Genetic and subunit vaccines based on the stem domain of the equine influenza hemagglutinin provide homosubtypic protection against heterologous strains

H3N8 influenza virus strains have been associated with infectious disease in equine populations throughout the world. Although current vaccines for equine influenza stimulate a protective humoral immune response against the surface glycoproteins, disease in vaccinated horses has been frequently reported, probably due to poor induction of cross-reactive antibodies against non-matching strains. This work describes the performance of a recombinant protein vaccine expressed in prokaryotic cells (ΔHAp) and of a genetic vaccine (ΔHAe), both based on the conserved stem region of influenza hemagglutinin (HA) derived from A/equine/Argentina/1/93 (H3N8) virus.Sera from mice inoculated with these immunogens in different combinations and regimes presented reactivity in vitro against highly divergent influenza virus strains belonging to phylogenetic groups 1 and 2 (H1 and H3 subtypes, respectively), and conferred robust protection against a lethal challenge with both the homologous equine strain (100%) and the homosubtypic human strain A/Victoria/3/75 (H3N2) (70–100%). Animals vaccinated with the same antigens but challenged with the human strain A/PR/8/34 (H1N1), belonging to the phylogenetic group 1, were not protected (0–33%). Combination of protein and DNA immunogens showed higher reactivity to non-homologous strains than protein alone, although all vaccines were permissive for lung infection.     

Homologous and heterologous antibody responses to subunit influenza virus vaccine

In a group of 32 adult volunteers given subunit influenza virus vaccine containing 250 international units (i.u.) of A/Victoria/3/75, 250 i.u. of A/Scotland/840/74 and 300 i.u. of B/Hong Kong/8/73, there were substantial increases in the geometric mean homologous haemagglutination-inhibiting (HI) antibody titres. There was also substantial boosting of the antibodies to the earlier variants of the Hong Kong (H3N2) series and to a later variant of the Asian (H2N2) series. There was no boosting of antibodies to the A/FM/1/47 strain, a representative member of the H1N1 series, but two individuals showed substantial rises to A/PR/8/34 (HON1). There were increases in the HI titre of antibodies cross reactive with two recent isolations, A/Texas/1/77, and A/Victoria/35/77, but the majority of vaccinees failed to reach antibody titres likely to be protective against such strains.     

Homologous and heterologous antibody responses to subunit influenza virus vaccine.

In a group of 32 adult volunteers given subunit influenza virus vaccine containing 250 international units (i.u.) of A/Victoria/3/75, 250 i.u. of A/Scotland/840/74 and 300 i.u. of B/Hong Kong/8/73, there were substantial increases in the geometric mean homologous haemagglutination-inhibiting (HI) antibody titres. There was also substantial boosting of the antibodies to the earlier variants of the Hong Kong (H3N2) series and to a later variant of the Asian (H2N2) series. There was no boosting of antibodies to the A/FM/1/47 strain, a representative member of the H1N1 series, but two individuals showed substantial rises to A/PR/8/34 (HON1). There were increases in the HI titre of antibodies cross reactive with two recent isolations, A/Texas/1/77, and A/Victoria/35/77, but the majority of vaccinees failed to reach antibody titres likely to be protective against such strains.     

Surveillance of influenza in Houston, Texas, USA: gradual transition from A/Victoria/75 (H3N2) to A/Texas/77 (H3N2) predominance and antigenic characterization of "intermediate" strains

Influenza epidemics in Houston, Texas, USA, during the winters of 1975-76, 1976-77, and 1977-78 were attributed to A/Victoria/3/75 (H3N2), B/Hong Kong/5/72, and A/Texas/1/77 (H3N2)-like viruses, respectively. Both A/Victoria and A/Texas viruses were detected towards the end of the 1976-77 epidemic and throughout the 1977-78 epidemic. To determine if there had been a gradual transition in the predominant strain, 267 viral isolates from the 1975-76 epidemic were tested for A/Texas virus. Eight specimens (3%) that appeared to contain A/Texas antigens were cloned and retested with specific antisera prepared in guinea-pigs and ferrets. One virus was identical to A/Texas/1/77 virus, two reacted like A/Victoria/3/75 and five reacted equally well with antisera prepared against A/Victoria/3/75 and A/Texas/1/77 viruses (bridging strains). The six viral isolates containing A/Texas antigens were obtained at different times during the epidemic, from all parts of the city, from males and females aged between 1 and 20 years.     

Morphology and antigenicity studies on reassortant influenza (H3N2) viruses for use in inactivated vaccines.

Three influenza A (H3N2) reassortant whole virus vaccine strains with differing antibody-inducing capacities in hamsters were investigated morphologically and antigenically. Although initial measurements of virion circumference, from electron micrographs of vaccine preparations, suggested a relationship of small virion size with low immunogenicity, subsequent immunization with, and morphological investigation of, vaccine virions separated on sucrose gradients, failed to obtain populations whose antibody-inducing capacity clearly correlated with constituent virion density, size, morphology or integrity. However, antigenic investigation using single radial haemolysis (SRH) and monoclonal antibodies revealed significant differences in antigenic specificity between the strains. Furthermore, a series of H3N2 isolates, derived using standard reassortment procedures, also showed differences in antigenic specificity in their haemagglutination-inhibition (HI) reactions with monoclonal antibodies after five passages in allantois-on-shell cultures. Variation between these isolates and their A/Victoria parent virus could be detected using SRH and hamster sera raised against each isolate. These results demonstrate variation between candidate influenza A virus vaccine strains, all possessing the same surface (H3N2) glycoproteins, expressed as a consequence of the reassortant system used for their production.     

Morphology and antigenicity studies on reassortant influenza (H3N2) viruses for use in inactivated vaccines

Three influenza A (H3N2) reassortant whole virus vaccine strains with differing antibody-inducing capacities in hamsters were investigated morphologically and antigenically. Although initial measurements of virion circumference, from electron micrographs of vaccine preparations, suggested a relationship of small virion size with low immunogenicity, subsequent immunization with, and morphological investigation of, vaccine virions separated on sucrose gradients, failed to obtain populations whose antibody-inducing capacity clearly correlated with constituent virion density, size, morphology or integrity. However, antigenic investigation using single radial haemolysis (SRH) and monoclonal antibodies revealed significant differences in antigenic specificity between the strains. Furthermore, a series of H3N2 isolates, derived using standard reassortment procedures, also showed differences in antigenic specificity in their haemagglutination-inhibition (HI) reactions with monoclonal antibodies after five passages in allantois-on-shell cultures. Variation between these isolates and their A/Victoria parent virus could be detected using SRH and hamster sera raised against each isolate. These results demonstrate variation between candidate influenza A virus vaccine strains, all possessing the same surface (H3N2) glycoproteins, expressed as a consequence of the reassortant system used for their production.     

Generation of an attenuated H5N1 avian influenza virus vaccine with all eight genes from avian viruses

In the face of disease outbreaks in poultry and the potential pandemic threat to humans caused by the highly pathogenic avian influenza viruses (HPAIVs) of H5N1 subtype, improvement in biosecurity and the use of inactivated vaccines are two main options for the control of this disease. Vaccine candidates of influenza A viruses of H5N1 subtype have been generated in several laboratories by plasmid-based reverse genetics with hemagglutinin (HA) and neuraminidase (NA) genes from the epidemic strains of avian viruses in a background of internal genes from the vaccine donor strain of human strains, A/Puerto Rico/8/34 (PR8). These reassortant viruses containing genes from both avian and human viruses might impose biosafety concerns, also may be do if C4/F AIV would be a live attenuated vaccine or cold-adaptive strain vaccine. In order to generate better and safer vaccine candidate viruses, we genetically constructed attenuated reassortant H5N1 influenza A virus, designated as C4/F AIV, by plasmid-based reverse genetics with all eight genes from the avian strains. The C4/F AIV virus contained HA and NA genes from an epidemic strain A/Chicken/Huadong/04 (H5N1) (C4/H5N1) in a background of internal genes derived from a low pathogenic strain of A/Chicken/F/98(H9N2). The reassortant virus was attenuated by removal of the multibasic amino acid motif in the HA gene by mutation and deletion (from PQRERRRKKR (downward arrow) G to PQIETR (downward arrow) G). The intravenous pathogenicity index (IVPI) of C4/F AIV virus was 0, whereas that of the donor virus C4/H5N1 was 3.0. The virus HA titer of C4/H5N1 in the allantoic fluid from infected embryonated eggs was as high as 1:2048. The inactivated vaccine prepared from the reassortant virus C4/F AIV-induced high HI titer in vaccinated chickens and gave 100% protection when challenged with highly pathogenic avian influenza virus of H5N1 subtype.     

Efficacy of vaccination of pigs with different H1N1 swine influenza viruses using a recent challenge strain and different parameters of protection

This study investigates whether antigenic evolution within H1N1 swine influenza viruses can compromise vaccine efficacy and, specifically, whether the A/New Jersey/8/76 strain in the commercial swine influenza vaccines needs to be updated. Pigs were vaccinated twice intramuscularly with experimental monovalent vaccines derived from different H1N1 strains (A/New Jersey/8/76, Sw/Belgium/1/83 or Sw/Belgium/1/98) or with a commercial bivalent vaccine based on A/New Jersey/8/76 (H1N1) and A/Port Chalmers/1/73 (H3N2). Experimental and commercial vaccines contained a different adjuvant. Two weeks after the second vaccination, all pigs were challenged intratracheally with Sw/Belgium/1/98. Mean pre-challenge haemagglutination inhibition (HI) antibody titres against the challenge virus were lower for the experimental A/New Jersey/8/76 vaccine than for the other vaccines. The reduction in mean virus titres in the lungs was highly significant for the latter vaccines, including the commercial New Jersey-derived vaccine, but not for the experimental A/New Jersey/8/76 vaccine. Clinical signs after challenge were negligible in all vaccinates. Post-challenge levels of interferon-alpha and tumor necrosis factor-alpha in bronchoalveolar lavage fluids were reduced in the vaccinates, while levels of interleukin-1 and neutrophils were less consistent. Though the A/New Jersey/8/76 strain is less effective in preventing infection by Sw/Belgium/1/98 than the homologous virus or than Sw/Belgium/1/83, all strains can protect completely if antibody titres against the challenge virus are sufficiently high. Apart from the vaccine strain, adjuvant and antigenic dose may play a crucial role in vaccine efficacy.     

Laboratory-based surveillance of influenza virus in the United States during the winter of 1977--1978. II. Isolation of a mixture of A/Victoria- and A/USSR-like viruses from a single person during an epidemic in Wyoming, USA, January 1978

At a time when outbreaks and sporadic cases of influenza caused a A/Victoria/3/75-like and A/Texas/1/77-like H3N2 strain of influenza were occurring in the Rocky Mountain region of the USA, about 60% of the students of a high school in Cheyenne, Wyoming, were involved in an outbreak of influenza-like illness. Six influenza A(H1N1) virus isolates were obtained from throat swabs collected from 12 of these students. Virus isolated from a seventh student, however, contained a mixture of H1 and H3 (A/Victoria/3/75-like) hemagglutinins and N1 and N2 neuraminidases, as shown by the ability to clone from the mixture viruses with antigenic components H1N1, H3N1, and H3N2. An antigenic hybrid virus with H3N1 composition was re-isolated from the original throat swab. The results show that one student was shedding a mixture of A/Victoria/3/75(H3N2)-like and A/USSR/90/77(H1N1)-like viruses at the time his throat swab was taken.     

Influenza vaccination with live-attenuated and inactivated virus-vaccines during an outbreak of disease.

Immunization procedures with live attenuated and inactivated vaccines were carried out on a group of young recruits at the beginning of an outbreak of infection due to an A/Victoria/3/75-related virus strain, which occurred in February 1977 in a military camp. A retrospective investigation on protection from clinical influenza was then performed in order to investigate whether immunization with live virus vaccines, administered at the beginning of an epidemic, could provide early protection from the disease. In the course of the two weeks following vaccination, laboratory-confirmed clinical influenza cases occurred in 4 subjects among the 110 volunteers of the control group which received placebo, and in 8, 7 and 4 subjects respectively of the 3 groups of about 125 individuals, each of which received one of the following vaccine preparations: (a), live attenuated A/Victoria/3/75 influenza virus oral vaccine, grown on chick embryo kidney culture; (b), live attenuated nasal vaccine, a recombinant of A/Puerto Rico/8/34 with A/Victoria/3/75 virus; and (c), inactivated A/Victoria/3/75 virus intramuscular vaccine. These data do not support the hypothesis that, during an epidemic of infection, early protection from clinical influenza can be achieved through immunization with live attenuated or inactivated influenza virus vaccines, in spite of the high immunizing capability of the vaccine preparations.     

Efficacy of novel recombinant fowlpox vaccine against recent Mexican H7N3 highly pathogenic avian influenza virus

Since 2012, H7N3 highly pathogenic avian influenza (HPAI) has produced negative economic and animal welfare impacts on poultry in central Mexico. In the present study, chickens were vaccinated with two different recombinant fowlpox virus vaccines (rFPV-H7/3002 with 2015 H7 hemagglutinin [HA] gene insert, and rFPV-H7/2155 with 2002 H7 HA gene insert), and were then challenged three weeks later with H7N3 HPAI virus (A/chicken/Jalisco/CPA-37905/2015). The rFPV-H7/3002 vaccine conferred 100% protection against mortality and morbidity, and significantly reduced virus shed titers from the respiratory and gastrointestinal tracts. In contrast, 100% of sham and rFPV-H7/2155 vaccinated birds shed virus at higher titers and died within 4?days. Pre- (15/20) and post- (20/20) challenge serum of birds vaccinated with rFPV-H7/3002 had antibodies detectable by hemagglutination inhibition (HI) assay using challenge virus antigen. However, only a few birds (3/20) in the rFPV-H7/2155 vaccinated group had antibodies that reacted against the challenge strain but all birds had antibodies that reacted against the homologous vaccine antigen (A/turkey/Virginia/SEP-66/2002) (20/20). One possible explanation for differences in vaccines efficacy is the antigenic drift between circulating viruses and vaccines. Molecular analysis demonstrated that the Mexican H7N3 strains have continued to rapidly evolve since 2012. In addition, we identified in silico three potential new N-glycosylation sites on the globular head of the H7 HA of A/chicken/Jalisco/CPA-37905/2015 challenge virus, which were absent in 2012 H7N3 outbreak virus. Our results suggested that mutations in the HA antigenic sites including increased glycosylation sites, accumulated in the new circulating Mexican H7 HPAIV strains, altered the recognition of neutralizing antibodies from the older vaccine strain rFPV-H7/2155. Therefore, the protective efficacy of novel rFPV-H7/3002 against recent outbreak Mexican H7N3 HPAIV confirms the importance of frequent updating of vaccines seed strains for long-term effective control of H7 HPAI virus.     

Immunogenicity and protective efficacy of cold-adapted X-31 live attenuated pre-pandemic H5N1 influenza vaccines

Despite global efforts to control influenza viruses, they have taken a heavy toll on human public health worldwide. Among particular threats is highly pathogenic avian H5N1 influenza virus (HPAI) due to not only its high mortality in humans but also possible human-to-human transmission either through reassortment with other human influenza viruses such as 2009 pandemic H1N1 influenza virus, or by genetic mutations. With the aim of developing effective vaccines against the H5N1 viruses, we generated two live attenuated H5N1 vaccine candidates against A/Indonesia/05/2005 (clade 2.1) and A/chicken/Korea/ES/2003 (clade 2.5) strains, in the genetic background of the cold-adapted donor strain of X-31. In mice, a single dose of immunization with each of the two vaccines was highly immunogenic inducing high titers of serum viral-neutralizing and hemagglutinin-inhibiting antibodies against the homologous H5N1 strain. Furthermore, significant levels of cross-clade antibody responses were induced by the vaccines, suggesting a broad-spectrum cross-reactivity against the heterologous H5N1 strains. The immunizations provided solid protections against heterologous lethal challenges with H5N2 virus, significantly reducing the morbidity and challenge virus replications in the respiratory tracts. The robustness of the antibody responses against both the homologous and heterologous strains, together with efficient protection against the lethal H5N2 challenge, strongly support the protection against wild type H5N1 infections. These results could serve as an experimental basis for the development of safe and effective H5N1 pre-pandemic vaccines while further addressing the biosecurity concerns associated with H5N1 HPAI.     

Cross-reactive antibodies in middle-aged and elderly volunteers after MF59-adjuvanted subunit trivalent influenza vaccine against B viruses of the B/Victoria or B/Yamagata lineages

This study evaluated whether MF59-adjuvanted subunit trivalent influenza vaccine for the 2003/04 winter season (A/Moscow/10/99, H3N2; A/New Caledonia/20/99, H1N1; B/Hong Kong/330/01) would confer protection against mismatched and frequently co-circulating variants of influenza B/Victoria- and B/Yamagata-like virus strains. Haemagglutination inhibiting (HI) antibodies were measured in middle-aged and elderly volunteers against the homologous B/Victoria-like vaccine strain (B/Hong Kong/330/01) and against mismatched B/Victoria-like (B/Malaysia/2506/04) and B/Yamagata-like (B/Singapore/379/99 and B/Shanghai/361/02) strains. Immunization induced significant increases in the amounts of HI antibodies against all influenza B strains under investigation. However, the responses against the heterologous B/Shanghai/361/02 virus did not reach the desirable values of seroprotection. An age-dependent decline of the responses was found for B/Victoria-like antigens, but not for B/Yamagata-like strains. Although further studies are needed, our data support the recommendation of including influenza B viruses of the B/Victoria and B/Yamagata lineages in the future influenza vaccine preparations.     

中国2002～2003年度流行性感冒监测分析

目的 阐明2002年4月至2003年6月国内流行性感冒(流感)流行特点和流感病毒优势株的特性。方法 流感病毒分离采用鸡胚和细胞分离；流感病毒亚型鉴定采用血球凝集抑制试验；对流行株的HA基因核酸测序，分析其亲缘关系和抗原变异性。结果 2002年4月至2003年6月，全国23个省(市)和自治区共采集流感样患者咽拭子标本共计16135份，经鉴定流感病毒阳性1113株，分离率6．9％。在1113株流感病毒中，A1型66株、A3型544株、B型流感病毒Yamagada98株和Victoria405株，分别占总分离数的5．9％、48．9％、8．8％和36．4％。优势流行株为H3N2和B型Victoria株。A3型流感病毒除主要分离于2002年12月和2003年1月外，在非流行高峰期也有一定数量的分离。而B型Victoria系流感病毒主要集中分离于冬季流行高峰期，其流行株核酸序列分析属B型Victoria系株。A3型毒株血凝素基因的HA1系统树分析表明，其与A／Panama／2007／99同源，且有某些变异存在。结论 虽然感染人群的流感毒株依然是A1、A3和B型交叉出现，但以A型(H3N2)和B型Victoria为优势株。与历年不同，B型Victoria分离比例增加及分布广泛是2002～2003年度的特点。A型(H3N2)流行株有变异迹象值得密切注意。     

An MF59-adjuvanted inactivated influenza vaccine containing A/Panama/1999 (H3N2) induced broader serological protection against heterovariant influenza virus strain A/Fujian/2002 than a subunit and a split influenza vaccine

To test whether inactivated influenza vaccines distributed during the 2003-2004 influenza season in the northern hemisphere were able to confer protection against the mismatched variant A/Fujian/411/2002 virus strain, we measured haemagglutination inhibiting (HI) antibodies in elderly subjects vaccinated with three inactivated vaccines against the homologous A/H3N2 vaccine strain (A/Panama) and against the mismatched A/Fujian strain. The results showed that, while 76 to 80% of elder people vaccinated with conventional vaccines had protected levels of antibodies against the A/Fujian heterovariant strain, those vaccinated with the MF59-adjuvanted vaccine have protective levels of antibodies in >98% of the cases. We conclude that MF59-adjuvanted vaccines confer protection also against influenza virus strains which are not fully matched with those included in the vaccine.     

Development of broadly reactive H5N1 vaccine against different Egyptian H5N1 viruses

The H5N1 highly pathogenic avian influenza (HPAI) virus was isolated for the first time in Egypt in 2006, since then, the virus has become endemic causing a significant threat to the poultry industry and humans. H5N1 HPAI outbreaks continue to occur despite extensive vaccination programs that have been implemented nationwide in different poultry species. Several studies showed that the co-circulating H5N1 viruses in Egypt are genetically and antigenically distant raising a question on the cross protective efficacy of commercial vaccines. In this study, we introduced mutations at the antigenic sites of the hemagglutinin (HA) to broaden reactivity of the Egyptian H5N1 virus. A reverse genetically created variant H5N1 virus (A/chicken/Egypt/1063/2010) with five amino acid mutations (G140R, Y144F, I190L, K192Q, D43N) in the HA gene showed enhanced cross reactivity. This virus showed up to 16 fold increase in reactivity to the classic-lineageH5N1viruses measured by hemagglutination inhibition (HI) assay while maintaining similar level of reactivity with the variant-lineage viruses compared to wild-type virus. In addition, a single amino acid substitution (N165H), which removes potential glycosylation site at the HA globular head of two classic strains (A/chicken/Egypt/527/2012 and A/chicken/Egypt/102d/2010) broadened the reactivity to antisera generated against H5N1 viruses from different clusters. The broadened reactivity of the mutant viruses were also confirmed by testing reactivity of antisera prepared from the mutant viruses against reference viruses from both classic and variant clades. The virus neutralization test using selected antisera and viruses further confirmed the cross HI results. This study highlights that targeted mutation in the HA may be effectively used as a tool to develop broadly reactive influenza vaccines to cope with the continuous antigenic evolution of viruses.     

2006年湖南省流行性感冒病原学监测结果与分析

目的了解湖南省流感监测地区的流感流行状况及流感毒株的型别分布,分析其流行趋势,为流感防制提供科学依据。方法采集流感样病例(ILI)的咽拭子标本,用传代狗肾细胞(MDCK)进行病毒分离,采用血凝抑制实验(HI)进行流感病毒型别鉴定。分离的毒株再送国家流感中心(NIC)进行复核鉴定。结果全省12家哨点医院3499份ILI咽拭子标本,分离到毒株258株,分离阳性率为7.37%,经NIC最后复核鉴定的结果为:A(H1N1)亚型202株,A(H3N2)亚型11株,B型43株,另有2株送NIC后转阴;流感及ILI暴发疫情病例咽拭子标本179份,分离到流感病毒75株,分离阳性率为41.90%,分型鉴定为A(H1N1)亚型12株,B型62株,1株送国家流感中心后转阴。结论2006年湖南省流感监测地区全年均有流感活动,A(H1N1)亚型、A(H3N2)亚型和B型均能被分离到,A(H1N1)亚型为优势株,而暴发疫情则以B型为主。     

Serological evaluation of an influenza A virus cold-adapted reassortant live vaccine, CR-37 (H1N1), in Japanese adult volunteers

A cold-adapted influenza A virus, CR-37 (H1N1), derived from genetic reassortment between A/Ann Arbor/6/60 (H2N2) cold-adapted variant virus and A/California/10/78 (H1N1) wild-type virus, was tested in Japanese adult volunteer. The CR-37 live virus preparation induced only low-grade clinical reactions in volunteers for the first 3-4 days after inoculation. Two vaccinees who did not show any antibody changes became febrile (over 38.0 degrees C). Skin tests using the vaccine preparation and uninfected allantoic fluid were performed, and indicated that one of these two vaccines was positive for the CR-37 vaccine preparation. A high proportion of the vaccinees whose sera had a haemagglutination-inhibition (HI) antibody titre against the vaccine strain of less than or equal to 64 before inoculation, seroconverted in both HI and neuraminidase-inhibition (NAI) antibody titrations, and only a few seroconverted in the titration of antibody against type-specific internal antigens. The serological examinations against heterotypic H1N1 variants indicated that the cold-adapted live influenza virus vaccine could induce a broad spectrum of HI antibody reactivity and immunity of long duration.     

Serological evaluation of an influenza A virus cold-adapted reassortant live vaccine, CR-37 (H1N1), in Japanese adult volunteers.

A cold-adapted influenza A virus, CR-37 (H1N1), derived from genetic reassortment between A/Ann Arbor/6/60 (H2N2) cold-adapted variant virus and A/California/10/78 (H1N1) wild-type virus, was tested in Japanese adult volunteer. The CR-37 live virus preparation induced only low-grade clinical reactions in volunteers for the first 3-4 days after inoculation. Two vaccinees who did not show any antibody changes became febrile (over 38.0 degrees C). Skin tests using the vaccine preparation and uninfected allantoic fluid were performed, and indicated that one of these two vaccines was positive for the CR-37 vaccine preparation. A high proportion of the vaccinees whose sera had a haemagglutination-inhibition (HI) antibody titre against the vaccine strain of less than or equal to 64 before inoculation, seroconverted in both HI and neuraminidase-inhibition (NAI) antibody titrations, and only a few seroconverted in the titration of antibody against type-specific internal antigens. The serological examinations against heterotypic H1N1 variants indicated that the cold-adapted live influenza virus vaccine could induce a broad spectrum of HI antibody reactivity and immunity of long duration.     

Co-circulation of two influenza A (H3N2) antigenic variants detected by virus surveillance in individual communities.

From March through June 1977 a total of 31 influenza A (H3N2) viruses were isolated from students with respiratory disease who were seen at the student health service on the Berkeley campus of the University of California, and 32 influenza A (H3N2) viruses were isolated from persons who participated in a city-wide febrile respiratory disease surveillance program in Seattle. The antigenic specificity of the hemagglutinin was determined for each isolate by hemagglutination inhibition testing with sera from ferrets infected with prototype strains A/Victoria/3/75 and A/Texas/1/77. In each of the three months, April, May and June, A/Victoria/3/75-like and A/Texas/1/77-like viruses were identified among isolates from both communities, and the numbers of isolates of the two antigenic variants from patients seen with influenza-like illnesses were similar. The findings emphasize the need to examine multiple isolates even from within single communities to determine the antigenic specificity of current strains of influenza virus.