferrets. The more protective response was partially dependent on the presence of CD8+ cells. Two doses of pMIV were also able to induce a detectable antibody response that provided protection from subsequent challenge. These data show that previous infection with seasonal H1N1 influenza viruses likely explains the requirement for only a single dose of pMIV in adults and that vaccination campaigns with the current pandemic influenza vaccines should reduce viral burden and disease severity in humans.

Download Full-text

The Emergence of Oseltamivir-Resistant Seasonal Influenza A (H1N1) Virus in Korea During the 2008–2009 Season

Osong Public Health and Research Perspectives ◽

10.1016/j.phrp.2011.11.042 ◽

2011 ◽

Vol 2 (3) ◽

pp. 178-185 ◽

Cited By ~ 8

Author(s):

Woo-Young Choi ◽

Inseok Yang ◽

Sujin Kim ◽

Namjoo Lee ◽

Meehwa Kwon ◽

...

Keyword(s):

Influenza A ◽

Seasonal Influenza ◽

H1n1 Virus ◽

Influenza A H1n1

Download Full-text

Complications and Outcomes of Pandemic 2009 Influenza A (H1N1) Virus Infection in Hospitalized Adults: How Do They Differ From Those in Seasonal Influenza?

The Journal of Infectious Diseases ◽

10.1093/infdis/jir187 ◽

2011 ◽

Vol 203 (12) ◽

pp. 1739-1747 ◽

Cited By ~ 85

Author(s):

N. Lee ◽

P. K. S. Chan ◽

G. C. Y. Lui ◽

B. C. K. Wong ◽

W. W. Y. Sin ◽

...

Keyword(s):

Virus Infection ◽

Influenza A ◽

Seasonal Influenza ◽

H1n1 Virus ◽

Influenza A H1n1 ◽

H1n1 Virus Infection

Download Full-text

Residual immunity in older people against the influenza A(H1N1) – recent experience in northern Spain

Eurosurveillance ◽

10.2807/ese.14.39.19344-en ◽

2009 ◽

Vol 14 (39) ◽

Cited By ~ 16

Author(s):

E Pérez-Trallero ◽

L Piñeiro ◽

D Vicente ◽

M Montes ◽

G Cilla

Keyword(s):

Pandemic Influenza ◽

Influenza A ◽

Seasonal Influenza ◽

H1n1 Virus ◽

Influenza Pandemic ◽

Age Groups ◽

H3n2 Virus ◽

Recent Experience ◽

Northern Spain ◽

Influenza A H1n1

The 2009 pandemic influenza A(H1N1) virus has a higher incidence in children and young adults, a pattern that has also been reported in seasonal influenza caused by the influenza A(H1N1) virus. We analysed age at infection in symptomatic patients with influenza in the Basque Country (northern Spain), reported through the sentinel influenza surveillance system which monitors 2.2-2.5% of the population. Between September 1999 and August 2009, influenza A(H3N2) or seasonal influenza A(H1N1) was detected in 941 patients, and from April to August 2009, pandemic influenza A(H1N1) was detected in 112 patients. The H3/H1 seasonal influenza ratio was between 3.3 and 3.4 in the under 60 year-olds, but 9.8 in older individuals, suggesting that people born before 1950 have residual immunity against the influenza A H1N1 subtype (both seasonal and pandemic). Introduction In 1957, the Asian influenza pandemic was caused by influenza A(H2N2) virus, which circulated until 1968 when it was displaced by the influenza A(H3N2) virus which was responsible for the Hong Kong pandemic. Before 1957, direct descendants of the influenza A(H1N1) virus that had caused the 1918 pandemic (Spanish flu) had circulated. In 1977, an influenza A(H1N1) strain re-emerged, which, together with the dominant influenza A(H3N2) strain, has been the cause of seasonal human influenza for more than three decades [1]. Despite the prolonged co-circulation of both subtypes, few studies have analysed their ability to affect distinct age groups. The current pandemic influenza A(H1N1) virus, influenza A(H1N1)v, which emerged in the spring of 2009, has spread throughout the world. The aim of this study was to compare the distribution in distinct age groups of infections caused by the two subtypes of seasonal influenza in the past 10 seasons and refer therelate this to recent infections due to influenza A(H1N1)v.

Download Full-text

High frequency of cross-reacting antibodies against 2009 pandemic influenza A(H1N1) virus among the elderly in Finland

Eurosurveillance ◽

10.2807/ese.15.05.19478-en ◽

2010 ◽

Vol 15 (5) ◽

Author(s):

N Ikonen ◽

M Strengell ◽

L Kinnunen ◽

P Österlund ◽

J Pirhonen ◽

...

Keyword(s):

Influenza Virus ◽

Pandemic Influenza ◽

Influenza A ◽

Seasonal Influenza ◽

H1n1 Virus ◽

The Elderly ◽

Influenza Viruses ◽

Spanish Influenza ◽

Pandemic Virus ◽

Influenza A H1n1

Since May 2009, the pandemic influenza A(H1N1) virus has been spreading throughout the world. Epidemiological data indicate that the elderly are underrepresented among the ill individuals. Approximately 1,000 serum specimens collected in Finland in 2004 and 2005 from individuals born between 1909 and 2005, were analysed by haemagglutination-inhibition test for the presence of antibodies against the 2009 pandemic influenza A(H1N1) and recently circulating seasonal influenza A viruses. Ninety-six per cent of individuals born between 1909 and 1919 had antibodies against the 2009 pandemic influenza virus, while in age groups born between 1920 and 1944, the prevalence varied from 77% to 14%. Most individuals born after 1944 lacked antibodies to the pandemic virus. In sequence comparisons the haemagglutinin (HA) gene of the 2009 pandemic influenza A(H1N1) virus was closely related to that of the Spanish influenza and 1976 swine influenza viruses. Based on the three-dimensional structure of the HA molecule, the antigenic epitopes of the pandemic virus HA are more closely related to those of the Spanish influenza HA than to those of recent seasonal influenza A(H1N1) viruses. Among the elderly, cross-reactive antibodies against the 2009 pandemic influenza virus, which likely originate from infections caused by the Spanish influenza virus and its immediate descendants, may provide protective immunity against the present pandemic virus.

Download Full-text

Risk groups and other target groups – preliminary ECDC guidance for developing influenza vaccination recommendations for the season 2010-11

Eurosurveillance ◽

10.2807/ese.15.12.19525-en ◽

2010 ◽

Vol 15 (12) ◽

Cited By ~ 1

Author(s):

H Nokleby ◽

A Nicoll

Keyword(s):

Influenza Vaccination ◽

Influenza A ◽

Seasonal Influenza ◽

H1n1 Virus ◽

Risk Groups ◽

Evidence Based ◽

Target Groups ◽

Rigorous Approach ◽

Vaccination Recommendations ◽

Influenza A H1n1

Providing guidance on risk and target groups for seasonal influenza immunisation is difficult for the 2010-11 season since there is no experience with the new influenza A(H1N1) virus in its seasonal form. Arguments exist for offering immunisation to people with chronic illness and older people, and also for other risk and target groups including pregnant women. A more rigorous approach is being developed to produce annual evidence-based guidance on risk and target groups for influenza vaccination.

Download Full-text

Cross-protective immunity against influenza pH1N1 2009 viruses induced by seasonal influenza A (H3N2) virus is mediated by virus-specific T-cells

Journal of General Virology ◽

10.1099/vir.0.033076-0 ◽

2011 ◽

Vol 92 (10) ◽

pp. 2339-2349 ◽

Cited By ~ 91

Author(s):

Marine L. B. Hillaire ◽

Stella E. van Trierum ◽

Joost H. C. M. Kreijtz ◽

Rogier Bodewes ◽

Martina M. Geelhoed-Mieras ◽

...

Keyword(s):

T Cells ◽

Influenza Virus ◽

Virus Infection ◽

Protective Immunity ◽

Influenza A ◽

Seasonal Influenza ◽

H1n1 Virus ◽

H3n2 Virus ◽

Influenza A H1n1 ◽

H1n1 Virus Infection

Influenza A (H1N1) viruses of swine origin were introduced into the human population in 2009 and caused a pandemic. The disease burden in the elderly was relatively low, which was attributed to the presence of cross-reacting serum antibodies in this age group, which were raised against seasonal influenza A (H1N1) viruses that circulated before 1957. It has also been described how infection with heterosubtypic influenza viruses can induce some degree of protection against infection by a novel strain of influenza virus. Here, we assess the extent of protective immunity against infection with the 2009 influenza A (H1N1) pandemic influenza virus that is afforded by infection with a seasonal influenza A (H3N2) virus in mice. Mice that experienced a primary A (H3N2) influenza virus infection displayed reduced weight loss after challenge infection and cleared the 2009 influenza A (H1N1) virus infection more rapidly. To elucidate the correlates of protection of this heterosubtypic immunity to pandemic H1N1 virus infection, adoptive transfer experiments were carried out by using selected post-infection lymphocyte populations. Virus-specific CD8+ T-cells in concert with CD4+ T-cells were responsible for the observed protection. These findings may not only provide an explanation for epidemiological differences in the incidence of severe pandemic H1N1 infections, they also indicate that the induction of cross-reactive virus-specific CD8+ and CD4+ T-cell responses may be a suitable approach for the development of universal influenza vaccines.

Download Full-text