Influenza season 2010/11 – Norway’s risk assessment and revisited vaccine recommendationsArchived

Risk Assessment and Forecasting for the 2010/11 influenza season in Norway 

In Norway, influenza experts from the Norwegian Institute of Public Health have made a risk assessment for the remainder of the 2010/11 influenza season. Norway’s influenza vaccination recommendations have also been reconsidered. 

An important conclusion from this process is that the current situation, with B viruses dominating (80%), is likely to continue through the season. They expect that there will be around 40-50 admissions to intensive care units (ICUs) and less than 10 deaths from influenza A(H1N1)2009. Additionally they point out that, in spite of a declining prevalence of antibodies against influenza A(H1N1)2009 observed through serological surveys there is some partial herd immunity which should protect Norway from a more severe scenario. As of week 2, they have had 56 hospital admissions, 14 ICU admissions and no deaths from influenza A(H1N1). It is expected that the epidemics in Norway will peak around weeks 3 to 5 of 2011.

In more detail the Norwegian report states that the assessment teams best assessment at present for the remainder of the 2010/11 influenza season is as follows:

• Due to the level of immunity in the population, the A(H1N1)2009 virus will not cause a large wave of infections. However, it will be present as a proportion of cases throughout the whole season. This means that it may still cause some serious clinical infections. They estimate it will cause 40-50 intensive care admissions and under 10 deaths.
• A(H1N1)2009 virus has not changed significantly from 2009. It does not appear to have changed its immune profile or to cause worse symptoms. It is also not resistant to either oseltamivir or zanamivir at present.
• They expect the clinical picture in most infected cases to be the same as in 2009. This means relatively mild disease in most people, but with a more serious clinical picture in some, especially people from the recognized risk groups.
• The high level of specific immunity to A(H1N1)2009 in the population means that other viruses, principally Influenza type B virus, will infect a larger proportion of the population than might otherwise be the case. They expect the type B virus to dominate this influenza season. Type B influenza normally is associated with mild or moderate influenza seasons.
• The Norwegian Institute of Public Health will monitor closely the ongoing situation and update these predictions as needed. The report concludes that for Norway:
• The vaccination of people from risk groups should be increased as soon as possible. Others outside of these groups may also be vaccinated.
• The health services must be vigilant for the signs of severe influenza. Early antiviral treatment is important for people becoming ill from risk groups.
• Hospitals must prepare themselves to manage the treatment of numbers of patients requiring intensive care beds.
• Good surveillance is necessary and the results must be scrutinized carefully.

Revisited vaccination recommendations

In Norway, currently influenza type B viruses have dominated, however, in the last few weeks there has been an increasing proportion of A(H1N1)2009 infections. The increase in disease caused by A(H1N1)2009 has stimulated a reassessment of the current vaccine recommendations in Norway, the report of this has been published by the body leading the work, the Norwegian Institute of Public Health. The Report concluded from  the epidemiology of this influenza season so far in the Northern Hemisphere and specifically in Norway, it is likely that both the A(H1N1)2009 and influenza type B viruses will dominate this influenza season in the country. Until now in Europe, there have only been sporadic reports of cases infected with the A(H3N2) virus. The report also mentions that the stores of seasonal vaccine in Norway are only sufficient to cover those in risk groups and that it will not be possible to obtain more quantities of vaccine to cover people beyond these groups. As a consequence of this, in case they need to vaccinate a larger proportion of the population they would need to use the specific pandemic vaccine (Pandemrix). This vaccine does not provide protection against type B influenza, which is believed to be the predominant flu virus this season. The report notes that international surveillance of the side effects of Pandemrix has not led to any changes in the risk/benefit analysis for its use by EMA. The uncertainty surrounding possible links to narcolepsy in Sweden and Finland should not deter Norway from vaccination aimed at the prevention of serious influenza illness and death.

The report notes that in comparison to most other countries in Europe, Norway, Sweden and Finland are in a different situation. This is due to both the high vaccine coverage that was achieved during the 2009/10 influenza season in addition to the large number of people that were infected by the virus. This means that in all likelihood there is a high level of immunity in the Norwegian population despite the uncertainties regarding the duration of immunity conferred by one dose of the Pandemrix vaccine. Hence there should be significantly fewer sick as a result of infection with A(H1N1)2009 virus than in 2009/2010, the report states. On this basis, the working group carrying out the assessment advised not to increase the number of groups recommended for vaccination this season and to maintain the vaccine recommendations from the 29th of September 2010. Furthermore, the working group recommended to have an intensified campaign to vaccinate as many people as possible from the risk groups with this season’s influenza vaccine. In addition, it will be possible for individuals from outside the risk groups to also take the flu vaccine if so they wish. Moreover, the vaccination of people from the risk groups with the seasonal influenza vaccine is also important with regards to the Type B influenza that is expected to dominate this flu season in Norway. Finally, the working group pointed out that those from risk groups can also be protected against progression to severe disease through the early use of antivirals for the treatment of flu-like symptoms, and health professionals should be reminded of this.