Killed Influenza Virus Research Articles

Sustained release of inactivated H1N1 virus from degradable microparticles for extended vaccination

Influenza vaccines administered as intramuscularly injected inactivated viruses or intranasally administered live-attenuated viruses usually provide short-term protection against influenza infections. Biodegradable particles that provide sustained release of the antigen has been studied as an approach to extend vaccine protection. Here, we investigate sustained release of ultraviolet killed influenza A virus (A/PR/8/34(H1N1)) (kPR8) loaded into poly(D,L-lactic-co-glycolic acid) (PLGA) microparticles. Particles were prepared using the double emulsion method, and polymer molecular weight (MW), polymer hydrophobicity, polymer concentration in the organic phase, and the amount of killed virus were varied to obtain a range of particles. Formulations included PLGA 50:50 (2–6, 7–17 kDa), PLGA 75:25 (4–15 kDa), and 50/50 PLGA 75:25 (4–15 kDa)/PCL (14 kDa). Additionally, NaOH was co-encapsulated in some cases to enhance particle degradation. The structure of the particles was explored by size measurements and electron microscopy. The kPR8 release profiles were measured using hemagglutinin ELISA. The concentration of the polymer (PLGA) in the organic phase and polymer MW significantly influenced virus loading, while polymer MW and co-encapsulation of NaOH modulated the release profiles. Mice receiving a single intramuscular injection of NaOH microparticle-encapsulated kPR8 were partially protected against a lethal influenza challenge 32 weeks post immunization. Microparticle (MP) vaccination induced a gradual increase in PR8-specific IgGs dominated by IgG1 in contrast to the rapid IgG2a-biased response elicited by soluble kPR8 immunization. Our results indicate that vaccine-NaOH co-loaded PLGA particles show potential as a single dose vaccination strategy for extended protection against influenza virus infection.

Sustained release system from PLGA particles co-encapsulated with inactivated influenza virus with natural killer T cell agonist α-galactosylceramide

Vaccines against influenza and many other infectious diseases require multiple boosters in addition to the primary dose to improve efficacy, but this approach is not ideal for compliance. The multiple doses could potentially be replaced by sustained or pulsatile release of antigens encapsulated in degradable microparticles (MPs). The efficacy of a vaccine is improved by adding an adjuvant, which can be co-delivered from the particles to enhance immunogenicity. Here, we developed degradable poly-lactic-co-glycolic acid (PLGA) (7–17 kDa) MPs capable of sustained release of ultraviolet killed influenza virus (A/PR/8/34) (kPR8) vaccine and the natural killer T (NKT) cell agonist alpha-galactosylceramide (α-GalCer) and tested their effectiveness at providing long-term protection against influenza virus infection in mice. Multiple formulations were developed for encapsulating the virus and adjuvant separately, and in combination. The MPs exhibited sustained release of both the virus and the adjuvant lasting more than a month. Co-encapsulation significantly increased the encapsulation efficiency (EE) of the vaccine but reduced the release duration. On the other hand, co-encapsulation led to a reduction in EE for the α-GalCer and a change in release profile to a higher initial burst followed by a linear release compared to a low initial burst and slower linear release. The α-GalCer also had considerably longer release duration compared to the vaccine. Mice injected with particle formulations co-encapsulating kPR8 and α-GalCer were protected from a lethal influenza virus infection 30 weeks after vaccination. This study demonstrates that PLGA MP based vaccines are promising for providing effective vaccination and possibly for replacing multiple doses with a single injection.

Immunization with live influenza virus induces greater polyfunctional CD4+ T cell response compared to inactivated virus

Previous work has shown that infection of dendritic cells with influenza virus results in more diverse and efficient antigen presentation on MHC-II compared to treatment with excess doses of killed influenza virus. Accordingly, immunization of mice with live influenza virus elicits a greater frequency and breadth of CD4+ T cells than killed virus, as determined by interferon (IFN)-gamma ELISpot. Here, we sought to more fully characterize the differences in CD4+ T cell functionality induced by live vs. killed virus vaccines. C57Bl/6 mice were immunized with live influenza virus A/Puerto Rico/8/1934 (PR8) or a large excess dose of inactivated PR8. Efforts were made to control for the antigen load and adjuvant effects. Influenza-specific CD4+ T cells were evaluated by peptide/MHC-II tetramer staining, intracellular cytokine staining after peptide restimulation, and flow cytometry. Greater frequencies of PR8-specific CD4+ T cells were elicited by live vs. killed virus, as measured by tetramer staining or expression of the cytokines IFN-gamma, TNF, or IL-2. Of particular note, live virus induced a significantly higher frequency of polyfunctional CD4+ T cells, producing two or more cytokines when stimulated with peptide. This result was evident when polyfunctional CD4+ T cells were expressed as a fraction of all CD4+ T cells or PR8 epitope-specific CD4+ T cells. The difference in polyfunctional CD4+ T cells was maintained when antigenically distinct influenza virus B/Lee/1940 was mixed with killed PR8 as an adjuvant or when killed PR8 was administered in a prime/boost series. The data are consistent with a model whereby endogenous antigen presentation on MHC-II transmits more potent activating signals to CD4+ T cells than exogenous presentation, leading to a greater level of type 1 helper cytokine production and potentially greater antiviral effects.

Influenza Vaccination of Swine Reduces Public Health Risk at the Swine-Human Interface.

ABSTRACTInfluenza A viruses (IAV) in swine (IAV-S) pose serious risk to public health through spillover at the human-animal interface. Continued zoonotic transmission increases the likelihood novel IAV-S capable of causing the next influenza pandemic will emerge from this animal reservoir. Because current mitigation strategies are insufficient to prevent IAV zoonosis, we investigated the ability of swine vaccination to decrease IAV-S zoonotic transmission risk. We assessed postchallenge viral shedding in market-age swine vaccinated with either live-attenuated influenza virus (LAIV), killed influenza virus (KV), or sham vaccine (NV). We also assessed postchallenge transmission by exposing naive ferrets to pigs with contact types reflective of those experienced by humans in a field setting. LAIV and KV swine groups exhibited a nearly 100-fold reduction in peak nasal titer (LAIV mean, 4.55 log 50% tissue culture infectious dose [TCID50]/ml; KV mean, 4.53 log TCID50/ml) compared to NV swine (mean, 6.40 log TCID50/ml). Air sampling during the postchallenge period revealed decreased cumulative IAV in LAIV and KV study room air (LAIV, area under the concentration-time curve [AUC] of 57.55; KV, AUC = 24.29) compared to the NV study room (AUC = 86.92). Pairwise survival analysis revealed a significant delay in onset of infection among ferrets exposed to LAIV pigs versus NV pigs (rate ratio, 0.66; P = 0.028). Ferrets exposed to vaccinated pigs had lower cumulative virus titers in nasal wash samples (LAIV versus NV, P < 0.0001; KV versus NV, P= 0.3490) and experienced reduced clinical signs during infection. Our findings support the implementation of preexhibition influenza vaccination of swine to reduce the public health risk posed by IAV-S at agricultural exhibitions.IMPORTANCE Swine exhibited at agricultural fairs in North America have been the source of repeated zoonotic influenza A virus transmission, which creates a pathway for influenza pandemic emergence. We investigated the effect of using either live-attenuated influenza virus or killed influenza virus vaccines as prefair influenza vaccination of swine on zoonotic influenza transmission risk. Ferrets were exposed to the pigs in order to simulate human exposure in a field setting. We observed reductions in influenza A virus shedding in both groups of vaccinated pigs as well as the corresponding ferret exposure groups, indicating vaccination improved outcomes on both sides of the interface. There was also significant delay in onset of infection among ferrets that were exposed to live-attenuated virus-vaccinated pigs, which might be beneficial during longer fairs. Our findings indicate that policies mandating influenza vaccination of swine before fairs, while not currently common, would reduce the public health risk posed by influenza zoonosis.

Immune responses to killed reassorted influenza virus supplemented with natural adjuvants.

In this study, we investigated the immunomodulatory effects of a supplemented killed influenza virus (V) by Echinacea purpurea (E) and Nigella sativa (N) extracts and effect of changing the route of immunization from intramuscular (IM) to intraperitoneal (IP). At the 2nd-, 3rd- and 4th-week post-IM immunizations (WPIMI), the supplemented V with N (VN) induced the most significant IgM response unlike N alone. At the 2nd WPIMI, V or VN induced the highest significant IgG levels. At the 2nd-week post-IP immunization (WPIPI), E and VN induced the most significant IgG levels. Both at the 3rd and 4th WPIMI or WPIPI, various treatments induced significant increases in IgG. At the 4th WPIMI, E, V, and V with E (VE) induced significant increases in the CD4+ thymocytes while all IP treatments caused significant increase in their counts. V and VN induced the most significant IM induction of CD8+ thymocytes while their best IP stimulation was induced by N, VE, and VN. At the 4th WPIMI, various treatments caused significant increases in the mesenteric lymph node (MLN) CD4+, CD8+ counts. WPIPI with V or VE caused significant increases in both the CD4+- and CD8+ MLN cells, whereas VN significantly induced CD8+ MLN cells only. WPIPI with various treatments caused significant increases in the B-cell counts and the peak was obtained by VN.

An elastase-dependent attenuated heterologous swine influenza virus protects against pandemic H1N1 2009 influenza challenge in swine

Influenza virus infections continue to cause production losses in the agricultural industry in addition to being a human public health concern. The primary method to control influenza is through vaccination. However, currently used killed influenza virus vaccines must be closely matched to the challenge virus. The ability of an elastase-dependent live attenuated influenza A virus was evaluated to protect pigs against the pandemic H1N1 2009 influenza virus. Pigs vaccinated intranasally or intratracheally with the elastase-dependent swine influenza virus (SIV) vaccine had significantly reduced macroscopic and microscopic lung lesions and lower viral loads in the lung and in nasal swabs. Thus, elastase-dependent SIV mutants can be used as live-virus vaccines against swine influenza in pigs. In addition, low levels of cross-neutralizing antibodies to H1N1 2009 were elicited prior to challenge by the swine adapted H1N1 avian strain vaccine.

Influenza vaccine in children with asthma: Why no progress?

In an average year, 20% to 30% of chil- dren will be infected with influenza; this attack rate may be substantially higher during epidemic years and among certain populations, such as children in day care. Although most regard influenza as a self-limited ill- ness in children, it may cause substan- tial morbidity in children with and fluenza-associated excess hospitaliza- tion rates of 3 per 1000 high-risk chil- dren younger than 4 years. 2 For the vast majority of these children, the high-risk condition was asthma. Simi- larly, we conducted a study of children with asthma enrolled in Tennessee Medicaid and demonstrated excess hospitalization rates of 5.6 per 1000 children with asthma aged 1 to 3 years. 3 The hospitalization rates in both of these studies are comparable to rates in adult high-risk populations for whom influenza vaccine is recom- mended. In addition, in the Tennessee Medicaid study, an estimated 10% to 20% of children with asthma younger than 15 years had an additional outpa- tient visit during an average influenza season, and approximately 14% of such children received an additional antibiotic prescription. 3

Interferon-gamma production in response to in vitro stimulation with collagen type II in rheumatoid arthritis is associated with HLA-DRB1(*)0401 and HLA-DQ8.

IFN-γ was measured in supernatants after in vitro stimulation of peripheral blood mononuclear cells with collagen type II (CII), purified protein derivative or influenza virus. IFN-γ production in response to CII was similar in rheumatoid arthritis (RA) patients and healthy control individuals. The IFN-γ response to purified protein derivative and influenza virus was lower in RA patients, reflecting a general T-cell hyporesponsiveness in RA. After recalculating the response to CII taking this hyporesponsiveness into account the CII response was higher in RA patients, and was associated with human leucocyte antigen (HLA)-DRB1*0401 and HLA-DQA1*0301-DQB1*0302 (HLA-DQ8). Rheumatoid arthritis patients with elevated serum levels of immunoglobulin (Ig)G anti-CII antibodies had lower CII-induced IFN-γ production than patients with low anti-CII levels. The relative increase in CII-reactivity in RA patients as compared with healthy control individuals, and the association of a higher response with RA-associated HLA haplotypes, suggest the existence of a potentially pathogenic cellular reactivity against CII in RA.

Serum Antibody Response to Influenza Vaccine in Pulmonary Patients Receiving Corticosteroids

Despite the recommendation that patients with chronic lung diseases--many of whom receive corticosteroids--receive annual influenza vaccination, it is not known whether corticosteroids influence antibody response to influenza vaccine in this population. The purpose of this study was to assess whether patients with pulmonary conditions receiving long-term corticosteroid therapy develop an adequate antibody response. We prospectively studied 39 consecutive candidates for influenza vaccination, 25 of whom were receiving corticosteroids for underlying lung diseases. Patients with immunosuppression besides corticosteroids were excluded. Serum samples were obtained prior to and 1 month after vaccination with inactivated trivalent influenza vaccine and assayed for antibodies to the three strains using a hemagglutination inhibition assay. No patients had any intercurrent illness compatible with influenza during the study period and patients receiving corticosteroids continued treatment with them during this time. A fourfold rise in antibody titer at 1 month to at least one component was seen in 21 of 25 (84%) of corticosteroid-treated patients, which was similar to patients not receiving corticosteroids (11/14, 79%). There was no corticosteroid-antibody, dose-response relationship. Patients with pulmonary conditions receiving corticosteroids can generate an adequate antibody response to killed influenza virus vaccine. Long-term therapy with corticosteroids should not preclude influenza vaccination in patients with chronic pulmonary diseases who are deemed vaccine candidates.

Induction of CD8 + cytotoxic T cells by immunization with killed influenza virus and effect of cholera toxin B subunit

The MHC class I cytotoxic T-lymphocyte (CTL) response in mice given formalin-inactivated influenza whole-virus vaccine (WVV) with or without cholera toxin B subunit (CTB) was studied. Intraperitoneal injection of Balb/c (H-2 d) mice with high doses of A/Taiwan/1/86 (H1N1) WVV stimulated influenza A virus-specific CTL response in a dose-dependent manner. A dose of 4.4 or 44 μg induced CTL response equal to or greater than live influenza virus infection. Coadministration of vaccine with 5 or 25 μg of CTB resulted in a higher level of CTL than with vaccine alone. CTL lysed A/Taiwan and A/Shanghai (H3N2) virus-infectected class I-expressing P815 (H-2 d) but not virus-infected EL-4 (H-2 b) target cells nor B/Yamagata virus-infected target cells. virus-infected MHC class II- and class I-expressing A20 (H-2 d) targets were also lysed. Depletion of Lyt-2 + (CD8 +) T cells with monoclonal antibody completely abrogated lysis of P815 target cells and resulted only in a slight reduction of lysis of A20 target cells. Depletion of L3T4 + (CD4 +) T cells or NK cells had minimal effect on lysis of either P815 or A20 target cells. Using limiting dilution analysis, the precursor CTL (pCTL) frequency paralleled CTL activity. Significant CTL activity was detected 7 months after immunization. These results demonstrate that adequate doses of influenza WVV with or without CTB can induce long-lasting influenza A cross-reactive MHC class I-restricted CD8 + CTL response in mice. Thus, coadministration of influenza WVV with CTB may lead to an effective vaccine that stimulates both CTL and antibody responses.

Serial Magnetic Resonance Imaging Studies with Paramagnetic Contrast Medium: Assessment of Disease Activity in Patients with Multiple Sclerosis before and after Influenza Vaccination

Eleven patients with a relapsing-remitting form of multiple sclerosis (MS) were examined clinically and with magnetic resonance imaging scans 3 weeks before, at the day of vaccination with killed influenza virus and 3 weeks afterwards. No exacerbations were noted in the pre- or postvaccination period. Eight contrast-enhanced or active lesions were present at the onset of the study. Three new active lesions appeared at the end of the prevaccination period while only 1 new active lesion was found at the end of the postvaccination period. We conclude that vaccination with killed influenza virus has no clinical or subclinical short-term effect on the activity of MS.

Dominant lethality in mice--a test for mutagenicity of influenza X-31 virus.

The induction of dominant lethal mutation in germ cells is the cause of embryonic death resulting in the reduction of litter size in the F1 progeny. Dominant lethal mutations were induced when male mice were infected with live A2 influenza virus. The chromosomal aberrations induced in the germ cells were shown to be responsible for the dominant lethality. Killed influenza virus was also potent in inducing chromosomal aberrations in spermatocytes of mice. In light of these observations, the UV-inactivated virus was tested for its potency in induction of dominant lethality in both female and male germ cells. The virus-inoculated females were mated with uninjected males and vice versa. Both the inactivated and live virus were found to induce dominant lethality in both female and male mice, indicating that not only the live virus but also the inactivated virus is capable of bringing about chromosomal damage resulting in dominant lethality.

Enhanced murine respiratory tract IgA antibody response to oral influenza vaccine when combined with a lipoidal amine (avridine).

The adjuvant activity of avridine, a synthetic lipoidal amine, incorporated in liposomes, was studied in mice immunized orally with killed influenza virus vaccine (A/PR/8/34, H1N1). Coadministration of avridine-containing liposomes and viral antigen enhanced the remote-site IgA antibody response in the respiratory tract without a concomitant serum antibody response or side effects. The results support the possible use of mucosal adjuvants for oral immunization against respiratory pathogens.

Unchanged bronchial reactivity after killed influenza virus vaccine in adult asthmatics.

Polyvalent killed influenza virus vaccine or saline was administered subcutaneously to 27 asthmatics to investigate the effect of influenza vaccine on respiratory function and on airway responsiveness to inhaled histamine. The patients were adults with mild to moderate asthma. Airway resistance (Raw) and intrathoracic gas volume (ITGV) were measured immediately before and 2, 3 and 21 days after vaccine or saline injection. Raw and ITGV values were used to calculate specific airway conductance (SGaw). Bronchial reactivity was expressed as the provocative dose of histamine diphosphate producing a decrease of 40% in SGaw (PD40). Fourteen (87%) of 16 asthmatics who received killed virus vaccine displayed a significant rise in serum antibody level as measured by single radial haemolysis in gel test. No significant alterations in mean Raw, ITGV and SGaw values were observed after viral vaccination. The median PD40 values for histamine also remained unchanged. However, an increased bronchial reactivity was observed in some patients after administration of virus vaccine or saline. Subclinical natural infection or allergen exposure cannot be excluded as possible causes of the increased airway reactivity in these patients. The side-effects of vaccination were minimal and no more harmful than those produced by saline injection. We conclude that the killed influenza virus vaccine used is effective in boosting serum antibody levels and is suitable for adult asthmatics when prophylactic immunisation is indicated.

Effect of dimethylglycine on antibody response to influenza vaccination in horses

A double blind study evaluating the humoral response to influenza vaccination was studied in 20 age and sex matched mature horses. The horses had been immunized previously once or twice yearly but none had been vaccinated or was known to have been exposed to influenza within the preceding six months. Horses received either placebo or dimethylglycine (750 mg orally twice daily) from Days 1 through 45 and were vaccinated intramuscularly on Day 15 with a killed influenza virus vaccine containing both A 1 and A 2 serotypes. Serum hemagglutination titers were determined by 2 independent laboratories on identical serum samples drawn on Days 1, 15, and 45. No significant difference was found between the placebo and dimethylglycine treated group in the development of either A 1 or A 2 antibody titers following vaccination.

Lack of Clinical Exacerbations in Adults with Chronic Asthma after Immunization with Killed Influenza Virus

The effects of immunization with killed influenza virus vaccine were assessed by comparison with placebo in a double-blind study of 318 adult patients with chronic asthma. The patients were randomly allocated to active vaccine and placebo. No difference was observed in peak expiratory flow rate or in clinical symptoms of bronchial obstruction between the groups receiving active vaccine and placebo during the first week after immunization. The data were analyzed separately for age, sex, duration of the disease, hypersensitivity to aspirin (acetylsalicylic acid), atopic status, patients with a history of attacks of asthma induced by viral infections, patients with a diurnal variation of baseline peak expiratory flow of 20 percent or more, and patients receiving continuous oral steroid medication, but none of these factors seemed to predict any short-term adverse effects of vaccination. Follow-up for eight months after the vaccination revealed no differences in asthmatic symptoms between the patients treated with active vaccine and those receiving placebo. The antiviral antibody response to vaccination was normal. The possible protection provided by the vaccination against exacerbation of asthma induced by influenza could not be evaluated, since the influenza epidemic expected during the season failed to occur in Finland. It is concluded that immunization with killed influenza vaccine is safe and is not associated with any significant side effects in adult patients with chronic asthma.

Effects of killed and live attenuated influenza vaccine on symptoms and specific airway conductance in asthmatics and healthy subjects.

Killed and live influenza virus vaccines were given to asthmatics and healthy subjects to investigate symptoms and alterations in their respiratory performance after vaccination. Polyvalent killed influenza virus vaccine was given to 16 asthmatics and live attenuated influenza virus vaccine to 23 asthmatics and 21 healthy subjects. Fourteen of the 16 asthmatics vaccinated with the killed vaccine displayed a significant rise in serum antibody level as measured by a single radial haemolysis in gel (SRH test). 11 of the 23 asthmatics and 14 of the 21 healthy subjects vaccinated with the live attenuated vaccine displayed a significant rise in the SRH test. Among the subjects with no measurable initial antibodies and with a significant rise in the SRH test, one asthmatic vaccinated with the killed vaccine experienced symptoms of common cold with fever and dyspnoea 1 week after vaccination. Three asthmatics and four healthy subjects vaccinated with live attenuated vaccine experienced mild symptoms, mainly rhinorrhoea, cough and sore throat 2 to 3 days after vaccination. No alterations in specific airway conductance in asthmatics or in healthy subjects were observed. We conclude that both killed and live attenuated influenza virus vaccines are tolerated well by asthmatics and appear to be safe for asthma patients.

Effects of Influenza Vaccination on the Peripheral Airways of Healthy Human Volunteers

Forty-two volunteers (15 of them cigarette smokers) were studied to determine the effects on the airways that might result from immunization with killed influenza virus vaccine. The forced vital capacity, the forced expiratory volume in one second, the maximal expiratory flows at 50 and 75 percnet of vital capacity, and the volume isoflow were determined before and at 24, 48, and 72 hours and one and two weeks after vaccination. For both smokers and nonsmokers, there were no significant changes in the results of these tests of pulmonary function following vaccination.

Immunization with Killed Influenza Virus in Children with Chronic Asthma

The risk posed by immunization against influenza in asthmatic children is unclear, as is the risk posed by actual infection with influenza virus. The peak expiratory flow rate (PEFR) was measured twice daily in 79 asthmatic children following immunization with bivalent (A/Port Chalmers/1/73 and B/Hong Kong/5/72) vaccine containing killed influenza virus. A transient decrease in PEFR was most apparent at 48 hours (P < 0.05), coinciding with a significant increase in the need for treatments with nebulization of a bronchodilator drug (P < 0.01). When examined at 24 hours, the majority of subjects (49) had a decreased PEFR, but clinical exacerbation of severe asthma was rare. Protection afforded by immunization against infection with influenza virus was examined in 55 immunized and 38 control patients during a subsequent epidemic; hospitalization for influenza-like illness (P < 0.01) and for influenza-like illness accompanied by asthma (P < 0.05) was diminished. Hospitalization for asthma alone was not affected. Thus, immunization against influenza may be accompanied by transient reversible impairment of the flow of air in many asthmatic children, but morbidity from subsequent infection with influenza virus is significantly reduced, justifying continuation of the practice of prophylactic immunization against influenza.

Fluorescent Antibodies to Influenza Virus in Various Immunoglobulin Fractions of Serum after Natural Infection or Vaccination

Abstract Sera from confirmed cases of influenza and from recipients of attenuated or killed influenza virus vaccines were tested for IgM, IgA, and IgG antibodies by the indirect fluorescent antibody technique. Treatment with 2-mercaptoethanol and by sucrose density gradient centrifugation proved that IgM antibodies, as well as IgA and IgG, were located exclusively in the 7S fraction of globulin. The 7S IgM antibodies rose rapidly after onset of disease in all cases and persisted in decreasing titers for 3 months. The appearance of IgA antibodies was detected in 75% of the cases. These attained lower titers and were of shorter duration. IgG fluorescent antibody (FA) titers increased in all subjects and the levels observed were closely analogous to hemagglutination inhibition titers. The three classes of FA were proven to be independently located in their respective subunits of immunoglobulin and to be specific for either type A or B influenza virus. IgM antibody increases were measurable in 52% of the vaccinees receiving attenuated viruses administered intranasally but only 12% responded with IgA antibodies. Both classes of antibody were of lower titer and shorter duration than were those after clinical disease. Their development, titer, and decline were independent of the presence or absence of IgG antibodies. In fact, many subjects had IgG antibodies at the time of vaccination. IgM and IgA antibodies in low titers were detected in 57% of the post-inoculation specimens from persons receiving inactivated vaccine. All had responded with increased titers of antibody in the IgG fraction. Finally, it was shown that it is possible to detect recent influenza infection or vaccination by the demonstration of IgM or IgA antibodies in serum.