Influenza activity in Czechoslovakia and the USSR, 1980-1985

Between 1980 and 1985, Czechoslovakia had experienced 4 and the USSR 3 major influenza outbreaks. Of the 3 epidemic outbreaks in the USSR, 2 were associated with influenza B virus (in the 1980/81 and 1983/84 seasons) and 1 with influenza A virus of the H3N2 subtype. In the USSR, influenza A (H1N1) virus never predominated as a cause of epidemic during the 5 years period. In Czechoslovakia, 2 epidemics (in the 1980/81 and 1983/84 seasons) were due to influenza A (H1N1) virus. The epidemic in the 1981/82 season had two waves of unequal heights and a mixed type B and subtype A (H3N2) etiology; a two-wave epidemic associated with isolates of influenza A (H1N1) and influenza B viruses was also recorded in the 1983/84 season. The influenza A (H3N2) epidemic in 1983 was of explosive character. All influenza viruses circulating in the two countries between 1980 and 1985 were of the same antigenic profile, but were isolated from the epidemics that occurred in different influenza seasons. The virological surveillance revealed strains of virus closely related to drift variants detected from outbreaks in 1977-1979 and the new variants A/Chile 1/83, A/Philippines 2/82, A/Caen 1/84 and B/USSR 100/83.     

The herald waves of influenza virus infections detected in Sendai and Yamagata cities in 1985-1990

The community surveillance of respiratory virus infections performed during 1985-1987 in Sendai and 1988-1990 in Yamagata has identified a total of five herald waves of influenza virus infections: A/H3N2 virus infections in 1985 and 1989, A/H1N1 virus infections in 1986 and 1988, and type B virus infections in 1989. To investigate the antigenic and genetic relationships between the herald wave and epidemic strains, influenza A/H1N1 viruses isolated during the 1986 and 1988 herald waves were compared with those isolated during the 1986-1987 and 1988-1989 epidemic seasons, respectively, utilizing hemagglutination inhibition tests with anti-hemagglutinin monoclonal antibodies and oligonucleotide mapping of total viral RNAs. The results showed that multiple variants differing in antigenic and genetic properties were cocirculating during the 1986 herald wave as well as during each of the two epidemics (only one strain was isolated in the 1988 herald wave). It was also observed that viruses which had the antigenic and/or genetic characteristics closely similar to those of the viruses circulating in the 1986 and 1988 herald waves, were isolated during the winters of 1986-1987 and 1988-1989, respectively.     

Assessment of the effectiveness of inactivated influenza vaccines for adults

In 9 controlled epidemiological observations (1977-1984) the effectiveness of modern Soviet whole-virion vaccines was studied in organized groups of adults and at industrial enterprises. During the epidemic outbreaks of influenza of different etiology and intensity morbidity rate in influenza and acute respiratory diseases was shown to decrease 1.1-2.2 times among the vaccinees, depending on the correspondence of epidemic and vaccine influenza strains. The absence of influenza virus B in inactivated influenza vaccines was the reason for their low effectiveness during influenza outbreaks of mixed etiology B + A (H1N1).     

The epidemic spread of the influenza A and B viruses in the USSR in 1985-1986

The data on the spread of influenza A and B in the autumn and winter of 1985-1986 are given. Three epidemics caused by all presently circulating viruses, B, A (H3N2) and A (H1N1), were registered in the USSR. Of these, the greatest one was the epidemic of influenza B; morbidity rate among the adult population during this epidemic was at the level with the morbidity rate characteristic of the epidemics registered at the period of 1962-1972, and morbidity rate among children, especially school children, was even higher.     

Properties of current influenza A (H1N1) virus strains and the characteristics of the epidemics they induce

Three epidemics of influenza A (H1N1) occurring in 1977, 1979 and 1981 were studied. These epidemics were found to be gradually dying down, which was manifested by progressively decreasing morbidity rate, the frequency and intensity of seroconversions, as well as by a decrease in the duration of the epidemic period. Changes in the biological properties of influenza A (H1N1) virus were accompanied by changes in its antigenic properties. The drift of neuraminidase in the influenza A (H1N1) virus of 1981 towards increased relationship with neuraminidase in the virus of 1952 was observed, while hemagglutinin in the strains of each of these two groups retained its individual character.     

Influenza A/H1N1 2009 Pandemic and Respiratory Virus Infections,Beijing, 2009–2010

To determine the role of the pandemic influenza A/H1N1 2009 (A/H1N1 2009pdm) in acute respiratory tract infections (ARTIs) and its impact on the epidemic of seasonal influenza viruses and other common respiratory viruses, nasal and throat swabs taken from 7,776 patients with suspected viral ARTIs from 2006 through 2010 in Beijing, China were screened by real-time PCR for influenza virus typing and subtyping and by multiplex or single PCR tests for other common respiratory viruses. We observed a distinctive dual peak pattern of influenza epidemic during the A/H1N1 2009pdm in Beijing, China, which was formed by the A/H1N1 2009pdm, and a subsequent influenza B epidemic in year 2009/2010. Our analysis also shows a small peak formed by a seasonal H3N2 epidemic prior to the A/H1N1 2009pdm peak. Parallel detection of multiple respiratory viruses shows that the epidemic of common respiratory viruses, except human rhinovirus, was delayed during the pandemic of the A/H1N1 2009pdm. The H1N1 2009pdm mainly caused upper respiratory tract infections in the sampled patients; patients infected with H1N1 2009pdm had a higher percentage of cough than those infected with seasonal influenza or other respiratory viruses. Our findings indicate that A/H1N1 2009pdm and other respiratory viruses except human rhinovirus could interfere with each other during their transmission between human beings. Understanding the mechanisms and effects of such interference is needed for effective control of future influenza epidemics.     

The laboratory epidemiological study of the joint circulation of the influenza virus A subtypes A/H1N1/ and A/H3N2/ in Bulgaria]

The National Influenza Center of Bulgaria made the epidemiological analysis of the spread of influenza virus, type A, for the period of 11 years on the basis of mass laboratory investigations. Subtype A (H1N1) was found to be the main factor of epidemics in 1978 and 1982, while the epidemics of 1980, 1983, 1985, 1986, 1987 and 1988 were mainly caused by subtype A (H3N2). The data of laboratory and epidemiological studies indicated that after 20-year absence influenza virus A, subtype A (H1N1), was found again to circulate among the population of Bulgaria, and in 1978-1988 circulated simultaneously with the previous subtype A (H3N2). The simultaneous circulation of two subtypes of influenza virus was of great importance for the frequency, spread and duration of influenza epidemics.     

Comparison of influenza outbreaks in the Republic of Kazakhstan and Russia induced by 2009 yearly new variant of A(H1N1) influenza virus

The aim of the work is the comparison of the epidemiology of influenza and acute respiratory virus infections(ARVI)in the Republic of Kazakhstan with the corresponding influenza epidemic in Russia induced by influenza pandemic virus A/California/07/2009 in 2009. Data on influenza and ARVI from the Republic of Kazakhstan and Federal Center of influenza was collected and investigated over the course of several weeks from hospitalized patients with the same diagnosis among all population and in age groups on 16 territories of Kazakhstan and in 49 major cities of Russia. The epidemic in Kazakhstan resembled the Russian epidemic in terms of its abnormally early beginning,expression of monoaetiology,the spread of the epidemic into all territories and start of the epidemics among adult population. High percentage of hospitalized people and lethal outcome were registered in this epidemic. Similarity of epidemic process character in corresponding border-line territories of both countries was found out.     

Results of virological and serological studies of three influenza A Hong-Kong epidemics in Leningrad.

An analysis of morbidity of the population in the course of 3 influenza A/Hong-Kong epidemics showed a pronounced decrease in influenza affection of adult population in the last epidemic in 1971--1972. Comparative studies of the diagnostic value of CFR and HIT demonstrated identical sensitivity of CFR as a method of influenza diagnostics in both the epidemic and interepidemic periods. HIT was suitable for the detection of influenza only in the epidemic period. In the interepidemic period, the percentage of influenza infection diagnosed by means of HIT ammounted to only 23--24 of all serologically confirmed cases of influenza. The highest percentage of virus isolation was observed when material from patients with serologically confirmed influenza was used. All strains of influenza A virus isolated in 1969 and 1970 were similar in their sensitivity to inhibitors of animal sera. During the last influenza epidemic, 2 of the 136 isolated strains were found to be resistant to gamma inhibitors and highly sensitive to the inhibitors showed their close relationship to gamma inhibitors. Antigenic analysis of the influenza A strains isolated during the 3 influenza epidemics revealed changes in the antigenic structure of the agents of the influenza epidemic in Leningrad in comparison with the standard strain A/Hong-Kong/I/68 (H3N2).     

Age Distribution of Influenza Like Illness Cases during Post-Pandemic A(H3N2): Comparison with the Twelve Previous Seasons,in France

In France, the 2011–2012 influenza epidemic was characterized by the circulation of antigenically drifted influenza A(H3N2) viruses and by an increased disease severity and mortality among the elderly, with respect to the A(H1N1)pdm09 pandemic and post-pandemic outbreaks. Whether the epidemiology of influenza in France differed between the 2011–2012 epidemic and the previous outbreaks is unclear. Here, we analyse the age distribution of influenza like illness (ILI) cases attended in general practice during the 2011–2012 epidemic, and compare it with that of the twelve previous epidemic seasons. Influenza like illness data were obtained through a nationwide surveillance system based on sentinel general practitioners. Vaccine effectiveness was also estimated. The estimated number of ILI cases attended in general practice during the 2011–2012 was lower than that of the past twelve epidemics. The age distribution was characteristic of previous A(H3N2)-dominated outbreaks: school-age children were relatively spared compared to epidemics (co-)dominated by A(H1N1) and/or B viruses (including the 2009 pandemic and post-pandemic outbreaks), while the proportion of adults over 30 year-old was higher. The estimated vaccine effectiveness (54%, 95% CI (48, 60)) was in the lower range for A(H3N2) epidemics. In conclusion, the age distribution of ILI cases attended in general practice seems to be not different between the A(H3N2) pre-pandemic and post-pandemic epidemics. Future researches including a more important number of ILI epidemics and confirmed virological data of influenza and other respiratory pathogens are necessary to confirm these results.     

Epidemiology of the Hong Kong/68 Variant of Influenza A2 in Britain

Two influenza epidemics in Britain in 1968-9 and 1969-70, were due to the Hong Kong/68 variant of influenza A2 virus. The first epidemic was prolonged with low morbidity and mortality rates; the second was sharp with high rates. The difference between total morbidity and mortality in the two epidemics, however, was less than it appeared to be—the estimated excess morbidity and mortality due to all causes in 1969-70 was only about 50% greater than in 1968-9.Antibody studies showed that about one-quarter of two groups of adults investigated were infected in the first epidemic and about one-third in the second. After the two epidemics about one-third still had no antibody to the A2/Hong Kong/68 virus.     

Do influenza epidemics spread to neighbouring countries?

This study compares the main causes of influenza epidemics reported in Czechoslovakia (CSR) and the German Democratic Republic (GDR) during the 9 seasons between 1980 and 1988. The influenza epidemics due to identical virus types were experienced in the two countries in the 1980, 1984 and 1986 seasons, and of these only the 1984 epidemic associated with A-strain influenza A/Chile/1/83 (H1N1) virus could be demonstrated to spread from the eastern parts of the CSR to the northern areas of the GDR. This implies that influenza epidemics due to identical drift variants spread only exceptionally from one country to the other during the period of observation, in spite of a busy tourist activity across the borderline.     

Asian Influenza in 1963 in Two General Practices in Cambridge,England

A clinical, epidemiological and virological investigation was conducted on patients in two general practices in Cambridge, England, during an influenza epidemic between February and April 1963. The epidemiological pattern differed from that of the 1957-58 Asian influenza epidemic in that the overall incidence was considerably lower (3.2%) and that the highest attack rates were not in school children but in pre-school children (71.5 per 1000 persons).Virological investigation confirmed the diagnosis of Influenza A2 infection in 56 of 63 patients (89%). Isolations were made in 29 of 51 specimens tested. Serological studies revealed that the complement fixation test was more reliable than hemagglutination - inhibition or neutralization tests. Clinical features resembled those reported in previous epidemics, cough, headache and limb pains being prominent features.     

Long-range aphid transport hypothesis for maize dwarf mosaic virus: history and distribution in Minnesota, USA

In 1977 a sudden and dramatic epidemic of maize dwarf mosaic virus (MDMV) struck commercial fields of sweet corn in Minnesota causing multi-million dollar losses. The epidemic was unusual in that MDMV historically had been confined to the southern United States and Ohio River Valley with only occasional occurrences reported from states bordering Canada. An extensive 5-yr study of MDMV in Minnesota revealed a low incidence of MDMV from 1978 - 81, and commercial fields badly infected in 1977 were not again infected. No evidence of wild host plants was found, neither was seed transmission in maize considered to be important, and MDMV strain ratios changed from year to year as did the distribution of infected fields. Concomitant studies on aphid retention revealed that MDMV could be retained by aphid vectors for more than 19 h, and that the 1977 epidemic was associated with a weather pattern that could be linked to potential aphid transport from the southern Great Plains of North America. All circumstantial evidence led to a long-distance aphid transport hypothesis. This may be worth considering whenever unexpected epidemics of aphid-transmitted non-persistent viruses occur in regions where the particular virus is not endemic, and may also explain the widespread distribution of certain aphid-transmitted non-persistent viruses.     

Epidemiologic and economic effectiveness of school closure during influenza epidemics and pandemics

Epidemiologic and economic effectiveness of school closure during influenza epidemics and pandemics is discussed. Optimal effect of school closure is observed when this measure is taken at the start of the epidemic or pandemic and for a sufficiently long time. School closure during high morbidity among schoolchildren, in the middle (at the peak) and by the end of epidemic or pandemic does not influence significantly the spread of influenza or morbidity. Significant economic losses and other negative consequences of school closure are noted. School closure may be the most appropriate during the emergence of influenza pandemic when the pandemic vaccine is not yet available, however timely mass immunization of schoolchildren against influenza may be a more appropriate measure than school closure for the reduction of influenza morbidity and spread during seasonal influenza epidemics.     

Evaluation of the efficacy of split-product trivalent A(H1N1), A(H3N2), and B influenza vaccines: protective efficacy

A total of 1,995 primary school children (1,464 vaccinees and 531 non-vaccinees) were studied to evaluate the protective efficacy of Tween-ether split trivalent A(H1N1), A(H3N2), and B influenza vaccines by comparison of the incidence of confirmed infection in two groups during 1980 to 1984. During the study period, epidemics caused by antigenically different influenza viruses, that is A(H1N1) epidemics in 1981 and 1984, a B epidemic in 1982 and an A(H3N2) epidemic in 1983, were experienced, and at the same time strains changed by antigenic drift were frequently isolated. In these epidemics, 61% to 87% of the children reported respiratory illnesses and 18% to 48% of the illnesses were influenza confirmed by seroconversion. Throughout these four epidemics, the incidence of confirmed infection among the vaccinees (7.8% to 33.8%) was 6.5% to 34.8% lower than that among the nonvaccinees (35.4% to 51.6%), demonstrating that the vaccine was effective (X2 = 76.34, P less than 0.001). However, this effectiveness was not seen in an epidemic in one of the entrant schools in 1984, possibly caused by a strain with intense antigenic drift. On the basis of data on incidence of various symptoms, duration of fever and the number of days of absence from class, it was considered that clinical symptoms in the vaccinees were milder than those in the nonvaccinees. When the titers of hemagglutination-inhibiting (HAI) antibody against the vaccine strains were measured, the protective level of HAI antibody giving less than or equal to 50% incidence of infection was 1:64, but it increased to 1:256 in the 1984 epidemic, reflecting the high rate of isolates with intense antigenic drift.     

Assessment of the prevalence of vCJD through testing tonsils and appendices for abnormal prion protein

The objective of this study was to determine the age group or groups which will provide the most information on the potential size of the vCJD epidemic in Great Britain via the sampling of tonsil and appendix material to detect the presence of abnormal prion protein (PrP(Sc)). A subsidiary aim was to determine the degree to which such an anonymous age-stratified testing programme will reduce current uncertainties in the size of the epidemic in future years. A cohort- and time-stratified model was used to generate epidemic scenarios consistent with the observed vCJD case incidence. These scenarios, together with data on the age distribution of tonsillectomies and appendectomies, were used to evaluate the optimal age group and calendar time for undertaking testing and to calculate the range of epidemic sizes consistent with different outcomes. The analyses suggested that the optimal five-year age group to test is 25-29 years, although a random sample of appendix tissue from all age groups is nearly as informative. A random sample of tonsil tissue from all age groups is less informative, but the information content is improved if sampling is restricted to tissues removed from those over ten years of age. Based on the assumption that the test is able to detect infection in the last 75% of the incubation period, zero detected infections in an initial random sample of 1000 tissues would suggest that the epidemic will be less than 870,000 cases. If infections are detected, then the model prediction suggests that both relatively small epidemics (800+ cases if one is detected or 8300+ if two are detected) and larger epidemics (21,000+ cases if three or more are detected) are possible. It was concluded that testing will be most informative if undertaken using appendix tissues or tonsil tissues removed from those over ten years of age. Large epidemics can only be excluded if a small number of infections are detected and the test is able to detect infection early in the incubation period.     

Investigation of the incidence of influenza A viraemia caused by virus strains circulating among children in 1968 - 1977.

Nineteen strains of Type A influenza virus isolated from the blood of small children in 1968--77 were studied. The investigation of the strains in HAIR with antisera to the antigenic components of the strains in HAIR with antisera to the antigenic components of the strains A/Hong-Kong/68,A/Anglia/72, A/Port Chalmers/73 and A/Victoria/75 made it possible to demonstrate antigenic "drive" of the haemagglutinin in the years 1968--1977 and to divide the strains into 4 varieties. A high sensitivity to inhibitors was observed in all the strains isolated. The study of pathogenicity and toxicity of the strains revealed viraemia in the strains isolated during the 1972--1973 epidemic and the subsequent epidemics with the absence of pathogenicity and toxicity for white mice. Regular finding of viraemia coincided in time with increased thermostablty of the haemagglutnin in the strains under study.     

Quantification of Bird-to-Bird and Bird-to-Human Infections during 2013 Novel H7N9 Avian Influenza Outbreak in China

From February to May, 2013, 132 human avian influenza H7N9 cases were identified in China resulting in 37 deaths. We developed a novel, simple and effective compartmental modeling framework for transmissions among (wild and domestic) birds as well as from birds to human, to infer important epidemiological quantifiers, such as basic reproduction number for bird epidemic, bird-to-human infection rate and turning points of the epidemics, for the epidemic via human H7N9 case onset data and to acquire useful information regarding the bird-to-human transmission dynamics. Estimated basic reproduction number for infections among birds is 4.10 and the mean daily number of human infections per infected bird is 3.16*10⁻⁵ [3.08*10⁻⁵, 3.23*10⁻⁵]. The turning point of 2013 H7N9 epidemic is pinpointed at April 16 for bird infections and at April 9 for bird-to-human transmissions. Our result reveals very low level of bird-to-human infections, thus indicating minimal risk of widespread bird-to-human infections of H7N9 virus during the outbreak. Moreover, the turning point of the human epidemic, pinpointed at shortly after the implementation of full-scale control and intervention measures initiated in early April, further highlights the impact of timely actions on ending the outbreak. This is the first study where both the bird and human components of an avian influenza epidemic can be quantified using only the human case data.     

Surveys of Respiratory Virus Antibodies in an Arctic Indian Population

A study was undertaken to determine the etiological agents responsible for epidemics in a small and relatively isolated Arctic community.Three serological surveys were carried out over a four-year period employing complement fixation tests. Clinical information from the resident nurse was also available.The results indicated that of the two clinical epidemics of “influenza” which occurred during the period of study one was due to influenza virus type A; the other was unidentified. However, influenza virus type B affected approximately 30% of the population at some time during a two-year period without being clinically recognized. An epidemic affecting mainly children, which was clinically considered to be whooping cough, was probably caused by an adenovirus. A mumps epidemic with a high attack rate for all age groups which had occurred a few months prior to the first survey was confirmed. Sendai virus and psittacosis virus are probably endemic in this community.