Comparison of long-term systemic and secretory antibody responses in children given live, attenuated, or inactivated influenza A vaccine

A comparison of inactivated intramuscular and live intranasal influenza A vaccines in young children undergoing primary immunization might be expected to show differences in serum and local mucosal antibody responses. To demonstrate such differences, serum and local respiratory tract antibody responses of young children vaccinated with intranasal live, attenuated, cold-adapted (H3N2 or H1N1), or intramuscular inactivated (H3N2) influenza A vaccines were examined for one year after vaccination. Antibody responses were measured by hemagglutination-inhibition (HAI) and class-specific enzyme-linked immunosorbent assay (ELISA). One year after vaccination, live intranasal vaccinees had significantly less decay of serum HAI (p = 0.025) and IgG antibody (p = 0.01) directed against the influenza hemagglutinin and neuraminidase than did intramuscular inactivated vaccinees. Nasal secretory IgA developed almost exclusively in live vaccinees and persisted for up to one year. Persistent nasal secretory IgG was detected in both live and inactivated vaccinees. Live vaccination not only stimulates a more durable serum antibody response, but also induces long-lasting local respiratory tract IgA antibody that may play an important role in host protection.     

In elderly persons live attenuated influenza A virus vaccines do not offer an advantage over inactivated virus vaccine in inducing serum or secretory antibodies or local immunologic memory.

In a double-blind, randomized trial, 102 healthy elderly subjects were inoculated with one of four preparations: (i) intranasal bivalent live attenuated influenza vaccine containing cold-adapted A/Kawasaki/86 (H1N1) and cold-adapted A/Bethesda/85 (H3N2) viruses; (ii) parenteral trivalent inactivated subvirion vaccine containing A/Taiwan/86 (H1N1), A/Leningrad/86 (H3N2), and B/Ann Arbor/86 antigens; (iii) both vaccines; or (iv) placebo. To determine whether local or systemic immunization augmented mucosal immunologic memory, all volunteers were challenged intranasally 12 weeks later with the inactivated virus vaccine. We used a hemagglutination inhibition assay to measure antibodies in sera and a kinetic enzyme-linked immunosorbent assay to measure immunoglobulin G (IgG) and IgA antibodies in sera and nasal washes, respectively. In comparison with the live virus vaccine, the inactivated virus vaccine elicited higher and more frequent rises of serum antibodies, while nasal wash antibody responses were similar. The vaccine combination induced serum and local antibodies slightly more often than the inactivated vaccine alone did. Coadministration of live influenza A virus vaccine did not alter the serum antibody response to the influenza B virus component of the inactivated vaccine. The anamnestic nasal antibody response elicited by intranasal inactivated virus challenge did not differ in the live, inactivated, or combined vaccine groups from that observed in the placebo group not previously immunized. These results suggest that in elderly persons cold-adapted influenza A virus vaccines offer little advantage over inactivated virus vaccines in terms of inducing serum or secretory antibody or local immunological memory. Studies are needed to determine whether both vaccines in combination are more efficacious than inactivated vaccine alone in people in this age group.     

Influenza virus NS vectors expressing the mycobacterium tuberculosis ESAT-6 protein induce CD4+ Th1 immune response and protect animals against tuberculosis challenge

Infection with Mycobacterium tuberculosis remains a major cause of morbidity and mortality all over the world. Since the effectiveness of the only available tuberculosis vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is suboptimal, there is a strong demand to develop new tuberculosis vaccines. As tuberculosis is an airborne disease, the intranasal route of vaccination might be preferable. Live influenza virus vaccines might be considered as potential vectors for mucosal immunization against various viral or bacterial pathogens, including M. tuberculosis. We generated several subtypes of attenuated recombinant influenza A viruses expressing the 6-kDa early secretory antigenic target protein (ESAT-6) of M. tuberculosis from the NS1 reading frame. We were able to demonstrate the potency of influenza virus NS vectors to induce an M. tuberculosis-specific Th1 immune response in mice. Moreover, intranasal immunization of mice and guinea pigs with such vectors induced protection against mycobacterial challenge, similar to that induced by BCG vaccination.     

Asthma, influenza, and vaccination

Exacerbations of asthma in children are usually triggered by virus infections. Many different respiratory viruses are associated with these exacerbations, but influenza viruses are frequently associated with those requiring hospitalization and are the only ones for which specific treatment and prophylaxis are available. Current studies have shown that influenza vaccines are safe for patients with asthma. The efficacy of inactivated influenza vaccines in preventing exacerbations of asthma has been questioned. The live attenuated influenza vaccine has been licensed recently in the United States, and studies have shown it to be safe and protective. A direct comparison of the inactivated and live attenuated influenza vaccines in children with asthma demonstrated superior protection by the latter. Live attenuated influenza vaccine, given by nasal spray, is better accepted by children for annual vaccination and is easier to administer. Universal vaccination of all children in school-based clinics will facilitate control of epidemic influenza and provide an infrastructure for control of future influenza pandemics.     

Vaccination against acute respiratory virus infections and measles in man.

Several viruses may cause more or less severe acute respiratory infections in man, some of which are followed by systemic infection. Only for influenza and measles are licensed vaccines available at present. The protection induced by influenza vaccines, which are based on inactivated whole virus or viral subunits, depends largely on the matching of vaccine strain and circulating virus. Measles vaccines, which are based on attenuated live virus, have been quite effective in controlling the disease in vaccinated populations in the industrialized world. In developing countries, severe measles infections occur in infants from six to nine months of age, which necessitates the vaccination of children of less than six months. At that time maternal antibodies, that may interfere with the induction of protection, may still be present. Therefore, instead of using the parenteral route, the possibility to use the mucosal route of primary immunization is also investigated for vaccination with attenuated live measles vaccines. The use of inactivated measles vaccines has resulted in a state of immunity which upon exposure to the virus may induce an atypical measles syndrome including a severe pneumonia. Measles virus proteins presented in an iscom matrix have recently been shown to induce functional B and T cell responses to both the surface glycoproteins of the virus. These responses could also be induced in the presence of virus neutralizing antibodies and they proved to be protective in several animal model systems. Many of the problems that have been encountered in the development of measles vaccines, proved to be similar in the development of vaccines against other paramyxoviruses causing acute respiratory infections in man, including respiratory syncytial virus. Parenteral application of inactivated and attenuated live vaccines against these paramyxoviruses has generally had little success. Topical application of attenuated live vaccines has been more successful, and also the use of vaccinia recombinant viruses expressing foreign paramyxoviral glycoproteins has shown promising results in laboratory animals. Live vaccines based on adenovirus types 4 and 7 in oral enteric-coated vaccines, which lead to virus replication in the intestines but not in the respiratory tract have been included in military vaccination programs. The possibility to replace e.g. the E3 region with foreign DNA makes adenoviruses also suitable as cloning vectors for proteins of other respiratory viruses. Although live attenuated vaccines against some of the serotypes of rhinoviruses have shown promising results, the generation of a multivalent vaccine against this epidemiologically most significant cause of acute respiratory infections will be almost impossible, due to the multiplicity of serotypes involved.(ABSTRACT TRUNCATED AT 400 WORDS)     

Live cold-adapted reassortant influenza vaccines]

The author reviews studies of live cold-adapted reassortant influenza vaccines developed in Russia and USA. These vaccines are safe and weakly reactogenic for all age groups. The vaccines (two immunizations) are highly effective in children of preschool and school age and far less effective in adults. For elderly subjects simultaneous vaccination with live and inactivated vaccines is recommended. The probability of influenza prevention by a single injection of cold-adapted vaccines is to be further investigated. Modern data indicate that cold-adapted reassortant influenza vaccines can be used for influenza prevention only in children of preschool and school age.     

Proteosome-adjuvanted intranasal influenza vaccines: advantages, progress and future considerations

The development of a safe and effective non-live intranasal influenza vaccine has been an elusive target in vaccinology for many decades. It is perceived that intranasal immunization, by offering a more convenient and less invasive vaccination modality, will boost vaccination rates against influenza, a disease that continues to inflict a significant annual health and economic burden worldwide. Intranasal immunization may also confer additional immunoprotective benefits by eliciting mucosal secretory antibodies at the site of entry of the virus, which are typically more broadly cross-reactive and cross-protective compared with those induced by systemic routes of vaccination. This property is highly desirable for confering improved protection against variant strains of influenza virus. Here we review the current status of intranasal proteosome-based influenza vaccines that comprise commercial detergent-split influenza antigens and proteosome adjuvants derived from purified bacterial outer membrane proteins. We demonstrate that these vaccines exhibit the desired advantages expected from immunization via the intranasal route. Furthermore, in clinical trials proteosome-based influenza vaccines were shown to be safe and protective in humans. The future possibilities for commercializing intranasal proteosome-influenza vaccines are also discussed.     

Comparison of inactivated, live and recombinant DNA vaccines against influenza virus in a mouse model

The protective efficacy of influenza hemagglutinin expressed from recombinant vaccinia virus was compared with that induced by inactivated or infectious influenza vaccines. Intraperitoneal and intranasal routes of vaccination were compared. All the vaccines except the intranasally administered, inactivated vaccine induced detectable levels of neutralizing and hemagglutination-inhibiting antibodies in the serum of mice at 28 days postvaccination. Immunization with any of the intranasally administered vaccines reduced the amount of influenza virus nucleoprotein antigen in lungs after challenge with a homologous, mouse-adapted strain of influenza virus. Intraperitoneally administered vaccines failed to provide such protection. These results indicated that the route of vaccine administration may be the most critical factor for inducing protective immunity. The results also showed that in this mouse model a recombinant DNA-based vaccine could provide protection equivalent to that provided by conventional attenuated and inactivated influenza vaccines.     

Prophylaxis and Treatment of Influenza Virus Infection

Influenza virus infections remain an important cause of morbidity and mortality. Furthermore, a recurrence of pandemic influenza remains a real possibility. There are now effective ways to both prevent and treat influenza. Prevention of infection is most effectively accomplished by vaccination. Vaccination with the inactivated, intramuscular influenza vaccine has been clearly demonstrated to reduce serious morbidity and mortality associated with influenza infection, especially in groups of patients at high risk (e.g. the elderly). However, the inactivated, intramuscular vaccine does not strongly induce cell-mediated or mucosal immune responses, and protection induced by the vaccine is highly strain specific. Live, attenuated influenza vaccines administered intranasally have been studied in clinical trials and shown to elicit stronger mucosal and cell-mediated immune responses. Live, attenuated vaccines appear to be more effective for inducing protective immunity in children or the elderly than inactivated, intramuscular vaccines. Additionally, novel vaccine methodologies employing conserved com-ponents of influenza virus or viral DNA are being developed. Preclinical studies suggest that these approaches may lead to methods of vaccination that could induce immunity against diverse strains or subtypes of influenza. Because of the limitations of vaccination, antiviral therapy continues to play an important role in the control of influenza. Two major classes of antivirais have demonstrated ability to prevent or treat influenza in clinical trials: the adaman-tanes and the neuraminidase inhibitors. The adamantanes (amantadine and rimantadine) have been in use for many years. They inhibit viral uncoating by blocking the proton channel activity of the influenza A viral M2 protein. Limitations of the adamantanes include lack of activity against influenza B, toxicity (especially in the elderly), and the rapid development of resistance. The neuraminidase inhibitors were designed to interfere with the conserved sialic acid binding site of the viral neuraminidase and act against both influenza A and B with a high degree of specificity when administered by the oral (oseltamivir) or inhaled (zanamivir) route. The neuraminidase inhibitors have relatively low toxicity, and viral resistance to these inhibitors appears to be uncommon. Additional novel antivirals that target other phases of the life cycle of influenza are in preclinical development. For example, recombinant collectins inhibit replication of influenza by binding to the viral haemagglutinin as well as altering phagocyte responses to the virus. Recombinant techniques have been used for generation of antiviral proteins (e.g. modified collectins) or oligonucleotides. Greater understanding of the biology of influenza viruses has already resulted in significant advances in the management of this important pathogen. Further advances in vaccination and antiviral therapy of influenza should remain a high priority.     

Microneedle and mucosal delivery of influenza vaccines

In recent years with the threat of pandemic influenza and other public health needs, alternative vaccination methods other than intramuscular immunization have received great attention. The skin and mucosal surfaces are attractive sites probably because of both noninvasive access to the vaccine delivery and unique immunological responses. Intradermal vaccines using a microinjection system (BD Soluvia(TM)) and intranasal vaccines (FluMist?) are licensed. As a new vaccination method, solid microneedles have been developed using a simple device that may be suitable for self-administration. Because coated microneedle influenza vaccines are administered in the solid state, developing formulations maintaining the stability of influenza vaccines is an important issue to be considered. Marketable microneedle devices and clinical trials remain to be developed. Other alternative mucosal routes such as oral and intranasal delivery systems are also attractive for inducing cross-protective mucosal immunity, but effective non-live mucosal vaccines remain to be developed.     

Influenza Vaccination and Asthma

Influenza is an important epidemic and pandemic illness associated with serious morbidity and mortality in unprotected communities. Patients at increased risk of infection are those with pre-existing cardiopulmonary disease including asthma. The influenza virus has the ability to produce antigenic changes posing problems for vaccine development. Influenza vaccines have been available for over 50 years. Despite the continuing global threat posed by infection and recommendations in many countries that immunisation should be widely given, uptake rates are variable and often poor. It has been demonstrated that infection with influenza and other respiratory viral pathogens can produce exacerbations of asthma throughout the age groups. Despite this, vaccine uptake rates in asthmatic populations are quite low. Poor uptake rates are attributed to a number of factors and we review the evidence for the widely held view that influenza vaccination produces exacerbations of chronic airflow obstruction including asthma. Observational studies have found conflicting results: some post immunisation changes in bronchial hyperreactivity and increased requirements of bronchodilator therapy have been in some, but not all, studies. Placebo-controlled trials have not demonstrated any clinical deterioration although one study showed a small reduction in peak expiratory flow rate. Intranasal administration of cold-adapted live vaccines and new nucleic acid vaccines are briefly considered. Live adapted vaccines have been shown to be effective in influenza immunoprophylaxis and limited data on their use in patients with asthma suggest that they can be administered safely. In conclusion, based up on current studies and evidence, it seems likely that influenza infection produces morbidity in patients with asthma but that any potential adverse effects of influenza immunisation are outweighed by the benefits in this population. However, placebo-controlled trials are few and only small numbers of asthmatic patients have been investigated.     

Induction of cross‐protective immunity against influenza A virus H5N1 by an intranasal vaccine with extracts of mushroom mycelia

The identification of a safe and effective adjuvant that is able to enhance mucosal immune responses is necessary for the development of an efficient inactivated intranasal influenza vaccine. The present study demonstrated the effectiveness of extracts of mycelia derived from edible mushrooms as adjuvants for intranasal influenza vaccine. The adjuvant effect of extracts of mycelia was examined by intranasal co‐administration of the extracts and inactivated A/PR8 (H1N1) influenza virus hemagglutinin (HA) vaccine in BALB/c mice. The inactivated vaccine in combination with mycelial extracts induced a high anti‐A/PR8 HA‐specific IgA and IgG response in nasal washings and serum, respectively. Virus‐specific cytotoxic T‐lymphocyte responses were also induced by administration of the vaccine with extract of mycelia, resulting in protection against lethal lung infection with influenza virus A/PR8. In addition, intranasal administration of NIBRG14 vaccine derived from the influenza A/Vietnam/1194/2004 (H5N1) virus strain administered in conjunction with mycelial extracts from Phellinus linteus conferred cross‐protection against heterologous influenza A/Indonesia/6/2005 virus challenge in the nasal infection model. In addition, mycelial extracts induced proinflammatory cytokines and CD40 expression in bone marrow‐derived dendritic cells. These results suggest that mycelial extract‐adjuvanted vaccines can confer cross‐protection against variant H5N1 influenza viruses. The use of extracts of mycelia derived from edible mushrooms is proposed as a new safe and effective mucosal adjuvant for use for nasal vaccination against influenza virus infection. J. Med. Virol. 82:128–137, 2010. © 2009 Wiley‐Liss, Inc.     

Humoral and cellular immune responses of seronegative children vaccinated with a cold-adapted influenza A/HK/123/77 (H1N1) recombinant virus.

Humoral and cell-mediated immune responses of young, seronegative children were assessed after intranasal vaccination with a cold-adapted influenza. A/HK/77 (H1N1) CR 35 recombinant virus. Vaccines shedding influenza virus experienced a rise in hemagglutinin-inhibition antibody 15 to 30 days after vaccination. Vaccinees showed low but significant lymphocyte transformation to A/USSR (H1N1) by day 8 after vaccination, which decreased to prevaccination levels at 30 to 34 days. The lymphocyte transformation response occurred before serum antibody rises were detected by hemagglutinin-inhibition assay. No change in lymphocyte responsiveness was observed after vaccination as measured by phytohemagglutinin stimulation. Lymphocytes responded to in vitro incubation with inactivated influenza (H1N1) virus by producing interferon. The interferon produced was of type I and was observed in vaccinees and nonvaccinees both before and after vaccination.     

Influenza virus: immunity and vaccination strategies. Comparison of the immune response to inactivated and live, attenuated influenza vaccines

Influenza virus is a globally important respiratory pathogen which causes a high degree of morbidity and mortality annually. The virus is continuously undergoing antigenic change and thus bypasses the host's acquired immunity to influenza. Despite the improvement in antiviral therapy during the last decade, vaccination is still the most effective method of prophylaxis. Vaccination induces a good degree of protection (60-90% efficacy) and is well tolerated by the recipient. For those at risk of complications from influenza, annual vaccination is recommended due to the antigenic changes in circulating strains. However, there is still room for improvement in vaccine efficacy, long-lasting effect, ease of administration and compliance rates. The mucosal tissues of the respiratory tract are the main portal entry of influenza, and the mucosal immune system provides the first line of defence against infection. Secretory immunoglobulin A (SIgA) and IgM are the major neutralizing antibodies directed against mucosal pathogens. These antibodies work to prevent pathogen entry and can function intracellularly to inhibit replication of virus. This review describes influenza virus infection, epidemiology, clinical presentation and immune system response, particularly as it pertains to mucosal immunity and vaccine use. Specifically, this review provides an update of the current status on influenza vaccination and concentrates on the two main types of influenza vaccines currently in use, namely the cold-adapted vaccine (CAV) given intranasally/orally, and the inactivated vaccine (IV) delivered subcutanously or intramuscularly. The commercially available trivalent IV (TIV) elicits good serum antibody responses but induces poorly mucosal IgA antibody and cell-mediated immunity. In contrast, the CAV may elicit a long-lasting, broader immune (humoral and cellular) response, which more closely resembles natural immunity. The immune response induced by these two vaccines will be compared in this review.     

The immune response to influenza vaccines

Specific immunity to influenza is associated with a systemic immune response (serum haemagglutination inhibition antibody), local respiratory immune response (virus-specific local IgA and IgG antibodies in nasal wash), and with the cell-mediated immune response. Both inactivated and live influenza vaccines induce virus-specific serum antibody which can protect against infection with influenza virus possessing the same antigenic specificity. In the absence of serum antibodies, local antibodies in nasal wash are a major determinant of resistance to infection with influenza virus. In comparative studies in humans it was shown that nasal secretory IgA develops chiefly after immunization with live cold-adapted (CA) vaccine, but persistent nasal secretory IgG was detected in both CA live and inactivated vaccines. The origin of nasal wash haemagglutination inhibition (HI) antibodies is not completely known. Recently it was found that cytotoxic T-cells (CTL) play an important role in immunity against influenza and in clearance of influenza virus from the body. In primed humans, inactivated influenza vaccine stimulates a cross-reactive T-cell response, whereas the ability of inactivated vaccine to stimulate such immunity in unprimed humans has not been determined. Data on the T-cell response to live vaccine in humans are limited to the development of secondary T-cell responses in primed individuals vaccinated with a host-range (HR) attenuated vaccine. The data obtained have shown that immunity induced by inactivated influenza vaccines is presumably dependent on the stimulation of serum antibody. Live CA vaccines not only stimulate a durable serum antibody response, but also induce long-lasting local respiratory tract IgA antibody that plays an important role in host protection.     

Infant rat model of attenuation for recombinant influenza viruses prepared from cold-adapted attenuated A/Ann Arbor/6/60.

The pathogenicity of 6 wild-type influenza A viruses and 21 recombinant strains prepared from wild-type viruses and cold-adapted A/Ann Arbor/6/60 virus for infant rats was determined. Thus, the titers of virus present in the turbinates and lungs of virus-infected animals was measured serially for 5 days after intranasal infection, and the ability of virus strains to promote subsequent systemic bacterial infection by Haemophilus influenzae was measured at 48 h after virus infection. The results obtained were assessed with reference to the genetic constitution of the virus strains and to virus virulence for volunteers. The results showed that virulent viruses grew to relatively high titers in rat turbinates and significantly promoted systemic infection by H. influenzae. In contrast, attenuated strains grew to lower titers and failed to promote systemic H. influenzae infection. For the strains tested, the results showed clear differences for attenuated and virulent strains, and the model was a reliable indication of virulence for humans. Although the virulent strains tended to grow to higher titers in rat lungs than did attenuated strains, exceptions were found, and this measurement could not reliably discriminate virulent and attenuated virus strains. The results suggest that infant rats can be used to assess the virulence of cold-adapted recombinant influenza virus strains, and thus, they can facilitate the development of such strains for vaccine production.     

The mucosal vaccine quandary: intranasal vs. sublingual immunization against influenza

Intranasal vaccination can effectively induce both local and systemic immune responses and protect against influenza, but poses a risk of antigen or adjuvant delivery into the central nervous system (CNS). Sublingual vaccine delivery has recently received increased attention as a safer alternative to the intranasal route. Studies comparing the two routes have found that higher immune responses may be induced by intranasal than sublingual administration, possibly as a consequence of the differences in mucosal tissues between the two routes. Here we examine evidence of antigen transport into the CNS following intranasal immunisation and discuss possible reasons for the superiority of the intranasal as compared with the sublingual route in terms of vaccine immunogenicity. We encourage generation of more information on the safety of mucosal adjuvants and propose that the next generation of vaccines and adjuvants may be designed specifically for administration via the different mucosal routes.     

Growth of influenza A viruses in hamsters

Summary The growth characteristics of four temperature-sensitive or cold-adapted recombinant influenza viruses and eight recombinant influenza viruses derived in other ways, together with the wild-type, parent viruses of these strains, were tested in hamster lungs and turbinates and in embryonated eggs at different temperatures for their replicative ability. The results showed that although the temperature-sensitive and cold-adapted recombinant viruses replicated to considerably lower titres than their wild-type parent virus strains in hamster lung and at 37° C in embryonated eggs, no similar pattern of growth was observed for the group of A/PR8 and A/Okuda recombinant influenza viruses studied in these systems. The hamster model is not therefore generally applicable as a marker for attenuated influenza virus vaccine strains.With 1 Figure     

New aspects of influenza viruses.

Influenza virus infections continue to cause substantial morbidity and mortality with a worldwide social and economic impact. The past five years have seen dramatic advances in our understanding of viral replication, evolution, and antigenic variation. Genetic analyses have clarified relationships between human and animal influenza virus strains, demonstrating the potential for the appearance of new pandemic reassortants as hemagglutinin and neuraminidase genes are exchanged in an intermediate host. Clinical trials of candidate live attenuated influenza virus vaccines have shown the cold-adapted reassortants to be a promising alternative to the currently available inactivated virus preparations. Modern molecular techniques have allowed serious consideration of new approaches to the development of antiviral agents and vaccines as the functions of the viral genes and proteins are further elucidated. The development of techniques whereby the genes of influenza viruses can be specifically altered to investigate those functions will undoubtedly accelerate the pace at which our knowledge expands.     

Intranasal Immunization of Mice with Inactivated Virus and Mast Cell Activator C48/80 Elicits Protective Immunity against Influenza H1 but not H5

Vaccination represents the most economic and effective strategy of preventing influenza pandemics. We previously demonstrated that intranasal immunization of mice with recombinant hemagglutinin and the mast cell activator C48/80 elicited protective immunity against challenge with the 2009 pandemic H1N1 influenza in mice, demonstrating that the novel C48/80 mucosal adjuvant was safe and effective. The present study demonstrated that intranasal immunization with inactivated H1N1 virus and C48/80 elicited protective immunity against lethal challenge with homologous virus, however, when the immunogen was replaced with inactivated H5N1 virus protection was lost. These observations suggested that the adjuvant effects conferred by C48/80 were virus subtype specific and that its use as a broad-spectrum adjuvant for use in immunizations against all influenza viruses needs to be further analyzed.