Epidemiological and virological assessment of influenza activity in Europe during the winter 2005-2006

Abstract

Influenza activity in Europe during the winter 2005-2006 started late January - early February 2006 and first occurred in the Netherlands, France, Greece and England. Subsequently, countries were affected in a random pattern across Europe and the period of influenza activity lasted till the end of April. In contrast to the winter seasons in the period 2001-2005, no west-east pattern was detected. In 12 out of 23 countries, the consultation rates for influenza-like illness or acute respiratory infection in the winter 2005-2006 were similar or higher than in the winter 2004-2005, despite a dominance of influenza B viruses that normally cause milder disease than influenza A viruses. In the remaining 11 countries the consultation rates were lower to much lower than in the winter 2004-2005. The highest consultation rates were usually observed among children aged 0-14. The circulating influenza virus types and subtypes were distributed heterogeneously across Europe. Although the figures for total virus detections in Europe indicated a predominance of influenza B virus (58% of all virus detections), in many countries influenza B virus was predominant only early in the winter, whilst later there was a marked increase in influenza A virus detections. Among the countries where influenza A viruses were co-dominant with B viruses (9/29) or were predominant (4/29), the dominant influenza A subtype was H3 in seven countries and H1 in four countries. The vast majority of characterised influenza B viruses (90%) were similar to the B/Victoria/2/87 lineage of influenza B viruses that re-emerged in Europe in the winter 2004-2005 but were not included in the vaccine for the influenza season 2005-2006. This might help to explain the dominance of influenza B viruses in many countries in Europe during the winter 2005-2006. The influenza A(H3) and A(H1) viruses were similar to the reference strains included in the 2005-2006 vaccine, A/California/7/2004 (H3N2) and A/New Caledonia/20/99 (H1N1), respectively. In conclusion, the 2005-2006 influenza epidemic in Europe was characterised by moderate clinical activity, a heterogeneous spread pattern across Europe, and a variable virus dominance by country, although an overall dominance of influenza B viruses that did not match the virus strain included in the vaccine was observed.

Challenge of conducting a placebo-controlled randomized efficacy study for influenza vaccine in a season with low attack rate and a mismatched vaccine B strain: a concrete example

“…Also, all nasal and throat swab specimens were transported to the laboratory with an adequate cold chain within 24 hours to avoid false culture negatives due to loss of virus viability. Furthermore, the low attack rate observed in the study area in 2005–2006 was confirmed by the European Influenza Surveillance Scheme (EISS) [28]. Specific data for the Czech Republic demonstrate that the weekly morbidity rates for both acute respiratory infections [29] and for ILI [30] were lower in the 2005/2006 influenza season compared to both the previous 2004/2005 season and also the following 2006/2007 season.…”

“…The majority of culture-confirmed cases detected in our study were caused by an influenza B strain that was of a different lineage to the vaccine influenza B component which was from the B/Yamagata/16/88-lineage. This mismatch was confirmed by the EISS who reported that 90% of the characterized influenza B viruses in Europe during the influenza season 2005–2006 were similar to the B/Victoria/2/87 lineage of influenza B viruses [28]. As a consequence, the World Health Organization (WHO) substituted a virus from the B/Victoria/2/87 lineage in the 2006–2007 vaccine recommendations [37].…”

“…Specific data for the Czech Republic demonstrate that the weekly morbidity rates for both acute respiratory infections [29] and for ILI [30] were lower in the 2005/2006 influenza season compared to both the previous 2004/2005 season and also the following 2006/2007 season. The EISS also reported that the circulation of influenza B virus in the winter 2005–2006 was exceptional compared with European data accumulated during the last decade, as it was the only season in which influenza B viruses were dominant [28]. It is possible that this may have contributed to the low attack rate of clinical illness as influenza B is known to cause milder disease than influenza A [28,31].…”

“…The EISS also reported that the circulation of influenza B virus in the winter 2005–2006 was exceptional compared with European data accumulated during the last decade, as it was the only season in which influenza B viruses were dominant [28]. It is possible that this may have contributed to the low attack rate of clinical illness as influenza B is known to cause milder disease than influenza A [28,31]. …”

Geographic Divisions and Modeling of Virological Data on Seasonal Influenza in the Chinese Mainland during the 2006–2009 Monitoring Years

“…In related studies, the main types of seasonal influenza surveillance data used in statistical analyses are usually mortality [9], Influenza-Like Illness (ILI) and virological data [6], [10]–[12]. Alonso et al (2007) studied the seasonality of influenza throughout Brazil by modeling influenza-related mortality data from 1979 to 2001 for each of the 27 Brazilian states.…”