Increased sensitivity and reduced specificity of hemagglutination inhibition tests with ether-treated influenza B/Singapore/222/79

Hemagglutination inhibition (HI) tests against whole virus (WV) influenza B/Singapore/222/79 antigen detected prevaccination serum antibody in only 15 (20%) of 50 predominantly elderly volunteers and fourfold or greater titer rises in only three (6%) after they received 1981-1982 trivalent influenza vaccine containing antigens of this virus. HI titers against ether-treated (ET) B/Singapore/222/79 were about eightfold higher than those against WV antigen and were comparable to microneutralization titers against this virus. The ET HI detected prevaccination antibody in 84%, a postvaccination titer rise in 32%, and a final titer of 80 or higher in 66%. Among 51 additional persons with known or presumed influenza B virus infections early in 1982, ET B/Singapore/222/79 was also more sensitive than WV for serodiagnosis (69 versus 49%), but eight persons with both WV and ET B/Singapore/222/79 HI responses also had an HI titer rise to WV A/Brazil/11/78 (H1N1) antigen. Conversely, among 14 college students with febrile, culture-proven influenza A (H1N1) infections early in 1982, 6 (43%) developed HI titer rises to ET B/Singapore/222/79 with no other serological evidence of influenza B virus infection. Moreover, young adult volunteers with mild experimental influenza A (H1N1) infections also exhibited a 17% (3 of 18) incidence of ET B/Singapore/222/79 HI titer rises, versus none in matched, uninfected volunteers. These data indicate that ET B/Singapore/222/79 virus has increased sensitivity but reduced specificity compared to WV as an HI antigen and that caution is needed in interpretation of a single HI test for serodiagnosis, whether with WV or ET antigen.     

Evaluation of the Single Radial Hemolysis Test for Measuring Hemagglutinin- and Neuraminidase-Specific Antibodies to H3N2 Influenza Strains and Antibodies to Influenza B

Antibodies to the H3 hemagglutinin of influenza A virus could be specifically measured by single radial hemolysis (SRH) when test antigens were recombinant viruses containing the relevant H3 hemagglutinin antigen and irrelevant Neq1 neuraminidase of A/equine/Prague/1/56 virus. Antibodies to influenza B virus could also be measured by the SRH technique. Antibody rises to influenza A or B virus measured by SRH agreed with results of hemagglutination inhibition (HI) tests for about 80% of the sera tested, including sera from volunteers receiving killed influenza vaccine and sera from patients naturally infected with influenza. Correlation between antibody titers measured by SRH and HI was also good. Antibodies to the N2 neuraminidase of influenza A virus could be specifically measured by SRH when test antigens were recombinant viruses containing the relevant N2 neuraminidase antigen and irrelevant Heq1 hemagglutinin of A/equine/Prague/1/56 virus. The SRH test for neuraminidase antibodies was more strain specific than was the SRH test for hemagglutinin antibodies. Probably for this reason, agreement between neuraminidase antibody determinations in human sera by the SRH test and by the neuraminidase inhibition test was poorer than agreement between the SRH test for hemagglutinin antibodies and the HI test.     

Clinical reactivity and immunogenicity of hemagglutinin influenza vaccine

Summary Subjects aged 3–6, 16–17 and 27–50 years were vaccinated with one dose of hemagglutinin influenza virus vaccine. Clinical reactions, hemagglutination-inhibiting (HI) and strain- and type-specific complement-fixing (CF-V and CF-S) antibodies were determined in sera taken before and four weeks after vaccine administration. The results indicated that the reactogenicity of the vaccine was very low. The HI antibody response differed with the age of the vaccinees, apparently being conditioned by prior exposure to the various influenza virus subtypes. The results of CF tests using strain-specific V antigens corresponded in general with HI tests, with two marked exceptions. In the youngest group nearly half of the subjects developed CF antibody to V-Swine, while all of them remained without antibody detectable in the HI test. However, when V antigen was used instead of intact virus as hemagglutinin, the post-vaccination sera of these subjects also reacted positively in the HI test. Secondly, a number of prevaccination sera from persons aged 27–50 years possessed CF antibody to A/PR 8 in the absence of homologous HI antibody. Among these subjects the antibody response to both A/PR 8 and Swine was more marked in the CF test than in the HI test. After vaccine administration most of the subjects developed antibody or responded by an antibody increase to the S antigens of both influenza A and B. No significant differences were found after intradermal (0.1 ml) and subcutaneous (0.5 ml) administration of one dose of vaccine.     

Antibody reactive in antibody-dependent cell-mediated cytotoxicity following influenza virus vaccination

The antibody reactive in antibody-dependent, cell-mediated cytotoxicity (ADCC) to influenza virus-infected cells was measured in two groups of seven volunteers each, before and after immunization with inactivated or live attenuated A/Victoria/3/75 influenza virus vaccines. Age-matched controls were seven adult individuals who experienced natural influenza infection due to A/Victoria/3/75-like virus strain. After inactivated whole influenza virus immunization all the subjects showed a significant rise of the antibody reactive in ADCC (from a mean value of 4.7% to 17.1% cytotoxicity, before and 5 weeks after immunization, respectively) as well as of hemagglutination inhibition (HI) antibody (fourfold or greater increase). These immune responses were similar to those observed among naturally infected controls. After live attenuated virus vaccination, no significant increase in titer of antibody reactive in ADCC was detected, even though the vaccine induced significant increase of HI antibody titer. Little correlation was found between ADCC and HI antibody rises in sera of recipients of inactivated virus vaccine and of naturally infected individuals, while, in live attenuated influenza virus vaccinees, the rise of HI antibody titer did not correspond to a significant increase of ADCC antibody titer; several subjects who developed a significant rise in ADCC antibody titer did not show significant variation in antibody to neuraminidase and/or to complement fixation influenza virus antigens.     

Attenuated influenza A vaccine (Alice) in an adult population: vaccine-related illness, serum and nasal antibody production, and intrafamily transmission.

Ninety-five healthy adults, ages 18 to 56 years, received two intranasal doses, 2 weeks apart, of a live, attenuated, influenza type A (H3N2) vaccine (an inhibitor-resistant recombinant strain of A/England/42/72 named "Alice"). Ninety-two persons were given placebos similarly. Ninety-three percent of 68 subjects with initial serum hemagglutination-inhibition (HI) titers of greater than or equal to 1:40 to influenza A (H3N2) had a fourfold or greater antibody increase in postvaccination sera. Forty-four percent of 27 subjects with an initial HI titer of greater than or equal to 1:80 had similar increases. Overall, 77% of vaccinees had fourfold or greater antibody titer increases. Vaccinees had geometric mean serum HI titers (GMT) of 1:26, 1:123, and 1:166 at 0, 14, and 30 days, respectively. The GMTs for placebos were 1:21, 1:22, and 1:21. Thirty-five vaccinees were examined for both serum and nasal antibody; 89% had significant increases in one or both. Nasal antibody response was directly related to the level of initial serum HI titer in that 83% of 12 persons with prevaccination HI titers of 1:80 greater than or equal to 1:80 showed significant nasal antibody rises, whereas only 61% of the remaining 23 subjects with prevaccination HI titers of less than or equal to 1:40 did so. The number and severity of clinical signs and symptoms reported by vaccinees and placebos did not differ significantly. The greatest differences noted between groups were for nasal congestion on days 0 to 6 (8.3%) and rhinitis on days 14 to 20 (5.9%). Four vaccinees shed Alice after primary vaccination, but viral titers were low (10 to 100 tissue culture-infective doses/ml). One member in each of 15 cohabiting male-female couples received Alice while the other received a placebo; one of the placebo members had significant increases in serum and nasal antibody, indicating a possible transmission.     

Increasing doses of purified influenza virus hemagglutinin and subvirion vaccines enhance antibody responses in the elderly.

The reactogenicities and immunogenicities of two influenza virus vaccines were compared in a placebo-controlled clinical trial among healthy ambulatory persons > or = 65 years old (mean age, 72 years). Volunteers were assigned randomly to receive 15-, 45-, or 135-micrograms doses of monovalent influenza A/Taiwan (H1N1) hemagglutinin (HA) or subvirion (SV) vaccine intramuscularly or a placebo. Increasing doses of SV vaccine were associated with a higher rate of injection site discomfort (P < 0.05; chi-square test for linear trend), but all doses of both vaccines were well tolerated. Increasing the dose of the HA or the SV vaccine resulted in increasingly higher postimmunization levels of serum hemagglutination inhibition and neutralizing antibody levels (P < 0.001; multiple linear regression). Mean serum antibody titers at 1 month increased two- to threefold with a ninefold increase in dose; the frequencies of fourfold or greater rises in titer likewise increased. An increase in the dose of the HA or the SV vaccine also resulted in increased frequencies of rises in immunoglobulin A or G antibody titers in nasal wash specimens. The frequencies increased approximately twofold for each vaccine with a ninefold increase in the dose. These data suggest that increasing the HA vaccine dose is a promising approach to the development of improved influenza virus vaccines for use in elderly people.     

Further evidence for common antigens in herpes simplex and varicella-zoster viruses

To elucidate the mechanism of heterologous antibody responses to herpes simplex virus (HSV) and varicella-zoster virus (VZV) which occur in some patients with HSV or VZV infections, stronger evidence was sought for the existence of cross-reacting antibodies to these viruses, using antibody absorption procedures. Absorption of sera from initial HSV infections with HSV antigen was found to abolish heterologous antibody titer rises to VZV, as demonstrated in complement fixation, neutralization, and anti-complement immunofluorescence test systems. In most instances, convalescent-phase titers to heterologous VZV were reduced by HSV absorption to levels comparable to those in the acute-phase serum, indicating that cross-reacting antibodies were, in fact, responsible for the heterologous antibody titer rises. Absorption of convalescent-phase sera from HSV or VZV patients with homologous antigen also abolished or greatly diminished immunoprecipitating activity with the heterologous antigen, furnishing additional evidence of the existence of cross-reacting antibodies. Absorption of sera with insolubilized IgG to re-remove rheumatoid factor, which was present in a number of the sera studied, had no effect on either homologous or heterologous antibody titer increases. The demonstration of cross-reacting antibodies to HSV and VZV supports the concept that these two human herpesviruses share common antigen(s).     

Hemagglutinin inhibition with ether-treated antigen as a more sensitive method to measure the immunological response to an asian influenza virus vaccine

Summary The appearance of antibodies in the sera of 31 adults receiving a monovalent formalin-inactivated Asian influenza virus vaccine, in August-September 1957, has been studied by complement fixation (CF) and hemagglutinin-inhibition (HI) tests.When crude allantoic fluid antigen of the pure egg line of A/Japan/305/57 virus was used in the HI tests, none of the 31 paired sera tested showed any significant titer rise. On the other hand, with ether treated virus of the same line as antigen, 16 paired sera out of 31 gave a significant (fourfold or higher) HI titer rise.Significant CP titer rises were observed in 5 out of 17 paired sera tested. Ether treatment of the antigen did not increase the sensitivity of the CF tests.CF titer rises against the soluble antigen extracted from the virus by ether treatment were observed in 5 paired sera out of 15 tested.Ether treatment of the virus also increased the sensitivity of HI tests performed with 4 sera from individuals recovering from natural Asian influenza infection.Treatment of the virus with ethyl ether prior to its use in the HI tests did not alter the specificity of the reaction, as shown by control HI tests with ether treated PR 8 or Swine S-15 viruses.The possible mechanisms of the increased sensitivity of HI tests with ether treated virus antigen are discussed. It is suggested that ether treatment of the virus removed an excess of soluble antigen coating the virus particles, which may have interfered in the reaction between the hemagglutinins and the hemagglutimn-inhibiting antibodies.WHO Fellow at the Harvard University School of Public Health, temporarily working in the Department of Preventive Medicine, University of Pennsylvania.     

Differences in antibody responses of individuals with natural infection and those vaccinated against pandemic H1N1 2009 influenza

The differential antibody response measured by the commonly used hemagglutination inhibition (HI) and microneutralization (MN) assays in patients with natural infection and vaccination has not been fully assessed. HI and conventional MN (CMN) assays were performed on sera from 651 patients with natural infection by pandemic H1N1 2009 influenza virus and on sera from 567 recipients of the corresponding vaccine. Surprisingly, the overall seroprotection rates determined by CMN and HI assays in vaccine recipients were only 44.8 and 35.1%, respectively. Antibody titers measured by the CMN assay was significantly higher than that obtained by HI assay in vaccine recipients aged ≥50 years, but these titers were not significantly different among younger vaccine recipients. In contrast, the HI titer was greater than the CMN titer for the age group from 16 to 29 years but was not significantly different in other age groups for natural infection. Lower antibody levels were found in both naturally infected patients and immunized recipients in the older than in the younger age groups, but naturally infected patients exhibited higher HI and CMN titers than did the corresponding vaccine recipients. In addition, we developed a rapid fluorescent focus microneutralization (FFMN) assay to test sera from naturally infected patients. The FFMN assay has a better correlation with CMN than with HI (ρ = 0.810 versus 0.684), which is expected of neutralizing antibody mainly targeted toward the inhibition of viral entry into cells. The higher antibody level elicited by natural infection than by vaccination may be related to differences between antigen presentation by the intramuscular route of vaccination and mucosal viral replication in mucosal cells of the respiratory tract.     

Appearance and Persistence of Antibodies Against Different Virus Components After Regular Measles Infections

Different measles virus-specific antibody activities in acute, early (11 to 40 days after rash) and late (4 to 20 years postinfection) convalescent sera and gamma globulin were determined. Early immunoglobulin G antibodies gave a poor neutralization, which was increased 10- to 60-fold by addition of anti-gamma globulin.There was a high degree of correlation between titers of hemolysis-inhibiting (HLI) and hemagglutinating-inhibiting (HI) antibodies. However, in one out of fifteen late convalescent sera an HLI antibody titer of 640 in the presence of titer of only 20 in HI tests with Tween 80-either-treated antigen was found. Similar findings were made with sera from two patients with multiple sclerosis included in a parallel study. A somewhat higher titer of HI antibodies was demonstrable in these three sera when untreated material was used as antigen. These findings are interpreted in the following way. Antibodies against the hemagglutinin can block not only virus-specific agglutination but also lysis of red cells. In contrast, antibodies against the hemolysin, besides blocking the biological activity of this component, carry only a slight HI activity. This HI activity can be detected only by use of antigen preparations containing hemagglutinin-associated hemolysin.Complement-fixation (CF) and immunodiffusion tests (the latter were carried out with antigen preparations treated with 0.25% sodium dodecyl sulfate) demonstrated that, in almost all cases, antibodies against nucleocapsid structures dominated quantitatively among antibodies appearing in connection with and persisting after regular measles infections. Generally, only low titers of antibodies reacting with purified small particle hemagglutinin (HA; 10 to 14S) or additional structural or nonstructural components were identified in CF and immunodiffusion tests.     

Evaluation of Influenza Virus A/H3N2 and B Vaccines on the Basis of Cross-Reactivity of Postvaccination Human Serum Antibodies against Influenza Viruses A/H3N2 and B Isolated in MDCK Cells and Embryonated Hen Eggs

The vaccine strains against influenza virus A/H3N2 for the 2010-2011 season and influenza virus B for the 2009-2010 and 2010-2011 seasons in Japan are a high-growth reassortant A/Victoria/210/2009 (X-187) strain and an egg-adapted B/Brisbane/60/2008 (Victoria lineage) strain, respectively. Hemagglutination inhibition (HI) tests with postinfection ferret antisera indicated that the antisera raised against the X-187 and egg-adapted B/Brisbane/60/2008 vaccine production strains poorly inhibited recent epidemic isolates of MDCK-grown A/H3N2 and B/Victoria lineage viruses, respectively. The low reactivity of the ferret antisera may be attributable to changes in the hemagglutinin (HA) protein of production strains during egg adaptation. To evaluate the efficacy of A/H3N2 and B vaccines, the cross-reactivities of postvaccination human serum antibodies against A/H3N2 and B/Victoria lineage epidemic isolates were assessed by a comparison of the geometric mean titers (GMTs) of HI and neutralization (NT) tests. Serum antibodies elicited by the X-187 vaccine had low cross-reactivity to both MDCK- and egg-grown A/H3N2 isolates by HI test and narrow cross-reactivity by NT test in all age groups. On the other hand, the GMTs to B viruses detected by HI test were below the marginal level, so the cross-reactivity was assessed by NT test. The serum neutralizing antibodies elicited by the B/Brisbane/60/2008 vaccine reacted well with egg-grown B viruses but exhibited remarkably low reactivity to MDCK-grown B viruses. The results of these human serological studies suggest that the influenza A/H3N2 vaccine for the 2010-2011 season and B vaccine for the 2009-2010 and 2010-2011 seasons may possess insufficient efficacy and low efficacy, respectively.     

Antigenic alteration of influenza B virus associated with loss of a glycosylation site due to host-cell adaptation

Effects of host-cell adaptation of the hemagglutinin (HA) protein were evaluated by the analyses of four pairs of recent influenza B field isolates, each pair consisting of an Madin Darby canine kidney (MDCK)- and an embryonated chicken egg-derived isolates from the same clinical specimen. Among the isolates examined, all of the MDCK-derived isolates retained glycosylation site at amino acid 197 on the HA1 molecule, whereas three egg-derived isolates lost it. Antigenic difference in the HA molecule between an MDCK- and an egg-derived isolates of three of these pairs was demonstrated to be associated with the glycosylation 197. Replication of the MDCK-derived isolates was suppressed in eggs, suggesting that the presence of the glycosylation 197 was disadvantageous to replication in eggs. Virus-binding affinity assay revealed that the loss of carbohydrate chain did not significantly alter the preferential recognition of sialic acid linkage. Immunogenicity and vaccine efficacy of an MDCK- and an egg-derived clones of B/Akita/27/2001, the former retained the glycosylation 197 and the latter lost it, were compared in a hamster model. When formalin-inactivated whole virion vaccines prepared from the paired isolates were administered into hamsters, no significant difference between them was observed in protective ability against challenges by the homologous and heterologous clones. Implication of the egg adaptation of influenza virus to antigenic surveillance of the field isolates as well as the selection of vaccine strains, and possibility of the involvement of the viral protein(s) other than the HA in the egg adaptation were discussed.     

Impaired serum antibody response to inactivated influenza A and B vaccine in renal transplant recipients.

Before and after vaccination with a commercial inactivated influenza vaccine containing A/Aichi/2/68 (H3N2) and B/Massachusetts/1/71 antigens, the serum hemagglutination inhibition antibody titers to homologous and heterologous strains of A and B influenza viruses were measured in 45 renal transplant patients and 66 healthy controls (62 for the B strains). At least a fourfold titer rise to the homologous A strain occurred in 14 of 45 transplant patients (31%) versus 37 of 66 controls (56%). Fourfold or greater heterologous A rises occurred in only 8 of 45 transplant patients (18%) compared with 40 of 60 controls (61%). In both the homologous and heterologous B responses, at least fourfold hemagglutination inhibition titer rises were seen in significantly fewer transplant patients than control subjects. In the transplant group, no correlation was observed between degree of antibody response and age, previous influenza vaccination, percentage of patients initially seronegative, time since transplantation, dose of immunosuppressive drugs, level of renal function, or nature of original renal disease.     

Use of immunoenzyme analysis employing a staphylococcal protein A conjugate with peroxidase in the serodiagnosis of influenza

A test-system was developed on the basis of solid-phase enzyme-immunoassay using protein A/peroxidase conjugate for the determination of antibody levels to influenza virus in sera of humans who had experienced a natural infection or received a live influenza vaccine. The accurate observation of the test conditions was demonstrated to give the results well correlating with those of the HI test. The use of isolated hemagglutinin as the antigen considerably increased the specificity of the enzyme-immunoassay and in a number of cases detected a 4-fold or higher rise of antibody titres to hemagglutinin in paired sera of the vaccinees where the HI test showed no rise in antibody titres.     

Neutralization enzyme immunoassay for influenza virus.

A neutralization enzyme immunoassay (N-EIA) was developed for the detection of antibody titer rises in sera of patients infected with influenza A (H3N2) virus. In this N-EIA, a selected strain of influenza A (H3N2) virus was added to monolayers of LLC-MK2 cells in microtiter plates. After 24 h, the replicated virus could be demonstrated with a virus-specific enzyme-labeled monoclonal antibody. Preincubation of the influenza virus with convalescent-phase sera of patients infected with influenza A (H3N2) virus resulted 1 day later in decreased absorbance values that could be used for calculation of neutralization titers. From use of paired serum samples from 10 patients with a history of flu-like symptoms, the results obtained with N-EIA correlated well (r = 0.83) with those of the standard hemagglutination inhibition test.     

New passive hemagglutination assay kit that uses hemagglutinin-sensitized erythrocytes for detection of rubella antibodies.

A new passive hemagglutination assay for the detection of antibodies to rubella virus hemagglutinin (PHAST-Rubella) was compared with the hemagglutination inhibition (HI) test and another passive hemagglutination test that uses a soluble rubella virus antigen (SA-PHA). When the immune responses of vaccinated individuals were monitored, similar rises in antibody titer were detected by HI or PHAST-Rubella, whereas the rise in titer detected by SA-PHA was delayed. Early-phase vaccine-induced immunoglobulin M antibody analyzed by sucrose gradient fractionation was detected to the same degree by HI and PHAST-Rubella, but early-phase immunoglobulin G antibody reacted more strongly in the HI test. When acute and convalescent serum pairs from rubella-infected individuals were evaluated, a fourfold rise in titer was detected by PHAST-Rubella and HI in 15 of 15 pairs, whereas SA-PHA, which is not intended for detecting antibody titer rises in acute infections, detected a rise in titer in only 3 of 15 pairs. In studies to determine rubella immune status, testing of 1,078 premarital and random serum specimens resulted in 98.6% agreement among the three methods in identifying rubella antibody-positive and -negative individuals. For the quantitative PHAST-Rubella procedure, a coefficient of correlation of 0.93 was obtained, in comparison with HI, when a panel of 40 characterized sera were tested. These results indicate that PHAST-Rubella reagents can detect rubella antibodies as well as HI reagents and thus may be used as a fast and accurate means of determining rubella immune status and for the quantitation of rubella antibodies.     

Local and systemic antibody responses in high-risk adults given live-attenuated and inactivated influenza A virus vaccines.

Forty seropositive older adults with chronic diseases were vaccinated intranasally with either influenza A/California/10/78 (H1N1) (CR37) or influenza A/Washington/897/80 (H3N2) (CR48) virus. No clinically significant decrements in pulmonary function occurred postvaccination. Eight (62%) recipients of CR37 virus and 16 (59%) recipients of CR48 virus became infected with vaccine virus, as indicated by a fourfold rise in nasal wash immunoglobulin G (IgG) or IgA antibody titer, a fourfold rise in serum antibody titer, isolation of vaccine virus from nasal washings, or all of these. Within 2 years after cold-recombinant virus vaccination, 29 vaccinees received trivalent inactivated influenza virus vaccine parenterally. After inactivated virus vaccination, 23 (79%) vaccinees developed a fourfold rise in nasal wash or serum antibody titer to H1 antigen and 24 (83%) developed a fourfold rise in nasal wash or serum antibody titer to H3 antigen. Significantly more cold-recombinant virus vaccinees developed a fourfold rise in nasal wash IgA antibody to H1 or H3 hemagglutinin compared with inactivated virus vaccinees (17 [43%] versus 9 [17%], P = 0.01). We conclude that these cold-recombinant virus vaccines are safe and immunogenic in seropositive older high-risk adults and more often induced a nasal wash IgA antibody response than the inactivated virus vaccine.     

Serological diagnosis of influenza B virus infection: comparison of an enzyme-linked immunosorbent assay and the hemagglutination inhibition test.

The sensitivity of an enzyme-linked immunosorbent assay (ELISA) for the detection of antibody to influenza B virus was compared with that of the hemagglutination inhibition test on acute- and convalescence-phase sera obtained from adults and children infected with influenza B virus. Two whole virus, tissue culture-grown antigen preparations were used in the ELISA, influenza B/West Virginia/81 and influenza B/Hong Kong/72. Four antigens were used in the hemagglutination inhibition test. These included the tissue culture-grown whole virus antigens that were used in the ELISA. In addition the standard egg-grown antigens, influenza B/Singapore/79 and influenza B/Hong Kong/72, were included for comparison. The ELISA antibody titer was significantly correlated to the hemagglutination inhibition antibody titer, and 10 of 10 adults and 17 of 21 children infected with influenza B had fourfold antibody increases as detected by ELISA with either antigenic type of tissue culture-grown whole virus. Increases in geometric mean antibody titers of 16- to 71-fold were detected by ELISA. Increases in geometric mean antibody titers of 3- to 10-fold were detected by hemagglutination inhibition depending on the type of antigen utilized. We found that ELISA with whole virus antigens was a sensitive and specific test for the detection of antibody to influenza B virus.     

Enzyme immunoassay, complement fixation and hemagglutination inhibition tests in the diagnosis of influenza A and B virus infections. Purified hemagglutinin in subtype-specific diagnosis

The efficacy of enzyme immunoassay (EIA) in detecting diagnostic antibody rises to influenza A and B viruses was compared with complement fixation (CF) and hemagglutination inhibition (HI) tests in 455 patients with an acute respiratory infection. EIA and HI detected significantly more diagnostic antibody rises against influenza A than the CF method (96 and 87 vs. 47, respectively). In the case of influenza B significantly more diagnostic influenza B antibody rises were observed by EIA than by CF or HI (59 vs. 37 and 40, respectively). In most of the cases antibody rises in EIA were found in both IgG and IgA isotypes whereas increases in IgM antibodies were seen less frequently. Purified hemagglutinins (HA) were prepared from influenza A HI- and H3-subtypes and from influenza B viruses and used as antigens in EIA and the results were compared with those of HI. Infections caused by influenza A HI-subtype showed good homologous antibody responses in EIA but heterologous antibody responses to H3-subtype and influenza B HAs were frequently observed. Heterologous responses were clearly less frequent in patients with infections caused by the H3-subtype. Influenza B infections occasionally raised HA antibodies against influenza A H1-subtype but not to the H3-subtype. Interestingly, HI detected these heterologous responses at least as frequently as EIA. When whole viruses were used as antigens in EIA, subtype specificity was not observed and cross-reactions between influenza A and B virus antibodies were found. These observations suggest that, although EIA can show greater diagnostic efficacy over HI and CF methods, HI is still the serological method of choice in determining the causative subtype of influenza A virus infection.     

Clinical trial with "R-75" strain live, attenuated, serum inhibitor-resistant intranasal influenza B vaccine.

The "R-75" strain live, attenuated, serum inhibitor-resistant influenza B vaccine was administered intranasally by drops in two doses 14 days apart to 21 volunteers. Each vaccinee was paired with a close associate (roommate or workmate) who similarly received two doses of a placebo solution. Although about 50% of both vaccine and placebo recipients complained of symptoms after dosage, the severity of symptoms was greater in vaccine recipients. Fourfold serum hemagglutination-inhibiting antibody titer rises occurred in 38% of vaccine recipients, and four vaccines had fourfold titer rises of nasal hemagglutination-inhibiting antibody. Vaccine virus was isolated from three asymptomatic vaccine recipients. There was no virological or serological evidence of the vaccine virus spreading to placebo recipients.