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.

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.

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.

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.