Evaluation of the antigenic relatedness and cross-protective immunity of the neuraminidase between human influenza A (H1N1) virus and highly pathogenic avian influenza A (H5N1) virus

AbstractTo determine the genetic and antigenic relatedness as well as the cross-protective immunity of human H1N1 and avian H5N1 influenza virus neuraminidase (NA), we immunized rabbits with either a baculovirus-expressed recombinant NA from A/Beijing/262/95 (BJ/262) H1N1 or A/Hong Kong/483/97 (HK/483) H5N1 virus. Cross-reactive antibody responses were evaluated by multiple serological assays and cross-protection against H5N1 virus challenge was evaluated in mice. In a neuraminidase inhibition (NI) test, the antisera exhibited substantial inhibition of NA activity of the homologous virus, but failed to inhibit the NA activity of heterologous virus. However, these antisera exhibited low levels of cross-reactivity measured by plaque size reduction, replication inhibition, single radial hemolysis, and ELISA assays. Passive immunization with HK/483 NA-specific antisera significantly reduced virus replication and disease, and afforded almost complete protection against lethal homologous virus challenge in mice. However, passive immunization with BJ/262 (H1N1) NA-specific antisera was ineffective at providing cross-protection against lethal H5N1 virus challenge and only slightly reduced weight loss. Substantial amino acid variation among the NA antigenic sites was observed between BJ/262 and HK/483 virus, which was consistent with the lack of cross-reactive NI activity by the antibody and limited cross-protective immunity in mice. These results show a strong correlation between the lack of cross-protective immunity and low structural similarities of NA from a human seasonal H1N1 virus and an avian H5N1 influenza virus

No Evidence of Avian Influenza A H5N1 among Returning US Travelers

We reviewed reports to the Centers for Disease Control and Prevention of US travelers suspected of having avian influenza A H5N1 virus infection from February 2003 through May 2006. Among the 59 reported patients, no evidence of H5N1 virus infection was found; none had had direct contact with poultry, but 42% had evidence of human influenza A

Leveraging International Influenza Surveillance Systems and Programs during the COVID-19 Pandemic.

A network of global respiratory disease surveillance systems and partnerships has been built over decades as a direct response to the persistent threat of seasonal, zoonotic, and pandemic influenza. These efforts have been spearheaded by the World Health Organization, country ministries of health, the US Centers for Disease Control and Prevention, nongovernmental organizations, academic groups, and others. During the COVID-19 pandemic, the US Centers for Disease Control and Prevention worked closely with ministries of health in partner countries and the World Health Organization to leverage influenza surveillance systems and programs to respond to SARS-CoV-2 transmission. Countries used existing surveillance systems for severe acute respiratory infection and influenza-like illness, respiratory virus laboratory resources, pandemic influenza preparedness plans, and ongoing population-based influenza studies to track, study, and respond to SARS-CoV-2 infections. The incorporation of COVID-19 surveillance into existing influenza sentinel surveillance systems can support continued global surveillance for respiratory viruses with pandemic potential

International laboratory comparison of influenza microneutralization assays for A(H1N1)pdm09, A(H3N2), and A(H5N1) influenza viruses by CONSISE

The microneutralization assay is commonly used to detect antibodies to influenza virus, and multiple protocols are used worldwide. These protocols differ in the incubation time of the assay as well as in the order of specific steps, and even within protocols there are often further adjustments in individual laboratories. The impact these protocol variations have on influenza serology data is unclear. Thus, a laboratory comparison of the 2-day enzyme-linked immunosorbent assay (ELISA) and 3-day hemagglutination (HA) microneutralization (MN) protocols, using A(H1N1)pdm09, A(H3N2), and A(H5N1) viruses, was performed by the CONSISE Laboratory Working Group. Individual laboratories performed both assay protocols, on multiple occasions, using different serum panels. Thirteen laboratories from around the world participated. Within each laboratory, serum sample titers for the different assay protocols were compared between assays to determine the sensitivity of each assay and were compared between replicates to assess the reproducibility of each protocol for each laboratory. There was good correlation of the results obtained using the two assay protocols in most laboratories, indicating that these assays may be interchangeable for detecting antibodies to the influenza A viruses included in this study. Importantly, participating laboratories have aligned their methodologies to the CONSISE consensus 2-day ELISA and 3-day HAMNassay protocols to enable better correlation of these assays in the future

Environmental Conditions Affect Exhalation of H3N2 Seasonal and Variant Influenza Viruses and Respiratory Droplet Transmission in Ferrets.

The seasonality of influenza virus infections in temperate climates and the role of environmental conditions like temperature and humidity in the transmission of influenza virus through the air are not well understood. Using ferrets housed at four different environmental conditions, we evaluated the respiratory droplet transmission of two influenza viruses (a seasonal H3N2 virus and an H3N2 variant virus, the etiologic virus of a swine to human summertime infection) and concurrently characterized the aerosol shedding profiles of infected animals. Comparisons were made among the different temperature and humidity conditions and between the two viruses to determine if the H3N2 variant virus exhibited enhanced capabilities that may have contributed to the infections occurring in the summer. We report here that although increased levels of H3N2 variant virus were found in ferret nasal wash and exhaled aerosol samples compared to the seasonal H3N2 virus, enhanced respiratory droplet transmission was not observed under any of the environmental settings. However, overall environmental conditions were shown to modulate the frequency of influenza virus transmission through the air. Transmission occurred most frequently at 23°C/30%RH, while the levels of infectious virus in aerosols exhaled by infected ferrets agree with these results. Improving our understanding of how environmental conditions affect influenza virus infectivity and transmission may reveal ways to better protect the public against influenza virus infections

Intranasal Vaccination with 1918 Influenza Virus-Like Particles Protects Mice and Ferrets from Lethal 1918 and H5N1 Influenza Virus Challenge▿

Influenza vaccines capable of inducing cross-reactive or heterotypic immunity could be an important first line of prevention against a novel subtype virus. Influenza virus-like particles (VLPs) displaying functional viral proteins are effective vaccines against replication-competent homologous virus, but their ability to induce heterotypic immunity has not been adequately tested. To measure VLP vaccine efficacy against a known influenza pandemic virus, recombinant VLPs were generated from structural proteins of the 1918 H1N1 virus. Mucosal and traditional parenteral administrations of H1N1 VLPs were compared for the ability to protect against the reconstructed 1918 virus and a highly pathogenic avian H5N1 virus isolated from a fatal human case. Mice that received two intranasal immunizations of H1N1 VLPs were largely protected against a lethal challenge with both the 1918 virus and the H5N1 virus. In contrast, mice that received two intramuscular immunizations of 1918 VLPs were only protected against a homologous virus challenge. Mucosal vaccination of mice with 1918 VLPs induced higher levels of cross-reactive immunoglobulin G (IgG) and IgA antibodies than did parenteral vaccination. Similarly, ferrets mucosally vaccinated with 1918 VLPs completely survived a lethal challenge with the H5N1 virus, while only a 50% survival rate was observed in parenterally vaccinated animals. These results suggest a strategy of VLP vaccination against a pandemic virus and one that stimulates heterotypic immunity against an influenza virus strain with threatening pandemic potential

Impact of Immunosuppression on Recall Immune Responses to Influenza Vaccination in Stable Renal Transplant Recipients

BackgroundThe recommendation by the American Society of Transplantation for annual trivalent inactivated influenza vaccination greater than 3 to 6 months post-kidney transplantation provides a unique opportunity to test the in vivo impact of immunosuppression on recall T- and B-cell responses to influenza vaccination.MethodsThis study took advantage of recent breakthroughs in the single-cell quantification of human peripheral blood B-cell responses to prospectively evaluate both B- and T-cell responses to the seasonal (2010 and 2011) influenza vaccine in 23 stable renal transplant recipients and 22 healthy controls.Results and conclusionThe results demonstrate that the early B-cell response to influenza vaccination, quantified by the frequency of influenza-specific antibody-secreting cells (ASC) in peripheral blood, was significantly reduced in stable transplant recipients compared to healthy controls. The magnitude of the seroresponse and the rate of seroconversion were also blunted. The influenza-specific interferon-gamma (IFNγ) T-cell response was significantly reduced in transplant recipients; however, there was no correlation between the magnitude of the influenza-specific IgG ASC and IFNγ responses. The induction of memory T- and B-cell responses to influenza vaccination supports the recommendation to vaccinate while the blunted responses demonstrate the efficacy of immunosuppression in controlling memory responses individual transplant recipients

Recovery rates of influenza virus subjected to the aerosol collection procedure.

<p>Prepared impactor plates were spiked with 10²–10³ pfu of PN99 (green) or IN11 (orange) influenza virus and were placed at a designated environmental condition as shown on the x-axis while air was pulled through them for 15 minutes (A) or 5 minutes (B). Experiments were performed in duplicate and the percentage of recovered RNA was determined by real time RT-PCR using M gene primers and infectious virus recovery was based on plaque assays. Each shaded section represents the proportion of the total amount of input virus that was recovered.</p

Volume of aerosols exhaled by naïve and influenza virus inoculated ferrets.

<p>Aerosol volumes were measured from ferrets during 15 minutes of normal breathing (NB) or 5 minutes of sneezing stimulation (SZ). Data collected from naïve animals, n = 6 (A), and data collected from inoculated animals (normalized to each ferret’s naïve level of aerosol shedding), n = 3, on 2, 4 and 6 dpi were combined and compared between PN99 and IN11 virus groups for aerosols <5 μm and ≥5 μm (B,C). Ferrets were housed under controlled environmental conditions as indicated. Data are presented + standard deviation.</p

Influenza virus in aerosol samples exhaled by infected ferrets based on recovery rates.

<p>Three ferrets each were housed under the designated environmental conditions and were presented with 10^3.8–10^5.5 pfu of PN99 (green) or IN11 (orange) virus by aerosol inhalation. Aerosol samples were collected from ferrets on 1, 3, and 5 dpi for 15 minutes of normal breathing (A) and 5 minutes of sneezing stimulation (B). Total plaque forming units (pfu) collected from infected ferrets were normalized based on the recovery rates of known amounts of infectious virus using our aerosol collection procedure. Total pfu exhaled by infected ferrets in both size ranges combined and at each time point are presented. Each dot represents a single animal at a single time point. Scatter dot plots show the distribution of data with the horizontal line representing the grand mean for all samples collected under the designated condition.</p