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.

How frequently autoantibodies against angiotensin‐converting enzyme 2 (ACE2) occur in patients infected by SARS‐CoV‐2 is understudied and limited to investigations on a small sample size. The presence of these antibodies may contribute to the long‐lasting effects of COVID‐19 observed in some individuals, particularly if IgG‐class antibodies would emerge in patients. This study assessed the prevalence of IgG autoantibodies against ACE2 in 1139 patients infected with SARS‐CoV‐2 and examined their relationship with severity, demographic characteristics, and status of vaccination against influenza. The overall prevalence of anti‐ACE IgG antibodies in our cohort was 1.5%. Most of these individuals were men (76.5%) and underwent mild COVID‐19, but some severe and asymptomatic cases were also observed. Patients with severe infection had twofold higher titers than mild and asymptomatic cases. Age, comorbidities, and influenza vaccination status were not related to antibody prevalence. The prevalence of IgG anti‐SARS‐CoV‐2 antibodies (against nucleocapsid protein and S2 subunit, but not against receptor‐binding domain) was higher in the subset with ACE2 autoantibodies. Further research is required to understand the potential spectrum and duration of effects of IgG autoantibodies against ACE2 in patients after SARS‐CoV‐2 infection, particularly concerning long COVID‐19.

Influenza surveillance was established in 1947. From this moment WHO (World Health Organization) has been coordinating international cooperation, with a goal of monitoring influenza virus activity, effective diagnostic of the circulating viruses and informing society about epidemics or pandemics, as well as about emergence of new subtypes of influenza virus type A. Influenza surveillance is an important task, because it enables people to prepare themselves for battle with the virus that is constantly mutating, what leads to circulation of new and often more virulent strains of influenza in human population. As vaccination is the most effective method of fighting the virus, one of the major tasks of GISRS is developing an optimal antigenic composition of the vaccine for the current epidemic season. European Influenza Surveillance Network (EISN) has also developed over the years. EISN is running integrated epidemiological and virological influenza surveillance, to provide appropriate data to public health experts in member countries, to enable them undertaking relevant activities based on the current information about influenza activity. In close cooperation with GISRS and EISN are National Influenza Centres--national institutions designated by the Ministry of Health in each country.

There is evidence that vaccination against seasonal influenza can improve innate immune responses to COVID-19 and decrease disease severity. However, less is known about whether it could also impact the humoral immunity in SARS-CoV-2 infected patients. The present study aimed to compare the SARS-CoV-2 specific humoral responses (IgG antibodies against nucleocapsid; anti-N, receptor binding domain; anti-RBD, subunit S2; anti-S2, and envelope protein; anti-E) between non-hospitalized, COVID-19 unvaccinated, and mild COVID-19 convalescent patients who were and were not vaccinated against influenza during the 2019/2020 epidemic season (n = 489 and n = 292, respectively). The influenza-vaccinated group had significantly higher frequency and titers of anti-N antibodies (75 vs. 66%; mean 559 vs. 520 U/mL) and anti-RBD antibodies (85 vs. 76%; mean 580 vs. 540 U/mL). The prevalence and concentrations of anti-S2 and anti-E antibodies did not differ between groups (40–43%; mean 370–375 U/mL and 1.4–1.7%; mean 261–294 U/mL) and were significantly lower compared to those of anti-RBD and anti-N. In both groups, age, comorbidities, and gender did not affect the prevalence and concentrations of studied antibodies. The results indicate that influenza vaccination can improve serum antibody levels produced in response to SARS-CoV-2 infection.

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.