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.

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.

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.

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.

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.

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.

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.

Occurrence of Influenza Hemagglutinin Antibodies in the Polish Population during the Epidemic Season 2017/18.

This study seeks to define the level of antihemagglutinin antibodies, using the hemagglutination inhibition assay (HAI), in the serum of patients, stratified into seven age groups, in Poland during the influenza epidemic season of 2017/18. A quadrivalent influenza vaccine has been introduced in Poland as of this epidemic season, making it possible for the first time to conduct the analysis for four antigens: A/Michigan/45/2015 (H1N1) pdm09, A/Hong Kong/4801/2014 (H3N2), B/Brisbane/60/2008 - Victoria lineage, and B/Phuket/3073/2013 - Yamagata lineage. We found that the level of individual antihemagglutinin antibodies was different among the seven age groups studied; with the highest in patients of 5-9 years and 10-14 years of age. Interestingly, the protection factor, defined as the percentage of people with the level of antihemagglutinin antibodies of at least 1:40 after vaccination or due to a previous infection, was the highest for the antigen A/Hong Kong/4801/2014 (H3N2) in the same age groups (74% and 75%, respectively). Taking into account the dismal 3.6% of the vaccinated population in Poland, these findings point toward the sustained presence of an immune system response in patients after a prior influenza virus 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.

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.

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.

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.

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.

Co-infection with Influenza Viruses and Influenza-Like Virus During the 2015/2016 Epidemic Season.

Concerning viral infection of the respiratory system, a single virus can cause a variety of clinical symptoms and the same set of symptoms can be caused by different viruses. Moreover, infection is often caused by a combination of viruses acting at the same time. The present study demonstrates, using multiplex RT-PCR and real-time qRT-PCR, that in the 2015/2016 influenza season, co-infections were confirmed in patients aged 1 month to 90 years. We found 73 co-infections involving influenza viruses, 17 involving influenza viruses and influenza-like viruses, and six involving influenza-like viruses. The first type of co-infections above mentioned was the most common, amounting to 51 cases, with type A and B viruses occurring simultaneously. There also were four cases of co-infections with influenza virus A/H1N1/pdm09 and A/H1N1/ subtypes and two cases with A/H1N1/pdm09 and A/H3N2/ subtypes. The 2015/2016 epidemic season was characterized by a higher number of confirmed co-infections compared with the previous seasons. Infections by more than one respiratory virus were most often found in children and in individuals aged over 65.

Circulation of Antibodies Against Influenza Virus Hemagglutinins in the 2014/2015 Epidemic Season in Poland.

The aim of this study was to determine the level of anti-hemagglutinin antibodies in the serum of people in different age-groups during the 2014/2015 epidemic influenza season in Poland. A total of 1050 sera were tested. The level of anti-hemagglutinin antibodies was determined using the hemagglutinin inhibition test. The results provided information on the incidence of circulating A/California/7/2009(H1N1)pdm09, A/Texas/50/2012(H3N2), and B/Massachusetts/2/2012 viruses. The level of antibodies against influenza differed between age-groups. The protection rate was the highest for the antigen B/Massachusetts/2/2012, with the decreasing order of values in the following age-groups: ≥65 years (76.7 %), 15-25 years (72.7 %), and 0-4 years (62.0 %). The average values of the protection rate in other age-groups were as follows: 43.3 % in 22-64 years, 40% in 5-9 years, and 39.3 % in 45-64 years of age, while the lowest value of 22.7 % was in 10-14 years old subjects. In the 2014/2015 epidemic season in Poland only were 3.6 % of the population vaccinated. That is why the presented results could be interpreted as a response of the immune system of patients after infection caused by influenza virus.

The Activity of Influenza and Influenza-like Viruses in Individuals Aged over 14 in the 2015/2016 Influenza Season in Poland.

Infections in every epidemic season induced by respiratory viruses, especially by the influenza virus, are the cause of many illnesses and complications which often end in death. The aim of this study was to determine the activity of influenza and influenza-like viruses in individuals aged over of 14 in Poland during the 2015/2016 epidemic season. A total of 5070 specimens taken from patients were analyzed. The presence of the influenza virus was confirmed in 40.2% of cases, among which the subtype A/H1N1/pdm09 (62.6% positive samples) predominated. The analysis of confirmed influenza and influenza-like viruses in individuals divided into four age-groups demonstrate that the highest morbidity was reported for the age ranges: 45-64 (13.1%) and 26-44 (12.6%) years. An increase in the number of influenza type B cases (23.7% positive samples), which was the main cause of morbidity in the age group 15-25 years, was noticeable. Given the epidemiological and virological data, the 2015/2016 season in Poland was characterized by increased activity of the influenza virus compared to the previous season. In the 2015/2016 season, there were more than 3.8 million cases and suspected cases of influenza and influenza-like illness, more than 15,000 hospitalizations, and up to 140 deaths.

Influenza and Influenza-like Viruses in Children in the Epidemic Season 2015/2016 in Poland.

Influenza is an infectious disease caused by influenza A and B viruses. Children are the group which is the most exposed to influenza and influenza-like infections. They are considered as carriers of influenza infections in the population. In the epidemic season 2015/2016 more than 8000 samples were tested, of which over 30 % specimens were collected from patients aged 0-14 years. In 42.3 % cases the influenza or influenza-like viruses were confirmed. The most common subtype was A/H1N1/pdm09. Analysis of positive specimens was categorized into three smaller groups 0-4, 5-9, 10-14. Differences in the frequency of virus detections in younger age groups appeared. This study has shown that children are a very important group in the spread of the influenza virus in the population. A higher percentage of vaccinated children would decrease the number of infected patients in the whole population.

Regional Diversification of Influenza Activity in Poland During the 2015/16 Epidemic Season.

The National Influenza Center (NIC) at the Department of Influenza Research of the National Institute for Public Health-National Institute of Hygiene (NIPH-NIH) participates in the Global Influenza Surveillance and Response System (GISRS) and continuously coordinates epidemiological and virological surveillance of influenza in Poland. The aim of this study was to determine the regional differences of influenza activity in Poland in the 2015/16 epidemic season. The influenza surveillance involved 16 administrative districts in which there are Voivodeship (province) Sanitary Epidemiological Stations set up to report influenza and influenza-like illness among the Polish population. Over 8000 specimens were tested in the season with regard to the respiratory viral infections in all regions investigated. The circulation of influenza viruses A and B was confirmed, with the subtype A/H1N1/pdm09 being predominant in the Pomerania, Podlaskie, Subcarpathian, Lubuskie, Silesian, and Warmian-Masuria provinces. The influenza-like virus occurred in individual cases, except for respiratory syncytial virus that also was detected in the Greater Poland and Warmia-Masuria provinces. The highest incidence of cases and suspected cases of influenza was recorded in Pomerania and the lowest one in Lubuskie provinces. The knowledge of regional differences in influenza activity is important for streamlining the distribution of preventive, therapeutic, and economic resources to combat the epidemic.

The Sentinel System as the Main Influenza Surveillance Tool.

Poland has implemented the influenza surveillance system called Sentinel as of 2004. The system consists of both epidemiological and virological surveillance. It is an important tool for monitoring the situation in the entire country, coordinated by the National Influenza Center situated at the National Institute of Public Health-National Institute of Hygiene (NIPH-NIH) in Warsaw, Poland. In the 2015/2016 epidemic season, more than 1600 samples were tested in the Sentinel System, of which 38.6% were positive. The samples were evaluated in seven age-groups: 0-4, 5-9, 10-14, 15-25, 26-44, 45-64, and over 65 years of age. Significant differences were reported in the number of confirmed cases of infection caused by influenza and influenza-like viruses, depending on the age-group. The highest number of confirmed cases of infections was reported for the age range of 26-44 years, accounting for 30% of the total. In each age-group, the presence of infection caused by influenza-like viruses, collectively accounting for only 3.8% of all positive tests, was also confirmed. Weekly reports generated by the Sentinel System enable to determine and control a current influenza activity in the country, which is of essential importance in case of the emergence of a new strain with a pandemic potential.