Report on the Epidemiology of Influenza in Germany 2018/2019

Executive Summary

>> full report in German

The information on the epidemiology of influenza in Germany for the 2018/19 season is mainly based on the analysis and assessment of data collected by the Robert Koch Institute’s (RKI) various surveillance systems for the monitoring of acute respiratory infections (ARI), particularly influenza, in Germany. The national sentinel system of the Working Group on Influenza (AGI) with its syndromic surveillance of acute respiratory diseases and the virological surveillance of respiratory pathogens continues to be a central instrument in the overall concept of influenza surveillance in Germany. The virological data of the AGI on influenza are supplemented by results of six state laboratories cooperating with AGI in Baden-Württemberg, Bavaria, Mecklenburg-Western Pomerania, Saxony, Saxony-Anhalt and Thuringia. Mecklenburg-Western Pomerania contributed syndromic data from sentinel practices of the state’s own surveillance. The National Influenza Center (NIC) conducted additional virological analyses of circulating influenza viruses and the consultant laboratory for RSV, parainfluenza viruses and metapneumoviruses added characterisation results for RSV. Mandatory reports of laboratory confirmed cases of influenza were obtained from the German local health authorities who submitted notifications via state health authorities to the RKI. These were also included in the report, as were the results from the web-based participatory surveillance system GrippeWeb where 14,000 participants are registered. Finally we present results from the electronic module of the AGI (SEEDARE), the hospital surveillance system for severe acute respiratory infections (ICOSARI) and timely mortality data from the federal states Berlin and Hesse.

This season we identified the first influenza viruses, namely A(H3N2) viruses, within the AGI sentinel in the 44th calendar week (CW) 2018. In the 2nd CW 2019 the proportion of influenza-positive samples (positivity rate) rose to 18 %. Thus, in the 2018/19 season the flu epidemic began in the 2nd CW and it ended in the 14th CW 2019 in early April. The activity of acute respiratory diseases, measured by the so called practice index, reached values of high ARI activity from CW 6 to 8 2019. However, the values of the practice index during the peak of the flu epidemic in the 8th and 9th CW 2019 remained below the values of the last two seasons.

We estimate that a total of approximately 3.8 million influenza-attributable medically attended acute respiratory illnesses (iMAARI) occurred (95 % confidence interval (CI), 3.0 – 4.6 million), including approximately 2 million iMAARI by influenza A(H1N1)pdm09 and around 1.8 million iMAARI through influenza A(H3N2). Especially at the beginning of the flu epidemic, there was an overlap with MAARI, especially in infants, who were caused by RSV. Around one million rMAARI in the 2018/19 season were attributed to this pathogen. Influenza-associated (physician certified) incapacities for work (or the need for bed rest in patients who do not need a sick leave note) were estimated at 2.3 million (95 % CI 2.1 – 2.5 million). The estimated number of influenza-related hospitalizations from primary care practices was 18,000 (95 % CI 16,000-20,000).

Compared with previous seasons, the estimate for iMAARI is therefore significantly lower than in the extraordinarily severe flu epidemic in the 2017/18 season and the severe seasons 2012/13 and 2014/15. The estimate for influenza-attributable hospital admissions is also lower than the estimates for 2016/17 and 2017/18, roughly comparable to the values for the 2015/16 season.

As in the previous season, the number of laboratory-confirmed hospitalised influenza cases reported through the mandatory reporting system exceeded the AGI estimate, likely because the latter is restricted to hospital admissions from GP or pediatric practice and does not include – for example – direct admissions through the emergency care system.

For the 2018/19 season, no estimate of excess-mortality could be made, as the necessary data of the Federal Statistical Office are published with a time delay. However, the estimate for the 2017/18 season (still lacking in the last annual report) has been supplemented: approximately 25,000 influenza-related deaths exemplify – together with other parameters – the extraordinary severity of the flu epidemic 2017/18.

According to the virological sentinel surveillance conducted by the NIC influenza A(H1N1)pdm09 and A(H3N2) viruses co-circulated during the flu epidemic from the start. Since the end of February influenza A(H3N2) viruses dominated. In total, 51 % influenza A(H1N1)pdm09 and 49 % influenza A(H3N2) viruses were detected. Influenza B viruses circulated only sporadically during the 2018/19 season, and were not identified in the sentinel. The influenza A(H1N1)pdm09 viruses reacted well with post-infection ferret antiserum raised against the respective vaccine viruses and with the vaccine strains recommended for the upcoming 2019/20 season. For the A(H3N2) viruses the antigenic analysis showed no good agreement with the vaccine strains. The NIC also conducted molecular analyses of influenza-positive samples in the context of the investigation and management of influenza outbreaks conducted by local health authorities where also severe cases had occurred. In addition, samples were analysed that were sent to the NIC coming from other patients with a severe or fatal course. Finally, the NIC had also tested approximately 36 % of the influenza viruses for resistance against antivirals. Except for one influenza A(H1N1)pdm09 virus, where resistance may have occurred under therapy, all viruses tested were susceptible to the neuraminidase inhibitors oseltamivir, zanamivir and peramivir. The influenza viruses examined were also sensitive to the antiviral drug baloxavir marboxil, which has not yet been licensed in the EU. The RSV characterized by the consultant laboratory belonged with more than 60 % to group B (as was the case in the 2017/18 season), while in the 2016/17 season RSV group A viruses dominated with about 60 %.

The analysis of the GrippeWeb data shows that the ILI rates in the 2018/19 influenza season were similar to an averaged course based on data from the years 2011 to 2018. In this report we show also the proportion of patients with ARI or ILI symptoms who visit a physician because of the symptoms.

The distribution of the ICD-10 diagnostic codes for ARI in ambulatory care is shown in the more detailed analysis of the SEEDARE data. The number of consultations in which certain ICD-10 codes for upper respiratory tract infections, influenza or lower respiratory tract infections have been used, showed a clear seasonal pattern. In the 2018/19 season, it was noticeable that especially infants were seriously ill and a higher proportion as usual was hospitalized. Using the case-based anonymous information from the SEEDARE module, further respiratory syndromes can also be specifically analysed, such as illnesses that have been coded as community-acquired pneumonia.

For the assessment of progression to severe disease, valuable information was obtained in the context of the ICD-10 code based syndromic hospital surveillance for severe acute respiratory infections (ICOSARI) in the 2018/19 season. The number of hospitalized SARI patients was significantly lower than in the 2017/18 season, but high SARI case numbers in the 0- to 4-year age group were again documented.

In the timely analysis of excess mortality during the season, the report presents the estimates for the states Berlin and Hesse. Here too, the estimates were lower than in the more severe seasons 2016/17 and 2017/18.

The World Health Organization’s (WHO) annual recommendations on influenza vaccines, the recommendations of the German Standing Committee on Vaccination (STIKO), and the assessment of the influenza vaccine effectiveness for the 2018/19 season are all presented in the chapter »Influenza Vaccination«. For the 2019/20 season, the WHO recommended a different composition of the influenza vaccine for the influenza A(H1N1)pdm09 and the A(H3N2) components in comparison to the Northern Hemisphere 2018/19 season:

an A/Brisbane/02/2018 (H1N1)pdm09-like virus (new);

an A/Kansas/14/2017 (H3N2)-like virus (new);

a B/Colorado/06/2017-like virus (Victoria lineage) unchanged; and

a B/Phuket/3073/2013-like virus (Yamagata lineage) unchanged.

As in the previous seasons, the effectiveness of influenza vaccination in the 2018/19 season was assessed by analysing the virological surveillance data of the AGI. The overall effectiveness of seasonal influenza vaccine against laboratory-confirmed influenza disease was low, however, effects differed by subtype: effectiveness against influenza A(H1N1)pdm09 disease was high, while no effectiveness was shown against laboratory confirmed influenza A(H3N2) disease.

Lastly, the chapter on zoonotic influenza describes the situation on avian and porcine influenza in their respective animal species, as well as in humans. As in previous years, no human case with zoonotic influenza virus infection was reported in Germany. However, also in the 2018/19 season, human infections with avian and porcine influenza viruses occured worldwide. They were mostly attributed to exposure to infected animals. There was also no evidence of sustained human-to-human transmission with these zoonotic influenza viruses.As long as the influenza viruses circulate in livestock, sporadic human infections may continue to occur.