Regional Activity and Spread of Influenza Viruses in Poland in the Context of Neighboring Countries in the Epidemic Season 2017-2018: An Epidemiological Review.

This article reviews the epidemiological situation in Poland during the 2017-2018 influenza season in the context of viral spread from the neighboring countries. There were 5793 specimens tested for the presence of influenza virus. The specimens were collected from patients with suspected upper airway infection. The presence of influenza virus was confirmed in 2454 specimens. The data were used to determine the extent of morbidity and the possible direction of spread of influenza virus. It was found that virus type B predominated in 13 out of the 16 Polish provinces, type A predominated in just 1 province, and both types predominated equally in another 2 provinces. Data on influenza type B virus did not enable the drawing of a clear-cut conclusion on the way of its spread. Presumptively, the route of type B virus spread originated in the Ukraine and moved westward, with the transmission enhanced, to some extent, by migration of Ukrainian citizens. Virus type A, on the other side, spread from the Southwest Europe eastward. Reviewing the epidemiological situation plays an important role in gaining more knowledge on influenza morbidity and its differentiation from other similar infections, which helps counteract future infections.

Virological and Epidemiological Situation in the Influenza Epidemic Seasons 2016/2017 and 2017/2018 in Poland.

The World Health Organization estimates that influenza virus infects 3-5 million people worldwide every year, of whom 290,000 to 650,000 die. In the 2016/2017 epidemic season in Poland, the incidence of influenza was 1,692 per 100,000 population. The influenza A virus, subtype A/H3N2/, was the predominant one in that season. However, in the most recent 2017/2018 epidemic season, the incidence exceeded 1,782 per 100,000 already by August of 2018. In this season, influenza B virus predominated, while the A/H1N1/pdm09 strain was most frequent among the influenza A subtypes. The peak incidence, based on the number of clinical specimens tested, was in weeks 4-5 of 2017 and week 8 of 2018 in the 2016/2017 and 2017/2018 epidemic seasons, respectively. As of the 2017/2018 season, a quadrivalent vaccine, consisting of two antigens of influenza A subtypes and another two of influenza B virus, was available in Poland. Nonetheless, the vaccination rate remained at one of the lowest level in Europe, fluctuating between 3% and 4% of the general Polish population.

Respiratory Virus Infections in People Over 14 Years of Age in Poland in the Epidemic Season of 2017/18.

People most at risk of influenza complications are the elderly with impaired immunity. Clinical picture of influenza virus infection includes symptoms such as chills, increased body temperature, dry cough, chest pain, or dizziness as well as headaches and muscle aches. In the diagnosis of influenza, quick and effective tests are necessary. Sensitive diagnostic methods of molecular biology require more time, but the result firmly confirm or exclude the presence of the genetic material of influenza or other respiratory viruses. Influenza vaccination plays an important role in combating influenza infection. Unfortunately, the awareness of vaccination benefits is insufficient in Poland. In this study we demonstrate the results of examination of 4,507 people aged over 14 years toward the influenza infection in the epidemic season of 2017/18. Most of the confirmed infections were reported in older people aged over 65, a high-risk population group. A low percentage of the vaccinated population may affect an increased number of confirmed influenza viruses in the elderly. The findings demonstrate a need to increase awareness of vaccination benefits, which is particularly essential to avoid influenza infection in the elderly.

Evaluation of the 2017/18 Influenza Epidemic Season in Poland Based on the SENTINEL Surveillance System.

The SENTINEL influenza surveillance system is an important tool for monitoring influenza in Poland. Data from this system are necessary to determine the dynamics of seasonal infections and to announce the epidemic by the country level. For the 2017/18 epidemic season, the dominance of influenza type B was recorded and the highest percentage of infections was recorded in the age group 45-64 years. Among the subtypes of influenza type A, A/H1N1/pdm09 was the predominated subtype. Most cases were reported in the age group of 26-44 and 0-4 years. The influenza virus frequently undergoes modifications. Therefore, it is necessary to constantly monitor the emerging strains around the world.

Infections Caused by Influenza Viruses Among Children in Poland During the 2017/18 Epidemic Season.

Influenza is an infectious disease that is a threat to both children and adults. The most effective way to prevent infections among children is seasonal vaccination in every epidemic season, which is recommended from the age of 6 months onward. This study is a report of the prevalence of influenza infection in the population of children up to the age of 14 years and of the type of influenza virus involved during the 2017/18 epidemic season in Poland. We found that influenza A and B viruses co-dominated in the season. Among the influenza A viruses, A/H1N1/ pdm09 subtype was a more frequent source of infection than A/H3N2/ subtype. In addition, the prevalence of infection was re-analyzed in children stratified into the age groups of 0-4, 5-9, and 10-14 years old. We found a relation between the age of a child and the type of influenza virus causing infection. The youngest children under 4 years were the most vulnerable to both influenza and influenza-like infections; the former caused mostly by influenza A and the latter by RSV. In contradistinction, influenza B dominated in the oldest children aged 10-14 and RSV infections were not present in this age group. The characteristics of influenza viruses may however vary on the seasonal basis.

Circulation of Influenza Virus in the 2015/2016 Epidemic Season in Poland: Serological Evaluation of Anti-hemagglutinin Antibodies.

The diagnostic of influenza virus infections is possible using molecular biology methods as well as the analysis of anti-hemagglutinin (anti-HA) antibodies in the blood serum. The aim of this study was to determine the level of anti-HA antibodies in 7 age groups of patients during the 2015/2016 epidemic season in Poland. A total of 1050 serum samples were tested using the hemagglutination inhibition (HAI) assay. We confirmed the presence of anti-HA antibodies for the influenza virus strains: A/California/7/2009(H1N1)pdm09, A/Switzerland/9715293/2013(H3N2), and B/Phuket/3073/2013, which were the components of the influenza vaccine for the 2015/2016 epidemic season. The level of specific anti-HA antibodies was different in each age group. The geometric mean titers were highest at age 5-9 years, where the antibody protection level reached 61.3% against B/Phuket/3073/2013 and 52.7% for A/Switzerland/9715293/2013(H3N2) antigen. The antibody level amounted to 56.7% against for antigen B at age 45-64. In the remaining age groups, the protection levels for all hemagglutinin types did not exceed 50%. These findings confirm the urgent need to increase a persistently low influenza vaccination coverage in the Polish population, which may have had its part in the noticeable increase in the confirmed cases of influenza and influenza-like virus infection during the season.

Respiratory Viruses in Different Provinces of Poland During the Epidemic Season 2016/2017.

In Poland, influenza surveillance is conducted by 16 Provincial Sanitary Epidemiological Stations, headed by the Department of Influenza Research, National Influenza Center at the National Institute of Health - National Institute of Hygiene (NIPH-NIH). During the epidemic season 2016/2017, more than 4000 samples were tested for respiratory infections, with approximately 1800 positive results, the most of which were among patients over 65 years old. Most samples were tested in the Western Pomeranian province, but the greatest proportion of positively diagnosed influenza infections, amounting to 72.7% was noted in the Lodz metropolitan area in central Poland. Twenty five deaths due to post-influenza infections and complications were recorded across the country, of which 20 were among individuals over 65 years of age. During the 2016/2017 season, the dominant subtype was A/H3N2/, unlike the subtype A/H1N1/California/7/2009 during the previous season. A high number of confirmed infections of subtype A/H3N2/can attest to low vaccination rates.

Detection of Influenza in the Epidemic Season 2016/2017 Based on I-MOVE+ Project.

In the influenza season 2016/2017 in Europe, the predominant virus was A/H3N2/. In Poland, the percentage of people vaccinated against influenza was 3.33%. European I-MOVE+ project shows how important it is to monitor the effectiveness of influenza vaccine. The project demonstrates that a match between the circulating vaccine strains and those included in the vaccine for the Northern Hemisphere was low-to-moderate. In the present study, there were 379 patients and 296 control subjects examined in hospitals in Poland as part of I-MOVE+ project. The real-time reverse transcription polymerase chain reaction (qRT-PCR) method was used to detect the influenza virus in all subjects. We detected the influenza subtype A/H3N2/ in 59.1% and type B virus in 2.1%. There was one co-infection of subtype A/H3N2/ with subtype A/H1N1/ and eight co-infections of type B with subtype A/H3N2/. No influenza viruses were detected in the control group. Only 19 patients and 22 control subjects were vaccinated during the epidemic season in question. A proportion of people vaccinated against influenza in Poland remains dismally low compared to other European countries.

Influenza and Influenza-Like Viruses: Frequent Infections in Children Under 14 Years of Age During the 2016/2017 Epidemic Season.

Influenza is an infectious disease that is a common cause of infection among children. The main reason for it is the extremely low percentage of vaccinated people in Poland. In the 2016/2017 epidemic season more than 3,000 tests from children up to age 14 were examined. The dominance of subtype A/H3N2/ (40.9%) was confirmed. The evaluation was stratified by three age groups (0-4, 5-9, and 10-14 years), which revealed significant differences. The highest number of samples was available in the 0-4 years group. The highest percentage of positive samples was present in the 10-14 years group. Influenza-like viral infections, among them the respiratory syncytial virus, were also observed. Children due to immature immunity are at particular risk for influenza. A lack of proper vaccination coverage strongly increases the chance of serious complications of the infection.

Infections with Influenza A/H3N2/ Subtype in Poland in the 2016/2017 Epidemic Season.

The 2016/2017 epidemic season was characterized by a lower number of diagnostically tested samples of the nasal and throat swabs and bronchoalveolar lavage fluid, compared with the preceding season. The predominant influenza subtype found was A/H3N2/ which was notably diagnosed in patients over 25 years of age. This subtype was also often diagnosed in older people of 65+ years, which is in line with the risk assessment prepared by the European Center for Disease Prevention and Control (ECDC) at the beginning of the season. The A/H3N2/ subtype was most often diagnosed in the West Pomeranian and Warmian-Masurian Voivodeships. In this epidemic season, there were 11 coinfections of the A/H3N2/ subtype with other influenza and influenza-like viruses recorded in Poland. A different situation had occurred in the 2014/2015 season, when the subtype A/H3N2/ also was predominant, but the virus was most commonly diagnosed in children up to 14 years of age. In both seasons, the least confirmations were observed in patients between 15 and 24 years.

Antibodies to Influenza Virus Hemagglutinin in the 2016/2017 Epidemic Season in Poland.

The aim of the study was to determine the level of antibodies against hemagglutinin of influenza viruses in the sera of 1,050 patients stratified into 7 different age groups during the 2016/2017 epidemic season in Poland. The method consisted of using the hemagglutination inhibition test (HAI). The findings confirmed the presence of anti-hemagglutinin antibodies against the following influenza virus antigens: A/California/7/2009 (H1N1) pdm09, A/Hong Kong/4801/2014 (H3N2), and B/Brisbane/60/2008. The level of anti-hemagglutinin antibodies differed across the age groups investigated, with the highest values in patients aged 10-14 years. We also found that the protection factor was highest for B/Brisbane/60/2008 antigen. It amounted to 72.7% in 10-14-year olds and to 69.3% in both 15-25 and 26-44-year olds. Taking into account a dismally low percentage of vaccinated population in the 2016/2017 epidemic season in Poland, amounting to barely 3.33%, the findings should be interpreted as representing the patients' immune system response to influenza virus infection.

Virological Situation in Poland in the 2016/2017 Epidemic Season Based on Sentinel Data.

The influenza Sentinel surveillance system is a source of valuable data about the dynamics of epidemic seasons in Poland. During the epidemic season 2016/2017, more than 1,000 samples were examined, of which 48% were positive for influenza diagnosis. The predominance of influenza A/H3N2/ was confirmed. Influenza B viruses were noted in only 1% of the samples tested. After the analysis in age groups, the highest number of positive samples was observed in the group of 26-44 years. Infections caused by influenza-like viruses were confirmed only in 3% of cases. The Sentinel surveillance system makes it possible to evaluate the spread of the influenza virus in each epidemic season.

Respiratory Infections with Particular Emphasis on Influenza Virus Activity in Persons Over 14 Years of Age in the Epidemic Season 2016/2017 in Poland.

Influenza viruses cause respiratory infections every epidemic season regardless of the patient's age. The aim of this study was to determine the activity of respiratory viruses in the epidemic season 2016/2017 in Poland, with particular emphasis on influenza viruses among people aged over 14. There were 2982 clinical samples taken from patients from four age groups: 15-25, 26-44, 45-64, and ≥ 65 years tested under the Sentinel and non-Sentinel surveillance programs. The presence of influenza viruses was confirmed in more than 40% of cases, the predominant type was influenza A virus unsubtyped, followed by subtype A/H3N2/. The results for the four age groups indicate that the highest number of confirmed respiratory viruses was recorded in individuals ≥65 years of age, slightly less, in the decreasing order, in the age groups 45-64 years, 15-25 years, and 26-44 years. Influenza type B infections were observed only in sporadic cases. Given the epidemiological data, epidemic season 2016/2017 was characterized by similar dynamics compared to the previous season in Poland and also in most of the European countries. More than 4 million cases and suspected cases of influenza and influenza-like viruses have been reported in Poland, more than 16,000 hospitalizations, and 25 deaths, of which 20 cases occurred among people ≥65 years of age in the epidemic season 2016/2017.

Virological Characteristics of the 2014/2015 Influenza Season Based on Molecular Analysis of Biological Material Derived from I-MOVE Study.

The main goal of the international study I-MOVE (Influenza Monitoring of Vaccine Effectiveness) implemented in Poland is to identify and evaluate the activity types of influenza virus and to determine the effectiveness of vaccination against influenza in the 2014-2015 influenza season. The study is based on selecting patients with flu symptoms and collecting biological samples for laboratory examination. Detection, typing, and subtyping of influenza viruses were carried out by the National Center for Influenza Virus Research at National Institute of Public Health - National Institute of Hygiene, serving as a reference center, and also in selected laboratories of the Regional Sanitary Epidemiological Stations. Molecular biology methods, such as reverse transcription polymerase chain reaction (RT-PCR), were applied in this study. A total of 218 samples were collected. A hundred and twenty six samples, representing 57.8 % of the total, were confirmed with influenza virus infection. Influenza type A virus was detected in 54 samples, which included 16 samples of A/H1N1/pdm09 subtype and 11 samples of A/H3N2/ subtype. The remaining 27 samples positive for influenza type A were not subtyped. Influenza type B virus was detected in 57 samples, which appeared to be the dominant strain in this study. Furthermore, several cases of concurrent infection with influenza type B virus and the A/H1N/pdm09 or A/H3N2/ subtype were observed.

Antigenic Drift of A/H3N2/Virus and Circulation of Influenza-Like Viruses During the 2014/2015 Influenza Season in Poland.

Morbidity rates of influenza could be greatly reduced due to vaccination. However, the virus is able to evolve through genetic mutations, which is why vaccines with updated composition are necessary every season. Their effectiveness depends on whether there is a good antigenic match between circulating viruses and vaccine strains. In Poland, the 2014/2015 influenza epidemic started in week 5 (January/February) of 2015 and continued until week 17 (April) of 2015. The influenza activity was moderate with the highest incidence of influence-like illness at week 10/2015 (March). During that season, antigenic drift of influenza virus A/H3N2/ occurred causing higher rates of A/H3N2/ infections. Among the 2416 tested specimens, 22.6 % of influenza cases were positive for A/H3N2/, while A/H1N1/pdm09 constituted 14.6 % cases. Influenza A viruses were detected in co-circulation with influenza B viruses; the latter amounted to 34.1 % of all influenza detections. Other detected causes of influenza-like illness consisted of respiratory syncytial virus (RSV), being predominant, and, sporadically, human coronavirus, parainfluenza 1-3, rhinovirus, and adenovirus. Despite low vaccine effectiveness of solely one component, A/H3N2/, the vaccine could mitigate or shorten the length of influenza infection and reduce the number of severe outcomes and mortality. Thus, vaccination against influenza remains the most effective way to prevent illness and possibly fatal outcomes.

Viral Infections in Children in the 2014/2015 Epidemic Season in Poland.

In every epidemic season, viral infections affect the general population, including children, which is an underestimated issue. The present study demonstrates the results of examination of 802 clinical samples obtained from pediatric patients aged 0-14 years during the 2014/2015 epidemic season in Poland. The study was part of the virological surveillance systems - SENTINEL and NON-SENTINEL. A positive result for virological infection was obtained in 50.9 % of samples tested. The distribution of positive results by the age-groups was as follows: 38.2 % in 0-4 years old, 8.5 % in 5-9 years old, and 4.2 % in 10-14 years old children. Influenza viruses accounted for 48.0 % and influenza-like viruses for 52.0 % of all positive samples. Concerning the influenza virus, molecular biology-based techniques confirmed the infection caused by influenza type A in 63.3 % of samples, consisting of unsubtyped A virus detected in 65.3 % of cases of this sample group, subtype A/H1N1/pdm09 in 28.2 %, and subtype A/H3N2/ in 6.5 %. Genetic material of influenza B was detected in 36.7 % of samples. In a group of influenza-like viruses, the predominant virus was respiratory syncytial virus (RSV) in as many as 96.2 % of samples, followed by parainfluenza viruses: PIV3 - 1.4 % and PIV1 - 1.0 %. Attention should be paid to the coinfection of respiratory viruses. There were six possible coinfection combinations reported in Poland, with four of them related to children up to 14 years old.

Molecular Characteristics of Influenza Virus Type B Lineages Circulating in Poland.

From the time of the Hong Kong pandemic of 1968-1969, vaccines against influenza are trivalent, containing two subtypes of influenza type A: A/H1N1/ and A/H3N2/, and influenza type B. In 1980, circulation of the new Yamagata and Victoria lineages of influenza B virus was noted. Since both lineages have continued to circulate, the second lineage of influenza B was included into the trivalent vaccine as of the 2013/2014 epidemic season. In Poland, co-circulation of influenza type A and B has been registered over many seasons, although type A has predominated. According to the ACIP recommendations, quadrivalent vaccines against influenza are administered in some continents due to circulation of the B-Yamagata and B-Victoria lineages. Currently, only trivalent vaccines against influenza are available in Poland. The aim of the present research was to determine which of the two influenza type B lineages, or possibly both, would be isolated in Poland. The study was conducted with the use of RT-PCR. Generally, in the 2014/2015 epidemic season in Poland, circulation of type B virus was confirmed in 34 % of influenza cases. A total of 89 specimens of influenza B were tested, including co-infections of influenza B with influenza A subtypes: A/H1N1/pdm09 and A/H3N2/. The findings were that only lineage B-Yamagata circulates in the Polish population. Therefore, vaccines available on the Polish market do not require the introduction of a fourth component.

Incidence of Circulating Antibodies Against Hemagglutinin of Influenza Viruses in the Epidemic Season 2013/2014 in Poland.

The aim of this study was to determine the level of antibodies against hemagglutinin of influenza viruses in the sera of people in different age groups in the epidemic season 2013/2014 in Poland. The level of anti-hemagglutinin antibodies was determined by hemagglutination inhibition test (HAI). A total number of 1,050 randomly selected sera was tested in seven age groups. The level of antibodies against influenza viruses was very low, which indicates that the people have not been vaccinated against influenza in the epidemic season 2013/2014. The value of protection rate against influenza in the Polish population is very low. These results are worrying, because complications of influenza may be harmful to health and even life-threatening to persons who are not vaccinated. Furthermore, these results confirm the circulation of three antigenically different influenza virus strains, two subtypes of influenza A virus--A/California/7/2009/(H1N1)pdm09 and A/Victoria/361/2011(H3N2)--and B/Massachusetts/2/2012.

Evaluation of the Activity of Influenza and Influenza-Like Viruses in the Epidemic Season 2013/2014.

Infections caused by respiratory viruses can have different clinical symptoms, while specific set of symptoms can be induced by different viruses. Despite usually mild course of disease, some viruses causing certain disease entity can result in serious complications. Therefore, quick and appropriate diagnostic is crucial for administering proper treatment. In the epidemic season 2013/2014, 2,497 specimens were tested. Infections caused by influenza viruses were confirmed in 9.8%, while infections caused by influenza-like viruses (ILI) in 13.2%. The co-domination of A/H1N1/pdm09 (29.4%) with A/H3N2/ (30.6%) was observed among circulating subtypes of influenza virus type A. Analysis of positive specimens categorized into 7 age groups indicated that most of morbidity to influenza was noted in the age intervals: 26-44 (22.9%) and 45-64 years old (21.6%). Considering infections caused by influenza-like viruses, the highest amount of positive cases was registered in the age group 0-4 years old (92.7%) with the highest ratio of RSV (87.9%) and PIV-3 (10.5%). Judging by the epidemiological and virological indicators, the 2013/14 influenza season was mild and only low virus activity was reported in Poland as well as in most European countries. Still, 9,000 hospitalizations and 17 deaths were registered in Poland during this epidemic season.

Vaccination status and perception of influenza vaccination in the Polish population.

Influenza is still considered to be the most dangerous infectious disease of the twenty-first century. Outbreaks of influenza occur worldwide and affect all ages. The disease is severe, often with threatening complications and can lead to death, albeit many people have it in disregard. One of the main ways of preventing the disease is vaccination. The most effective method of prevention against influenza illness and its complications are annual vaccinations. Vaccinations, although recommended by the Ministry of Health in Poland, are not subject to refund. This paper presents the results of research conducted with the use of an anonymous questionnaire containing 18 questions to be completed by parents of school children, students of technical and medical universities, patients, medical staff, and people over 65 years of age. The study was conducted in the season of 2012/2013 in Poland. The survey involved 1,203 people in various age groups with different educational background. The analysis of the study shows that respondents very rarely use this form of prevention. Even if the vaccination were refunded, the percentage of people vaccinated against influenza would not increase significantly. Among the respondents, those who are in favor of influenza vaccination are in the minority.