January 16, 2018

Q&A on winter flu outbreak

There is an ongoing outbreak of flu in the UK, which has resulted in hospitalisations and some deaths.

What strains of flu are circulating this year?

Public Health England has reported an increase in the levels of influenza in the community and this increase has also been seen in Scotland and in Northern Ireland. Influenza A and influenza B viruses are circulating. The predominant influenza A viruses are of the H3N2 subtype and influenza B viruses of the B/Yamagata lineage are the predominating influenza B viruses. In Scotland and Northern Ireland, the number of influenza A infections has been greater than influenza B inflections but in England and Wales currently the proportions of influenza A viruses and influenza B viruses are similar.

Are they strains we normally get or new strains?

Influenza H3N2 viruses predominated in the winters of 2014/2015 and 20216/2017 and in each of  these two winters influenza had a considerable impact. The H3N2 viruses were are seeing in the Northern Hemisphere are similar to those seen in Australia and Hong Kong in the months of June through to August last year (2017) which, in turn, were not markedly different from those seen in the Northern Hemisphere in the early months of 2017.

The influenza B viruses of the B/Yamagata lineage are similar to the virus present in quadrivalent influenza vaccines, including the Live Attenuated Influenza Vaccine used for children.

What is Aussie flu? Do we normally get it in winter or is it new?

The H3N2 viruses were are seeing in the Northern Hemisphere are similar to those seen in Australia and Hong Kong in the months of June through to August last year (2017) which, in turn, were not markedly different from those seen in the Northern Hemisphere in the early months of 2017.

The analyses done by the WHO Collaborating Centre for Influenza in London is ongoing but the H3N2 viruses that have been analysed remain antigenically similar to many of the viruses representative of those in circulation in the 2016/2017 season.

What is Japanese flu, and is it a strain that the UK has experienced before?

Japanese flu refers to influenza B viruses of the B/Yamagata lineage. The trivalent vaccine is not expected to afford good levels of protection against infection by this lineage of virus but there may well be some protection from the trivalent vaccine due to some level of protection across the influenza B lineages. Viruses of the B/Yamagata lineage last predominated among the influenza B viruses in the winter of 2014/2015. The most recently analysed viruses of the B/Yamagata lineage remain antigenically similar to the vaccine virus present in the quadrivalent vaccine.

Are these strains actually more severe than in normal winter outbreaks?

The winter months of 2014/2015, when influenza H3N2 was circulating, resulted in the largest number of excess deaths since the winter of 1999/2000 in England and Wales, and similar observations were made in Scotland and Northern Ireland. Most of the excess mortality was in the elderly (>75 years of age). The winter of 2016/2017 also showed a marked excess mortality. Many of these deaths will have been associated with influenza and in each of these years influenza A(H3N2) predominated. Nevertheless, H1N1 influenza can have a serious impact on health.

Is this year’s outbreak progressing like a normal season, or is there actually a big surge in cases compared to normal years?

The current rate of influenza in UK is considered to be ‘medium activity’ at present and higher than the rate seen at the same time in 2016/2017.

Is there any way to tell whether this outbreak could become an epidemic?

It is still too early to know whether the increasing trend of influenza activity will be sustained. The numbers of cases seen in the next two weeks are likely to be key to the overall impact influenza this winter.

What treatments are there for flu- are there any antivirals available?

There are antiviral medicines available and these can provide protection. Public Health England provide guidance for the use of antiviral medicines for influenza (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/648758/PHE_guidance_antivirals_influenza_201718_FINAL.pdf).

What strains of flu does the flu vaccine cover and what is the level of protection for this year?

In March 2017, the WHO recommended that influenza vaccines in use for the 2017/2018 influenza season (northern hemisphere winter) contain: an A/Michigan/45/2015 (H1N1)pdm09-like virus; an A/Hong Kong/4801/2014 (H3N2)-like virus; a B/Brisbane/60/2008-like virus and it was also recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Phuket/3073/2013-like virus. The recommendation was published in the Weekly Epidemiological Record Vol 92, 117-128.

The level of protection is assessed during and after each winter and these results are published. The most recent estimates from the UK were published in November 2017 and concluded for the 2016/2017 influenza season ‘Adjusted end-of-season vaccine effectiveness (aVE) estimates were 39.8% (95% confidence interval (CI): 23.1 to 52.8) against all influenza and 40.6% (95% CI: 19.0 to 56.3) in 18-64-year-olds, but no significant aVE in ≥ 65-year-olds. aVE was 65.8% (95% CI: 30.3 to 83.2) for 2-17-year-olds receiving quadrivalent live attenuated influenza vaccine’ Pebody et al., Euro Surveillance 2017 Nov;22(44). doi: 10.2807/1560-7917.ES.2017.22.44.17-00306. The 2016/2017 influenza season in England and Wales showed that H3N2 viruses predominated early followed by influenza B viruses of both the B/Yamagata lineage and the B/Victoria lineage detected at a ratio of ~3:1 .

Who is more vulnerable to flu, and who should get the flu vaccine?

Flu vaccination is available every year on the NHS to help protect adults and children at risk of flu and its complications. Vaccination is recommended for certain groups of people in which the disease might be more severe, these include anyone aged 65 and over, pregnant women, children and adults with an underlying health condition (such as long-term heart or respiratory disease), adults with a weakened immune system and those in long-stay residential care homes. The flu vaccine is routinely given on the NHS as an annual nasal spray to children in England and Wales aged 2 and 3 plus children in reception class and school years 1, 2, 3 and 4, and to children aged 2 to 17 years at a particular risk of influenza. In addition, frontline health and social care workers are offered flu vaccination.