Subcutaneous immunization with baculovirus surface-displayed hemagglutinin of pandemic H1N1 Influenza A virus induces protective immunity in mice

The protective immunity of baculovirus displaying influenza virus hemagglutinin (BacHA) against influenza 2009 H1N1 virus infection in a murine model was investigated. The results showed that mice vaccinated with live BacHA or an inactive form of adjuvanted BacHA had enhanced specific antibody responses and induced protective immunity against 2009 H1N1 virus infection, suggesting the potential of baculovirus as a live or inactivated vaccine.     

Sero‐immunity and serologic response to pandemic influenza A (H1N1) 2009 virus in Hong Kong

To study the serologic response to the new pandemic influenza A (H1N1) 2009 virus in Hong Kong, the level of immunity was measured before and after the occurrence of the outbreak, and the titer of antibody to the pandemic influenza A (H1N1) 2009 virus in serum samples of laboratory confirmed cases. The presence of pre‐outbreak pandemic influenza A (H1N1) 2009 virus antibodies in 37% of individuals older than >65 years suggested previous exposures to heterologous virus strains may have elicited cross‐reacting antibody. Following large outbreaks of pandemic influenza A 2009 virus that peaked in September 2009, there is a change in immunity level in various age groups consistent with the attack rates among population in Hong Kong. Among individuals with mild clinical presentation, the antibody response to pandemic influenza A (H1N1) 2009 virus was stronger in those individuals aged ≤24 years but took more time to reach a titer of 40 when compared with those aged >24 years; however, the antibody level declined slower among individuals aged ≤24 years. Regardless of age, the antibody response rose rapidly and reached much higher titer among individuals with severe clinical presentation. Further study is required to collect additional data on antibody persistence and determine how much protection is conferred by previous exposure to seasonal influenza A (H1N1) viruses. J. Med. Virol. 82:1809–1815, 2010. © 2010 Wiley‐Liss, Inc.     

Reduced antibody responses to the pandemic (H1N1) 2009 vaccine after recent seasonal influenza vaccination

The vaccination program against the 2009 pandemic H1N1 influenza virus (2009 H1N1) provided a unique opportunity to determine if immune responses to the 2009 H1N1 vaccine were affected by a recent, prior vaccination against seasonal influenza virus. In the present study, we studied the immune responses to the 2009 H1N1 vaccine in subjects who either received the seasonal influenza virus vaccination within the prior 3 months or did not. Following 2009 H1N1 vaccination, subjects previously given a seasonal influenza virus vaccination exhibited significantly lower antibody responses, as determined by hemagglutination inhibition assay, than subjects who had not received the seasonal influenza virus vaccination. This result is compatible with the phenomenon of "original antigenic sin," by which previous influenza virus vaccination hampers induction of immunity against a new variant. Our finding should be taken into account for future vaccination programs against pandemic influenza virus outbreaks.     

Immunization with a low dose of hemagglutinin-encoding plasmid protects against 2009 H1N1 pandemic influenza virus in mice

A vaccine against the novel pandemic influenza virus (2009 H1N1) is available, but several problems in preparation of vaccines against the new emerging influenza viruses need to be overcome. DNA vaccines represent a novel and powerful alternative to conventional vaccine approaches. To evaluate the ability of a DNA vaccine encoding the hemagglutinin (HA) of 2009 H1N1 to generate humoral responses and protective immunity, BALB/c mice were immunized with various doses of 2009 H1N1 HA-encoding plasmid and anti-HA total IgG, hemagglutination inhibition antibodies and neutralizing antibodies were assayed. The total IgG titers against HA correlated positively with the doses of DNA vaccine, but immunization with either a low dose (10 μg) or a higher dose (25-200 μg) of HA plasmid resulted in similar titers of hemagglutination inhibition and neutralizing antibodies, following a single booster. Further, 10 μg plasmid conferred effective protection against lethal virus challenge. These results suggested that the DNA vaccine encoding the HA of 2009 H1N1 virus is highly effective for inducing neutralizing antibodies and protective immunity. DNA vaccines are a promising new strategy for the rapid development of efficient vaccines to control new emerging pandemic influenza viruses.     

Antibody prevalence to the 2009 pandemic influenza A (H1N1) virus in Germany: geographically variable immunity in winter 2010/2011

Location- and age-specific prevalence of antibodies against 2009 pandemic influenza A (H1N1) virus were determined in sera of blood donors collected during winter 2010/2011 in Germany. Prevalence of antibodies at protective titres (HI ≥1:40) varied significantly between cities (24.13–83.67 %) throughout all age groups. However, high level antibodies (HI >1:80) were most prevalent among young individuals (18–29 and 30–39 years). Overall, this study demonstrates that older people (50–59 and 60–70 years) are no longer more likely to present protective antibody titres against 2009 pandemic influenza A (H1N1) virus than younger individuals. Furthermore, our data show a highly variable immunity among the German population in different major cities almost 2 years after the detection of first cases in Germany.     

Relationship of Th1/Th2 cell balance with the immune response to influenza vaccine during pregnancy

To determine the optimal timing for influenza vaccination in pregnant women, we measured alterations in the types 1 and 2 T helper cell (Th1/Th2) balance during pregnancy, monitored specific immunity to inoculated antigens after vaccination with inactivated influenza vaccine, evaluated the relevance of the Th1/Th2 ratio and immune responses to the vaccination, monitored the maintenance of high antibody titers until delivery and measured the transplacental antibody transfer rate. No significant alterations of the Th1/Th2 balance were noted in the 65% of pregnant women among whom the Th1/Th2 ratio was lower than 9.9% in the first trimester. In those groups with a ratio higher than 10% in the first trimester, there was a tendency for the ratio to decrease as gestation advanced. The efficiency of immunization was not influenced by the Th1/Th2 status or by the stage of gestation. The antibody titer decreased steadily with time from 1 month after vaccination to the time of delivery. Conversely, the transfer rate of antibodies from maternal to fetal blood at the time of delivery increased with the duration of gestation after vaccination. Nevertheless, the antibody titers in both maternal and fetal blood were sufficient to afford protection against infection. Thus, efficient influenza vaccination can be undertaken at any stage of pregnancy. J. Med. Virol. 81:1923–1928, 2009. © 2009 Wiley‐Liss, Inc.     

Épidémie de grippe A(H1N1)2009 à La Réunion: expérience de la consultation ambulatoire dédiée, juillet–septembre 2009

From July 6 to September 29, 2009, 380 patients were seen as out-patients for flu-like illness, and 355 files (253 women and 102 men) were available for retrospective analysis. Mean age was 32 years. 158 patients, including 22 with A(H1N1)2009 influenza had underlying medical conditions: pregnancy (N = 87), asthma (N = 37), obesity (N = 17). Most frequent symptoms of A(H1N1)2009 influenza patients were fever (97% of the patients), cough (94%), rhinorrhea (59%), myalgia (56%), headache (36%). A nasopharyngeal swab for influenza virus detection by PCR was performed on 118 patients including 27 pregnant women. 44 patients, including 40 A(H1N1)2009 influenza cases were tested positive. 21 patients were referred to the emergency department for further tests or treatment and 31 patients were admitted as in-patients. 20 pregnant women were referred for further obstetrical monitoring; none presented with respiratory failure or foetal distress. None of the patients were admitted to the ICU or died.     

Classical swine H1N1 influenza viruses confer cross protection from swine-origin 2009 pandemic H1N1 influenza virus infection in mice and ferrets

The hemagglutinin of the 2009 pandemic H1N1 influenza virus is a derivative of and is antigenically related to classical swine but not to seasonal human H1N1 viruses. We compared the A/California/7/2009 (CA/7/09) virus recommended by the WHO as the reference virus for vaccine development, with two classical swine influenza viruses A/swine/Iowa/31 (sw/IA/31) and A/New Jersey/8/1976 (NJ/76) to establish the extent of immunologic cross-reactivity and cross-protection in animal models. Primary infection with 2009 pandemic or NJ/76 viruses elicited antibodies against the CA/7/09 virus and provided complete protection from challenge with this virus in ferrets; the response in mice was variable and conferred partial protection. Although ferrets infected with sw/IA/31 virus developed low titers of cross-neutralizing antibody, they were protected from pulmonary replication of the CA/7/09 virus. The data suggest that prior exposure to antigenically related H1N1 viruses of swine-origin provide some protective immunity against the 2009 pandemic H1N1 virus.     

Influenza M1 VLPs containing neuraminidase induce heterosubtypic cross-protection

Influenza virus like particles (VLPs) containing hemagglutinin were previously demonstrated to induce protection against the homologous strains. However, little information is available on the protective role of neuraminidase (NA), the second major glycoprotein. In this study, we developed VLPs (NA VLPs) containing NA and M1 derived from A/PR/8/34 (H1N1) influenza virus, and investigated their ability to induce protective immunity. Intranasal immunization with NA VLPs induced serum antibody responses to H1N1 and H3N2 influenza A viruses as well as significant neuraminidase inhibition activity. Importantly, mice immunized with NA VLPs were 100% protected against lethal infection by the homologous A/PR/8/34 (H1N1) as well as heterosubtypic A/Philippines/82 (H3N2) virus, although body weight loss was observed after lethal challenge with heterosubtypic H3N2 virus. The present study therefore provides evidence that influenza VLPs containing M1 and NA are capable of inducing immunity to homologous as well as antigenically distinct influenza A virus strains.     

Lower mannose‐binding lectin contributes to deleterious H1N1 2009 infection in children

Mannose‐binding lectin (MBL) has broad range of activity against viruses through the mechanisms of neutralization, opsonization, and complement activation. Prior studies have demonstrated that MBL inactivated the season's influenza virus. Due to the fact that children have no neutralizing antibody against H1N1 2009 virus, innate immunity may be crucial in the defense against influenza. Therefore, we studied whether MBL levels played a role in H1N1 2009 infection in children. In a prospective survey, we revealed that MBL levels in ICU influenza cases were significantly lower than in children with influenza from infection disease ward. MBL may be involved in innate immune responses to H1N1 2009 infection in children.     

Factors associated with severe disease in hospitalized adults with pandemic (H1N1) 2009 in Spain

The risk factors for complications in patients with influenza A (H1N1)v virus infection have not been fully elucidated. We performed an observational analysis of a prospective cohort of hospitalized adults with confirmed pandemic influenza A (H1N1)v virus infection at 13 hospitals in Spain, between June 12 and November 10, 2009, to identify factors associated with severe disease. Severe disease was defined as the composite outcome of intensive‐care unit (ICU) admission or in‐hospital mortality. During the study period, 585 adult patients (median age 40 years) required hospitalization because of pandemic (H1N1) 2009. At least one comorbid condition was present in 318 (54.4%) patients. Pneumonia was diagnosed in 234 (43.2%) patients and bacterial co‐infection in 45 (7.6%). Severe disease occurred in 75 (12.8%) patients, of whom 71 required ICU admission and 13 (2.2%) died. Independent factors for severe disease were age <50 years (OR, 2.39; 95% CI, 1.05–5.47), chronic comorbid conditions (OR, 2.93; 95% CI, 1.41–6.09), morbid obesity (OR, 6.7; 95% CI, 2.25–20.19), concomitant and secondary bacterial co‐infection (OR, 2.78; 95% CI, 1.11–7) and early oseltamivir therapy (OR, 0.32; 95% CI 0.16–0.63). In conclusion, although adults hospitalized for pandemic (H1N1) 2009 suffer from significant morbidity, mortality is lower than that reported in the earliest studies. Younger age, chronic comorbid conditions, morbid obesity and bacterial co‐infection are independent risk factors for severe disease, whereas early oseltamivir therapy is a protective factor.     

Long-Term Immunogenicity of an Inactivated Split-Virion 2009 Pandemic Influenza A H1N1 Virus Vaccine with or without Aluminum Adjuvant in Mice

In 2009, a global epidemic of influenza A(H1N1) virus caused the death of tens of thousands of people. Vaccination is the most effective means of controlling an epidemic of influenza and reducing the mortality rate. In this study, the long-term immunogenicity of influenza A/California/7/2009 (H1N1) split vaccine was observed as long as 15 months (450 days) after immunization in a mouse model. Female BALB/c mice were immunized intraperitoneally with different doses of aluminum-adjuvanted vaccine. The mice were challenged with a lethal dose (10× 50% lethal dose [LD₅₀]) of homologous virus 450 days after immunization. The results showed that the supplemented aluminum adjuvant not only effectively enhanced the protective effect of the vaccine but also reduced the immunizing dose of the vaccine. In addition, the aluminum adjuvant enhanced the IgG antibody level of mice immunized with the H1N1 split vaccine. The IgG level was correlated to the survival rate of the mice. Aluminum-adjuvanted inactivated split-virion 2009 pandemic influenza A H1N1 vaccine has good immunogenicity and provided long-term protection against lethal influenza virus challenge in mice.     

Humans and Ferrets with Prior H1N1 Influenza Virus Infections Do Not Exhibit Evidence of Original Antigenic Sin after Infection or Vaccination with the 2009 Pandemic H1N1 Influenza Virus

The hypothesis of original antigenic sin (OAS) states that the imprint established by an individual''s first influenza virus infection governs the antibody response thereafter. Subsequent influenza virus infection results in an antibody response against the original infecting virus and an impaired immune response against the newer influenza virus. The purpose of our study was to seek evidence of OAS after infection or vaccination with the 2009 pandemic H1N1 (2009 pH1N1) virus in ferrets and humans previously infected with H1N1 viruses with various antigenic distances from the 2009 pH1N1 virus, including viruses from 1935 through 1999. In ferrets, seasonal H1N1 priming did not diminish the antibody response to infection or vaccination with the 2009 pH1N1 virus, nor did it diminish the T-cell response, indicating the absence of OAS in seasonal H1N1 virus-primed ferrets. Analysis of paired samples of human serum taken before and after vaccination with a monovalent inactivated 2009 pH1N1 vaccine showed a significantly greater-fold rise in the titer of antibody against the 2009 pH1N1 virus than against H1N1 viruses that circulated during the childhood of each subject. Thus, prior experience with H1N1 viruses did not result in an impairment of the antibody response against the 2009 pH1N1 vaccine. Our data from ferrets and humans suggest that prior exposure to H1N1 viruses did not impair the immune response against the 2009 pH1N1 virus.     

Pandemic influenza A(H1N1)pdm09: risk of infection in primary healthcare workers

Background

Healthcare workers in primary care are at risk of infection during an influenza pandemic. The 2009 influenza pandemic provided an opportunity to assess this risk.

Aim

To measure the prevalence of seropositivity to influenza A(H1N1)pdm09 among primary healthcare workers in Canterbury, New Zealand, following the 2009 influenza pandemic, and to examine associations between seropositivity and participants’ sociodemographic characteristics, professional roles, work patterns, and seasonal influenza vaccination status.

Design and setting

An observational study involving a questionnaire and testing for influenza A(H1N1)pdm09 seropositivity in all primary healthcare workers in Canterbury, New Zealand between December 2009 and February 2010.

Method

Participants completed a questionnaire that recorded sociodemographic and professional data, symptoms of influenza-like illness, history of seasonal influenza vaccination, and work patterns. Serum samples were collected and haemagglutination inhibition antibody titres to influenza A(H1N1)pdm09 measured.

Results

Questionnaires and serum samples were received from 1027 participants, from a workforce of 1476 (response rate 70%). Seropositivity was detected in 224 participants (22%). Receipt of seasonal influenza vaccine (odds ratio [OR] = 2.0, 95% confidence interval [CI] = 1.2 to 3.3), recall of influenza (OR = 1.9, 95% CI = 1.3 to 2.8), and age ≤45 years (OR = 1.4, 95% CI = 1.0 to 1.9) were associated with seropositivity.

Conclusion

A total of 22% of primary care healthcare workers were seropositive. Younger participants, those who recalled having influenza, and those who had been vaccinated against seasonal influenza were more likely to be seropositive. Working in a dedicated influenza centre was not associated with an increased risk of seropositivity.     

Pandemic influenza A(H1N1) 2009 virus in pregnancy

Two hundred fourteen abstracts and 87 full texts regarding pregnant women infected with pandemic influenza A(H1N1) 2009 virus were systematically reviewed by using a PubMed search and assessing pandemic, clinical, laboratory test, vaccine, and control experiences. Both policy and health education were excluded. This review counted the total number of pregnant cases from different countries and analyzed their epidemic features, including trimester distribution, morbidity, hospitalization, intensive care unit admissions, maternal mortality, underlying diseases, complications, high‐risk factors for death, pregnancy outcome, and clinical symptoms compared with the previous pandemic seasonal influenza A/H1N1 as compared with the general population. Early identification and treatment were the most important factors in different countries and areas examined. The vaccine and antiviral drugs that have been the most efficient means to control the novel virus appear to be safe but require more extensive study. In the future, the focus should be placed on understanding vertical transmission and the severe mechanisms. Copyright © 2012 John Wiley & Sons, Ltd.     

Avian influenza virus in pregnancy

The unprecedented epizootic of avian influenza viruses, such as H5N1, H5N6, H7N1 and H10N8, has continued to cause disease in humans in recent years. In 2013, another novel influenza A (H7N9) virus emerged in China, and 30% of those patients died. Pregnant women are particularly susceptible to avian influenza and are more likely to develop severe complications and to die, especially when infection occurs in the middle and late trimesters. Viremia is believed to occur infrequently, and thus vertical transmission induced by avian influenza appears to be rare. However, avian influenza increases the risk of adverse pregnancy outcomes, including spontaneous abortion, preterm birth and fatal distress. This review summarises 39 cases of pregnant women and their fetuses from different countries dating back to 1997, including 11, 15 and 13 infections with H7N9, H5N1 and the 2009 pandemic influenza (H1N1), respectively. We analysed the epidemic features, following the geographical, population and pregnancy trimester distributions; underlying diseases; exposure history; medical timelines; human‐to‐human transmission; pathogenicity and vertical transmission; antivirus treatments; maternal severity and mortality and pregnancy outcome. The common experiences reported in different countries and areas suggest that early identification and treatment are imperative. In the future, vigilant virologic and epidemiologic surveillance systems should be developed to monitor avian influenza viruses during pregnancy. Furthermore, extensive study on the immune mechanisms should be conducted, as this will guide safe, rational immunomodulatory treatment among this high‐risk population. Most importantly, we should develop a universal avian influenza virus vaccine to prevent outbreaks of the different subtypes. Copyright © 2016 John Wiley & Sons, Ltd.     

广州市孕妇甲型H1N1流感疫苗接种意愿调查分析

目的了解广州市孕妇甲型H1N1流感疫苗接种意愿,为孕妇疫苗接种工作的开展及宣传教育提供依据。方法在广州市荔湾区、黄埔区、增城区按随机抽样的方法在门诊及住院部抽取孕产妇251人,问卷调查其对甲流疫苗接种的认识及意愿。结果有62.55%的孕妇表示如果免费接种本人愿意接种甲流疫苗,不同年龄段、不同户籍性质、不同文化程度孕妇接种意愿比较差异无统计学意义（P〉0.05）,分析不愿意接种的原因,有60.58%的孕妇是因为害怕影响胎儿健康,有46.22%的孕妇希望家人接种疫苗从而保护自身及胎儿不受感染。结论为防止孕妇感染甲型H1N1流感病毒,导致重症病例的出现,应加强孕产妇甲型H1N1流感疫苗接种的宣传教育,从而在疫苗接种阶段提高其接种率。     

Virus-like particle vaccine containing hemagglutinin confers protection against 2009 H1N1 pandemic influenza

Immunization of the world population before an influenza pandemic such as the 2009 H1N1 virus spreads globally is not possible with current vaccine production platforms. New influenza vaccine technologies, such as virus-like-particles (VLPs), offer a promising alternative. Here, we tested the immunogenicity and protective efficacy of a VLP vaccine containing hemagglutinin (HA) and M1 from the 2009 pandemic H1N1 influenza virus (H1N1pdm) in ferrets and compared intramuscular (i.m.) and intranasal (i.n.) routes of immunization. Vaccination of ferrets with VLPs containing the M1 and HA proteins from A/California/04/2009 (H1N1pdm) induced high antibody titers and conferred significant protection against virus challenge. VLP-vaccinated animals lost less weight, shed less virus in nasal washes, and had markedly lower virus titers in all organs tested than naïve controls. A single dose of VLPs, either i.m. or i.n., induced higher levels of antibody than did two doses of commercial split vaccine. Ferrets vaccinated with split vaccine were incompletely protected against challenge; these animals had lower virus titers in olfactory bulbs, tonsils, and intestines, but lost weight and shed virus in nasal washes to a similar extent as naïve controls. Challenge with heterologous A/Brisbane/59/07 (H1N1) virus revealed that the VLPs conferred minimal cross-protection to heterologous infection, as revealed by the lack of reduction in nasal wash and lung virus titers and slightly higher weight loss relative to controls. In summary, these experiments demonstrate the strong immunogenicity and protective efficacy of VLPs compared to the split vaccine and show that i.n. vaccination with VLPs has the potential for highly efficacious vaccination against influenza.     

Preexisting Antibody Response against 2009 Pandemic Influenza H1N1 Viruses in the Taiwanese Population

A novel pandemic influenza H1N1 (pH1N1) virus spread rapidly across the world in 2009. Due to the important role of antibody-mediated immunity in protection against influenza infection, we used an enzyme-linked immunosorbent assay-based microneutralization test to investigate cross-reactive neutralizing antibodies against the 2009 pH1N1 virus in 229 stored sera from donors born between 1917 and 2008 in Taiwan. The peak of cumulative geometric mean titers occurred in donors more than 90 years old and declined sharply with decreasing age. Sixteen of 27 subjects (59%) more than 80 years old had cross-reactive antibody titers of 160 or more against the 2009 pH1N1 virus, whereas none of the donors from age 9 to 49 had an antibody titer of 160 or more. Interestingly, 2 of 51 children (4%) from 6 months to 9 years old had an antibody titer of 40. We further tested the antibody responses in 9 of the 51 pediatric sera to three endemic seasonal influenza viruses isolated in 2006 and 2008 in Taiwan, and the results showed that only the 2 sera from children with antibody responses to the 2009 pH1N1 virus had high titers of neutralizing antibody against recent seasonal influenza virus strains. Our study shows the presence of some level of cross-reactive antibody in Taiwanese persons 50 years old or older, and the elderly subjects who may already have been exposed to the 1918 virus had high titers of neutralizing antibody to the 2009 pH1N1 virus. Our data also indicate that natural infection with the Taiwan 2006 and 2008 seasonal H1N1 viruses may induce a cross-reactive antibody response to the 2009 pH1N1 virus.Influenza A viruses have caused several pandemics during the past century and continue to cause epidemics around the world yearly. Pandemics are typically caused by the introduction of a virus with a hemagglutinin (HA) subtype that is new to human populations (14). In 2009, a novel pandemic influenza H1N1 (pH1N1) virus of swine origin spread rapidly and has caused variable disease globally via interhuman transmission (2, 3).The 2009 pH1N1 virus contains a unique combination of gene segments from both the North American and Eurasian swine lineages and is antigenically distinct from any known seasonal human influenza virus (14). Since H1N1 influenza A viruses have been circulating in human populations for decades, much of the world has encountered these viruses repeatedly, either through infection or through vaccination. Under the threat of a pandemic outbreak, however, a major concern is whether preexisting immunity can provide some protection from the novel 2009 pH1N1 virus.Recent reports from the United States suggested that 33% of individuals over the age of 60 years had neutralization antibodies to the novel 2009 pH1N1 virus, probably due to previous exposure to antigenically similar H1N1 viruses (1, 7). In Japan, however, appreciable neutralization antibodies against the 2009 pH1N1 virus were found only in individuals more than 90 years old (9). The differences in geographical location and vaccination programs against influenza in 1976 may account for the different age distributions of neutralization antibodies in the two countries. In the early 1900s, Taiwan had had a close relationship with Japan historically and geographically. The prevalence of influenza in Taiwan may be quite similar to that in Japan. In recent years, however, sequence analysis of epidemic influenza virus strains revealed that the Taiwanese strains usually circulate in Taiwan prior to their circulation in many other countries, including Japan. (16). The differences between the studies from United States and Japan, and the unique epidemic situation in Taiwan, highlight the need for us to assess the level of preexisting immunity in the Taiwanese population.In this study, we measured the titers of neutralizing antibodies against the 2009 pH1N1 virus in sera obtained from previous influenza infection or vaccination of different age groups. In addition, we also assessed the antibodies against the local seasonal H1N1 strains isolated in Taiwan in 2006 and 2008 (A/Taiwan/N86/06, A/Taiwan/N94/08, and A/Taiwan/N510/08) to evaluate whether there is a cross-reactive antibody response between recent local strains and the 2009 pH1N1 virus.