Medical Matters: Significant threat to at-risk groups from new variant of flu

To paraphrase the Eagles song, there’s a new (influenza) bug in town. It’s nothing on the scale of a swine or avian flu, but sufficiently unusual to suggest we face a different experience from the usual seasonal flu outbreak.

The predominant virus circulating in the Northern hemisphere this winter is Influenza A (H3N2). In composing the three-strand flu shot for the 2014/2015 season, the World Health Organisation (WHO) included a H3N2 variant, but not of the exact genetic make-up of the influenza A that is circulating around Europe at present.

For WHO, the decision – which it has to make many months in advance – is an informed guess. Most of the time, the experts get it right. However, this year they plumped for Influenza A/Texas/50/2012 (H3N2)-like strain in the vaccine; what emerged in circulation is influenza A/Hong Kong/5738/2014 (H3N2)-like, a group of viruses that show antigenic drift from the vaccine strain.

Danger to at-risk groups

What does this mean for us? Most of the people in the at-risk groups who diligently received their flu vaccination before Christmas will not have sufficient antibodies of the right type in their system if H3N2 comes calling. Their best hope is that the vaccine will mean the severity of the infection will be somewhat ameliorated, and it may help them avoid hospitalisation. But with an estimated overall effectiveness of just 6 per cent, this year’s vaccine is clearly not matched to the H3N2 bug it is designed to ward off. An indication of the reduction in the effectiveness of the vaccine may be the recent excess mortality reported among older people in six European countries.

A characteristic of this year’s predominant strain is that it is targeting older people. The main outbreaks have been in nursing homes. Hospitals have also been affected, with at least four major teaching hospitals closing their doors to visitors for varying periods. So far, reports of the virus in the community are relatively muted. Yes, the influenza-like illness (ILI) activity level is raised above baseline, but at 36.8 per 100,000 population in Week 6 it is stable and nowhere near epidemic proportions.

Might we escape the worst of the flu this winter? Signals from the rest of Europe are not encouraging. According to the latest figures from the European Centre for Disease Control (ECDC), flu activity is high in Poland, Denmark and the UK. Given the level of interconnectivity between Britain and Ireland, we may yet see the impact of elevated flu levels from across the Irish Sea. In addition, the flu season was late this year, so it is likely we have not experienced peak influenza activity just yet. And the proportion of influenza-related calls to GP out-of-hours services here increased significantly during week 6, to 4.9 per cent, Health Protection Surveillance Centre (HPSC) figures show.

Because of the low effectiveness of the annual flu vaccine, doctors and patients must be ready to make more use of anti-viral medication than might normally be our practise. Two antiviral drugs are licensed for use in the Republic: oseltamivir (Tamiflu) and zanamivir (Relenza). It has been shown that early antiviral treatment can reduce the risk of some complications from influenza: middle-ear infection in young children, and pneumonia and respiratory failure among adults. The drugs have also been shown to shorten the duration of flu and to reduce hospitalisation and mortality among patients with severe infection.

Complicated influenza

While those with a complicated influenza will almost certainly be given either Tamiflu tablets or a Relenza inhaler, someone with no underlying disease who develops classic flu symptoms – the rapid onset of fever, cough, sore throat, runny nose as well as severe headache, muscle aches and overwhelming tiredness – will also benefit. One of the keys to successful treatment is to start the anti-virals within 48 hours of the first symptoms appearing.

If you are struck down by flu, I hope your return to “life in the fast lane” is speedy.

mhouston@irishtimes.com | muirishouston.com