Protective effects of nasal immunization in mice with various kinds of inactivated Sendai virus vaccines

The immunoprophylactic effects of nasal vaccination with 13 different kinds of inactivated Sendai virus vaccines were compared by contact exposure to infector mice. Efficacies of the vaccines were evaluated on the basis of the presence of virus-infected cells by immunofluorescent examination of the entire respiratory tract, including the nasal mucosa. A single or double inoculations of B-propiolactone (0.5%)-vaccine promoted the infection in the respiratory tract, particularly in the nasal mucosa, whereas three inoculations of B-propiolactone (0.2%)-vaccine provided considerable protection throughout the respiratory tract with only slight development of serum HI titer. Formalin (0.1%)-vaccine and UV irradiated-vaccine strongly protected the nasal mucosa from infection, but did not sufficiently safeguard the lower respiratory tract even with three vaccinations despite adequate development of serum antibody. Nearly complete protection of the entire respiratory tract was induced with six to eight inoculations of a vaccine treated excessively with both UV rays and 1% formalin, without significant development of serum antibody. Out of eight thermal vaccines, five (inactivated at 23 C, 30 C, 37 C and 7 C, and 30 C and 7 C) provided strong protection against infection when inoculated three times. The others inactivated at higher temperatures (37 C, 50 C, or 60 C) were not so protective. High serum HI titers developed, on the whole, with the drop in the temperature required for inactivating the virus. In eight immune mouse groups in which infection was strongly suppressed in the entire respiratory tract, most of the mice harbored less than 50 viral antigen-positive cells in their nasal mucosa in the postexposure period. The number of the cells was assumed to be a useful criterion for evaluation of vaccine efficacy.     

Further Search for Small Molecular Inactivants Capable of Eliciting Respiratory Mucosal Immunogenicity by Modifying Sendai Virus Core RNA

Five groups of 32 chemicals were examined regarding their immunological functions as modifier inactivants to make inactivated Sendai nasal vaccine using a contact exposure experiment, direct immunofluorescent method, and serum HI titer. (1) Five of the nine reactive groups of reactive dyes (2-chloropyridine, 2, 4, 6-trichloropyrimidine, vinylsulfonic acid, epichlorohydrin and beta-chloroethylamine) induced complete or almost complete defense in the entire respiratory tract, and the four other vaccines brought about slight infection in the respiratory tracts. There was no marked rise in serum HI titers post-exposure, despite uneven development. (2) Of the four sizable substituted AS naphthol vaccines, naphthol AS-IRG and AS-G vaccines elicited nearly complete defense, but the two other vaccines, inactivated with more elongated molecules, invited rare and successive infections. The three immune groups produced invariably high serum HI titers. (3) Of the six naphthalene derivative vaccines, two (3-hydroxy-2-naphthoic acid methylester and 2-naphthol-6-sulfonic acid) induced complete or almost complete protection. But two vaccines brought about less protection, and the remaining two vaccines caused heavy infections. (4) Of the six benzene derivative vaccines, both m-nitrobenzenesulfonic acid and isatoic anhydride induced complete protection. Three vaccines permitted slight infections but 2, 4, 6-trinitrobenzenesulfonic acid vaccine caused severe infection. (5) Of the seven food dye vaccines, only orange I induced complete or nearly complete defense, while the other dye vaccines were inferior. In effect, twelve inactivated Sendai nasal vaccines modified the ribose and/or phosphate groups of the virus core RNA through five groups of small-sized molecules with specially fixed side chains, and elicited complete or almost complete respiratory mucosal defense. The viral stabilization requiring the least alteration of the configuration will be involved in the chemical modification.     

Inactivated Rabies Vaccine Produced from the Flury LEP Strain of Virus Grown in BHK-21 Suspension Cells

Suspension cultures of BHK-21 cells maintained at 32 to 33 C were infected with the Flury LEP strain of rabies virus. By using a cell concentration of 2.0 x 10(6) to 2.5 x 10(6) cells per ml infected at a multiplicity of 0.05, high titers of extracellular virus were reached in 96 to 120 h, and potent inactivated vaccines were prepared from culture fluids harvested between 96 to 168 h. The addition of 1% bovine serum to the maintenance medium resulted in an increase in virus yields and vaccine potency. Estimation of the number of infected cells by immunofluorescent procedures proved a rapid and reliable guide to the virus content of suspension cultures.     

Inducement of Respiratory Mucosal Immunogenicity for Nasal Vaccine Due to Amine- and Amide-Inactivation of Parainfluenza Virus Type 1, Sendai

The protective effects in mice by nasal vaccination of amine- and amide-inactivated Sendai viruses were investigated by a contact exposure experiment, immunofluorescent examination of the entire respiratory tract, and checking the serum HI antibody development. Of 10 monoamines, ethanolamine and 2-methoxyethylamine vaccines induced complete protection, and methylamine, ethylamine, n-propylamine, n-butylamine, 2-ethoxyethylamine, diethylamine and triethylamine vaccines brought about almost complete protection or lower respiratory infection. The methoxyamine-treated mouse conferred the least protection. Of 5 diamines, 1, 3-diaminopropane vaccine inhibited completely the infection, but hydrazine, ethylenediamine, putrescine, and cadaverine vaccines produced regional infection. Two polyamines, spermine and spermidine, did not inactivate the virus. Of 4 amides, only semicarbazide vaccine conferred complete mucosal defense, while acetamide, propionamide, and isonicotinic acid hydrazide vaccines lead to regional infection. Serum HI titers developed by vaccination were low on the whole, following their slight rise, fall or maintenance postexposure. In effect, the 4 vaccines inactivated by a best-suited interstrand crosslink between phosphate groups in helix of viral RNA brought about the strongest protection, and showed the necessity of a definite length of molecules for inactivants.     

Gamma-Irradiated Venezuelan Equine Encephalitis Vaccines

The efficacy of Formalin-inactivated Venezuelan equine encephalitis (VEE) vaccine has been reported to be low for man. Although a live VEE vaccine has been shown to be highly effective for the protection of laboratory workers, local and systemic reactions have occurred in approximately 20% of inoculated individuals. Therefore, studies were initiated in an attempt to produce an inactivated vaccine of high potency with low toxicity. Inactivated VEE vaccines were prepared by exposing virus suspensions to 8 x 10(6) or 10 x 10(6) r of gamma radiation. Irradiated VEE vaccines prepared from virus suspensions produced in Maitland-type chick embryo (MTCE) cell cultures and in monolayer cultures of human diploid strain WI-38 cells were highly immunogenic for mice and guinea pigs. Guinea pigs vaccinated with a series of three inoculations of vaccine (MTCE) survived challenge with at least 10(8.4) mouse intracerebral 50% lethal doses of VEE virus. Irradiated vaccines induced high levels of serum-neutralizing and hemagglutinin-inhibiting antibodies in guinea pigs and rabbits. These findings suggest that ionizing radiation may be effective in the preparation of an inactivated VEE vaccine.     

Experimental Sendai virus infection in laboratory rats. II. Pathology and immunohistochemistry

Intranasal inoculation of 5 to 8 week old specific pathogen-free Sprague-Dawley rats with 5 X 10(3) egg infectious doses of Sendai virus resulted in severe rhinitis, bronchiolitis and alveolitis. The most severe rhinitis occurred on postinoculation (PI) days 4-6, and pneumonia on day 4. Rhinitis and pneumonia persisted to PI day 21, with peribronchial lymphoid infiltration detectable at PI day 42. Immunohistochemical studies showed that Sendai virus antigens were present primarily in columnar epithelial cells of the respiratory mucosa of the nasal cavity and in bronchiolar and alveolar epithelium. Antigen was first detectable at PI day 1, was most prominent at days 3-4 and was undetectable after day 7. More antigen could be seen in the nasal mucosa than in the lung at any stage in the infection. These studies show that Sendai virus by itself is capable of evoking severe, although transient, rhinitis and pneumonia in laboratory rats free of other significant pathogens.     

Co-immunization with West Nile DNA and inactivated vaccines provides synergistic increases in their immunogenicities in mice

West Nile virus is now distributed throughout many temperate, subtropical and tropical areas: vaccines need to be developed that are affordable for developed and developing countries. Here, we constructed and evaluated a DNA vaccine expressing the premembrane and envelope proteins of West Nile virus (pcWNME). Mice immunized twice with 100 or 10 microg of pcWNME developed high or moderate levels of neutralizing antibodies, respectively. These mice were protected from viremia and death after lethal challenge. Mice immunized with a mixture of 1 microg of pcWNME and a small amount (1/10 dose) of a commercial inactivated vaccine developed moderate levels of neutralizing antibodies, whereas immunization with pcWNME or the inactivated vaccine alone induced only low or undetectable levels: co-immunization with the DNA and protein vaccines synergistically increased their own immunogenicities. The synergism reduced the amount of DNA sufficient to induce neutralizing antibodies: a single immunization with doses as low as 0.1 microg induced a titer of 1:40 at a 90% plaque reduction 6 or 9 weeks after immunization. Both IgG1 and IgG2a antibodies were induced in mice by co-immunization with the DNA and protein vaccines.     

Human immune responses elicited by an intranasal inactivated H5 influenza vaccine

Intranasally administered influenza vaccines could be more effective than injected vaccines, because intranasal vaccination can induce virus-specific immunoglobulin A (IgA) antibodies in the upper respiratory tract, which is the initial site of infection. In this study, immune responses elicited by an intranasal inactivated vaccine of influenza A(H5N1) virus were evaluated in healthy individuals naive for influenza A(H5N1) virus. Three doses of intranasal inactivated whole-virion H5 influenza vaccine induced strong neutralizing nasal IgA and serum IgG antibodies. In addition, a mucoadhesive excipient, carboxy vinyl polymer, had a notable impact on the induction of nasal IgA antibody responses but not on serum IgG antibody responses. The nasal hemagglutinin (HA)-specific IgA antibody responses clearly correlated with mucosal neutralizing antibody responses, indicating that measurement of nasal HA-specific IgA titers could be used as a surrogate for the mucosal antibody response. Furthermore, increased numbers of plasma cells and vaccine antigen-specific Th cells in the peripheral blood were observed after vaccination, suggesting that peripheral blood biomarkers may also be used to evaluate the intranasal vaccine-induced immune response. However, peripheral blood immune cell responses correlated with neutralizing antibody titers in serum samples but not in nasal wash samples. Thus, analysis of the peripheral blood immune response could be a surrogate for the systemic immune response to intranasal vaccination but not for the mucosal immune response. The current study suggests the clinical potential of intranasal inactivated vaccines against influenza A(H5N1) viruses and highlights the need to develop novel means to evaluate intranasal vaccine-induced mucosal immune responses.     

Standardization of an enzyme immunoassay for the in vitro potency assay of inactivated tissue culture rabies vaccines: determination of the rabies virus glycoprotein with polyclonal antisera

A non-competitive enzyme-linked immunoassay (ELISA) has been standardized to supplement the in vivo potency test used for the quality control of inactivated tissue culture vaccines against rabies. The essentials of the ELISA were: fixation of the virus in different dilutions of vaccine on the surface of microtitre plates; testing of the reference and up to six test vaccines on one plate; incubation with polyclonal antisera to rabies virus glycoprotein containing an excess of antibody; further incubation with a species-specific anti-IgG coupled to peroxidase; a final incubation with a substrate. The incubation periods were 1 h, 1 h and 30 min both at +37 degrees C. The relative potency determinations were made graphically or by a computer using a parallel line bioassay in which the potencies of the vaccines of unknown potency were tested against the reference preparation on a single microtitre plate. Under these conditions inactivated rabies vaccines of different types (virus strains, cell substrates, inactivation and concentration procedures) were tested for potency. Furthermore, it was possible with this in vitro method to assay adjuvanted vaccines, in process samples such as tissue culture supernatants with live or inactivated rabies virus, concentrates, and vaccines undergoing thermal stability tests. The rabies glycoprotein antigen-antibody reaction was highly specific according to the results and the glycoprotein content was measured quantitatively. The potency determined by the in vitro ELISA correlated with the in vivo NIH protection potency test. The lower limit of detection of the ELISA was 0.015 IU/ml. Quantitative antigen determination was possible with both homologous and heterologous antisera to rabies virus glycoprotein when vaccines of the same virus strain were tested. When the potencies of vaccines of different virus strain specificity were calculated, it was necessary to take into account the strain-specific antigenicity. Even so vaccines of high potency were found to give a stronger reaction with a heterologous serum than did weak vaccines with a homologous antiserum. Stability tests made on inactivated tissue culture vaccines such as vaccine from the human diploid cell strain (HDCS), from purified chicken embryo cell (PCEC) or from purified Vero cell rabies vaccine (PVRV), showed high stability of the glycoprotein antigen even after four months of storage at +37 degrees C or 24 h at +56 degrees C, provided that the vaccines were stored in a lyophilized state. The antigenicity of liquid vaccines was inactivated after a few hours at +56 degrees C. For tropical areas, therefore, only lyophilized vaccines should be considered.     

Evaluation of the potential use of inactivated influenza centrifuged vaccines with various hemagglutinin levels for immunizing schoolchildren

The safety, reactogenic properties and immunogenic potency of inactivated influenza centrifuged vaccines with different hemagglutinin content were studied in observations on children aged 11-15 and 7-10 years. According to the results of clinico-laboratory investigations, commercial influenza vaccine and its variant with hemagglutinin content reduced by half were found to be safe and showed faintly pronounced reactogenic properties in children. After vaccination hyperemia developed at the site of injection, moderate in 5% of the vaccinees aged 7-10 years and mild in other vaccinees of both age groups. The immunogenic potency of the preparations was determined by the specific features of influenza virus strains: strain A (H1N1) induced seroconversion in 62-94% and strain A (H3N2), in 67-96% of children.     

Endocine?, N3OA and N3OASq; Three Mucosal Adjuvants That Enhance the Immune Response to Nasal Influenza Vaccination

Annual outbreaks of seasonal influenza are controlled or prevented through vaccination in many countries. The seasonal vaccines used are either inactivated, currently administered parenterally, or live-attenuated given intranasally. In this study three mucosal adjuvants were examined for the influence on the humoral (mucosal and systemic) and cellular influenza A-specific immune responses induced by a nasally administered vaccine. We investigated in detail how the anionic Endocine™ and the cationic adjuvants N3OA and N3OASq mixed with a split inactivated influenza vaccine induced influenza A-specific immune responses as compared to the vaccine alone after intranasal immunization. The study showed that nasal administration of a split virus vaccine together with Endocine™ or N3OA induced significantly higher humoral and cell-mediated immune responses than the non-adjuvanted vaccine. N3OASq only significantly increased the cell-mediated immune response. Furthermore, nasal administration of the influenza vaccine in combination with any of the adjuvants; Endocine™, N3OA or N3OASq, significantly enhanced the mucosal immunity against influenza HA protein. Thus the addition of these mucosal adjuvants leads to enhanced immunity in the most relevant tissues, the upper respiratory tract and the systemic circulation. Nasal influenza vaccination with an inactivated split vaccine can therefore provide an important mucosal immune response, which is often low or absent after traditional parenteral vaccination.     

A Novel Bivalent Vaccine Based on a PB2-Knockout Influenza Virus Protects Mice from Pandemic H1N1 and Highly Pathogenic H5N1 Virus Challenges

Vaccination is an effective means to protect against influenza virus. Although inactivated and live-attenuated vaccines are currently available, each vaccine has disadvantages (e.g., immunogenicity and safety issues). To overcome these problems, we previously developed a replication-incompetent PB2-knockout (PB2-KO) influenza virus that replicates only in PB2 protein-expressing cells. Here, we generated two PB2-KO viruses whose PB2-coding regions were replaced with the HA genes of either A/California/04/2009 (H1N1pdm09) or A/Vietnam/1203/2004 (H5N1). The resultant viruses comparably, or in some cases more efficiently, induced virus-specific antibodies in the serum, nasal wash, and bronchoalveolar lavage fluid of mice relative to a conventional formalin-inactivated vaccine. Furthermore, mice immunized with these PB2-KO viruses were protected from lethal challenges with not only the backbone virus strain but also strains from which their foreign HAs originated, indicating that PB2-KO viruses with antigenically different HAs could serve as bivalent influenza vaccines.     

Cross-protection against influenza virus infection afforded by trivalent inactivated vaccines inoculated intranasally with cholera toxin B subunit.

Cross-protection against influenza virus infection was examined in mice, immunized intranasally with a nasal site-restricted volume of inactivated vaccines together with cholera toxin B subunit (CTB) as an adjuvant. The mice were challenged with either a small or a large volume of mouse-adapted virus suspension, each of which gave virgin mice either a predominant upper or lower respiratory tract infection. A single dose of a monovalent influenza A H3N2 virus vaccine with CTB provided complete cross-protection against the small-volume challenge with a drift virus within the same subtype, but a slight cross-protection against the large-volume challenge. A second dose of another drift virus vaccine increased the efficacy of cross-protection against the large-volume challenge. Similar cross-protection against H1N1, H3N2, or B type drift virus challenge was provided in the mice having received a primary dose of a mixture of H1N1, H3N2, and B virus vaccines with CTB and a second dose of another trivalent vaccine. The degree of cross-protection against the small- and the large-volume infection paralleled mainly the amount of cross-reacting IgA antibodies to challenge virus hemagglutinin in the nasal wash and that of cross-reacting IgG antibodies in the bronchoalveolar wash, respectively. On the other hand, in mice immunized subcutaneously with the trivalent vaccines having no cross-reacting IgA antibodies, the efficacy of cross-protection was not so high as that of nasal vaccination. These results suggest that the nasal inoculation of trivalent vaccines with CTB provides cross-protection against a broader range of viruses than does the current parenteral vaccination.     

Vaccination of macaques with adjuvanted formalin-inactivated influenza A virus (H5N1) vaccines: protection against H5N1 challenge without disease enhancement

We investigated the ability of adjuvanted, inactivated split-virion influenza A virus (H5N1) vaccines to protect against infection and demonstrated that the disease exacerbation phenomenon seen with adjuvanted formaldehyde-inactivated respiratory syncytial virus and measles virus investigational vaccines did not occur with these H5N1 vaccines. Macaques were vaccinated twice with or without an aluminum hydroxide or oil-in-water emulsion adjuvanted vaccine. Three months later, animals were challenged with homologous wild-type H5N1. No signs of vaccine-induced disease exacerbation were seen. With either adjuvant, vaccination induced functional and cross-reactive antibodies and protected the lungs and upper respiratory tract. Without an adjuvant, the vaccine provided partial protection. Best results were obtained with the emulsion adjuvant.     

Do we need nasal vaccines against COVID 19 to suppress the transmission of infections?

Covid-19 vaccines have within the first year prevented about 14 million deaths but did not induce a strong mucosal immune response. Data from US, UK, Singapore and Israel showed a variable and mostly modest effects of vaccination on virus excretion during breakthrough infections. Contact studies showed decreased transmission of infection from vaccinated index cases, but the effect varied according to dominant virus type, with study type and the nature of the contact group and diminished with time after vaccination. Some researchers suspect that it is unlikely to stop the pandemic with injected vaccines alone. Promising animal experiments were conducted with mucosal vaccines. Mice nasally immunized with a chimpanzee adenovirus vector mounted a mucosal immune response, were protected against viral challenge after a single vaccine dose and suppressed nasal replication of the challenge virus. Phage T4 expressing SARS-CoV-2 spike and nucleocapsid induced a sterilizing lung immunity in nasally vaccinated mice. Also hamsters intranasally immunized with the prefusion-stabilized spike protein showed no infectious virus in nasal turbinates upon challenge. Other studies showed that intranasal vaccination with an adenovirus vaccine reduced but did not eliminated viral transmission from infected to naïve hamsters. Intranasal vaccination of rhesus macaques with adenovirus vaccines also substantially reduced or even suppressed viral replication in the upper and lower respiratory tract. Human data on mucosal SARS-CoV-2 vaccines are so far limited to safety and immunogenicity studies. Aerosolized adenovirus vaccines given either as a booster or as primary immunization were safe and induced similar or superior immune response than injected vaccines while an aerosolized influenza vectored vaccine induced only a weak humoral and cellular immune response. Overall 100 mucosal SARS-CoV-2 vaccines are in development and 20 are in clinical trials. First human trials demonstrate that this will not be an easy task.     

Functional Differences of Dyes in Inducing Respiratory Immunogenicity by Azo-, Thiazole-, Quinoline-, Reactive-, and Naphthol-Dye-Inactivated Sendai Viruses

The prophylactic effects by mouse nasal inoculation of 31 kinds of organic dye-inactivated Sendai viruses were investigated by contact exposure experiment that used mouse nasally infected with 10^5,8 EID₅₀, immunofluorescent examination of the entire respiratory tract, and check of rise of serum HI titer postexposure. The relative merits of the dye-structures for inciting nasal immunogenicity were determined. Of 14 azo-dye-inactivated vaccines, only azo blue- and amido black 10B treated ones brought about nearly complete protection, while the other 5 dye-groups provided partial protection and the remaining 7 dye-groups the least protection. Of 6 thiazole dye-vaccines, primuline-, thioflavine S-, and thioflavine T-vaccines induced complete or almost complete protection, and the others moderate or the least protection. With 3 quinolinevaccines, both pinacyanol- and quinaldine red-inactivated ones provided complete protection, but not with quinoline blue-vaccine. Of 4 reactive dye-vaccines, both cibacron brilliant yellow 3G-P-and reactive blue 4-treated ones brought about nearly complete protection, but the remaining 2 vaccines induced regional infection. Nevertheless, all 4 naphthol group (AS, AS-BS, AS-BI, and AS-MX)-treated vaccines yielded complete or almost complete protection. The thirteen most effective vaccine groups suppressed marked rise of high or low serum HI titers developed through nasal vaccination postexposure. In short, specified dyestuffs having a great affinity for cellulosic fibers, evidently incited mucosal immunogenicity, probably by major union of the dyes to viral core ribose.     

Antibody responses to two encephalomyocarditis virus vaccines in rhesus macaques (Macaca mulatta)

Abstract: Two groups of rhesus macaques (Macaca mulatta) housed in rodent-controlled outdoor corrals were inoculated with two different encephalomyocarditis virus (EMCV) vaccines. One group (n = 45) received a vaccine made from an inactivated field isolate of virus cultured during an outbreak at a zoo in Florida. This vaccine produced fourfold increases in the titers of 28 animals (62%); the increases persisted for at least 18 months (last test) after a single injection of the vaccine. The other group (n = 51) received a vaccine made from an inactivated porcine field strain of the virus. This vaccine did not produce titers in any of the vaccinees.     

汉滩病毒84Fli株DNA疫苗诱导小鼠免疫应答的初步研究

为了加强我国病毒性出血热的防治,本研究将汉滩病毒84Fli株核蛋白S和糖蛋白M编码片段分别克隆至pcDNA3.0载体,构建了pcDNA3/84S和pcDNA3/84M重组质粒,等量混合采用肌肉注射途径免疫C57BL/6小鼠,免疫3次,每次间隔2周,同时与双价出血热病毒灭活疫苗进行对比。ELISA及免疫荧光(IFA)分别检测小鼠血清中汉滩病毒核蛋白及糖蛋白特异性抗体,流式细胞仪和ELISPOT方法分析小鼠免疫后的细胞免疫水平。微量中和试验检测小鼠血清抗体的的中和活性。结果显示,DNA疫苗免疫组C57BL/6小鼠在初次免疫2周后即能检测到汉滩病毒核蛋白与糖蛋白的特异性抗体,与灭活疫苗组相比,重组质粒诱导的抗体滴度高,产生时间早,产生的抗体具有中和活性;同时可诱导产生特异性细胞免疫应答。研究表明,汉滩病毒pcDNA3/84S和pcDNA3/84M重组质粒能有效刺激小鼠产生特异性体液免疫和细胞免疫应答。     

Immunogenicity of Live Attenuated B. pertussis BPZE1 Producing the Universal Influenza Vaccine Candidate M2e

Background

Intranasal delivery of vaccines directed against respiratory pathogens is an attractive alternative to parenteral administration. However, using this delivery route for inactivated vaccines usually requires the use of potent mucosal adjuvants, and no such adjuvant has yet been approved for human use.

Methodology/Principal Findings

We have developed a live attenuated Bordetella pertussis vaccine, called BPZE1, and show here that it can be used to present the universal influenza virus epitope M2e to the mouse respiratory tract to prime for protective immunity against viral challenge. Three copies of M2e were genetically fused to the N-terminal domain of filamentous hemagglutinin (FHA) and produced in recombinant BPZE1 derivatives in the presence or absence of endogenous full-length FHA. Only in the absence of FHA intranasal administration of the recombinant BPZE1 derivative induced antibody responses to M2e and effectively primed BALB/c mice for protection against influenza virus-induced mortality and reduced the viral load after challenge. Strong M2e-specific antibody responses and protection were observed after a single nasal administration with the recombinant BPZE1 derivative, followed by a single administration of M2e linked to a virus-like particle without adjuvant, whereas priming alone with the vaccine strain did not protect.

Conclusions/Significance

Using recombinant FHA-3M2e-producing BPZE1 derivatives for priming and the universal influenza M2e peptide linked to virus-like particles for boosting may constitute a promising approach for needle-free and adjuvant-free nasal vaccination against influenza.