A…surprising…article about influenza (flu) vaccination appeared in the Conversation today. The piece, entitled “The flu vaccine is being oversold – it’s not that effective“, tells us that we are being given medical advice about flu vaccination that isn’t consistent with 3 reviews of the literature which focus influenza vaccine effectiveness.
In reply to this article, Professor Allen Cheng spelt out some of the many issues around influenza vaccination. I think the response nicely highlights how complex the issues are. Those complexities are not captured by the Conversation piece. In fact, they very much undersell many important points.
I asked Professor Cheng if, as a VDU Guest Author, he would consider giving permission to post his response here. He agreed.
Professor Allen Cheng, Professor in Infectious Diseases Epidemiology, Monash University, is involved in national advisory committees for immunisation (ATAGI and ACV), but the views expressed below are his and do not necessarily reflect any Government or Organisation’s views.
I would hate to think that the take away message from this piece is that flu vaccine is useless. The national program, which provides free vaccine, aims to protect individuals who are at high risk (chronic illness, pregnant women, Indigenous Australians) from severe disease, and I’d urge readers to have this discussion with their GPs and specialists if they are in these groups.
Drilling into those numbers…
2% and 1% may sound like small numbers, but just to put that in perspective, that would be 200,000 infections in Australia, and obviously that figure varies from year to year. Interestingly, Prof Del Mar’s other review (on physical interventions) says “Approximately 10% to 15% of people worldwide contract influenza annually, with attack rates as high as 50% during major epidemics.” which seems at odds with the 1-2% figure quoted here.
If we took that approach for other vaccines, we wouldn’t use the cervical cancer vaccine as 164 of 165 women wouldn’t benefit. (https://cervical-cancer.canceraustralia.gov.au/statistics ) or meningococcal C as 39,999 of 40000 kids wouldn’t benefit (as the pre-vaccination rate was ~2.5 per 100,000)
In 2017, we detected over 4000 admissions with confirmed influenza at 17 hospitals (which would represent something like 30,000 admissions nationally), so reducing that figure would probably be cost effective solely from a hospital point of view, even before factoring in sick leave, GP costs etc.
Influenza testing: the tip of the iceberg…
It is also thought that PCR confirmation (at least in surveillance systems, less so in clinical trials) represents only the tip of an iceberg of illness – although this isn’t well understood, it is well described that non-flu illnesses such as heart attacks and pneumonia also go up in the flu season, and it is likely that flu vaccine protects against some of this. There are certainly many patients who get sick from flu and never go to a GP or hospital, and of those that do, many don’t get a test for a diagnosis, so the 233,000 flu notifications last year (ie 1% of the population) almost certainly is an underestimate of the true burden of disease.
It is also important to note that the clinical trials of flu vaccine have important limitations – they generally were performed in healthy adults although the authors mention the smaller number of studies in other groups. The sensitivity of influenza case definitions is different in other groups – the elderly have fever less commonly, and the rates of illness are higher in children. The national program aims to protect vulnerable people – pretty much everyone other than healthy adults – against severe complications from flu.
How effective are vaccine alternatives at interrupting virus transmission..?
I don’t think anyone is arguing against hand washing and masks in preventing transmission, but these are more complex and expensive interventions at a population level than a single vaccine dose and there’s no reason why we can’t vaccinate as well as improving hygiene.
Side effects from flu versus those from flu vaccination…
Finally, the authors point out that there are rare but serious side effects from flu vaccine, such as febrile convulsions in children and Guillain Barre syndrome (GBS). It is important to note that both of these complications also occur as a consequence of influenza infection. To put this in context, one study found that GBS occurred after 1 per million doses of vaccine, but in 1 in 60,000 influenza infections presenting to medical care. https://www.ncbi.nlm.nih.gov/pubmed/23810252 
One misconception that needs to be corrected is that seasonal vaccines have a role in preventing pandemics. Pandemics, such as that caused in 2009, are caused by a new influenza strain (H1N1 in 2009) that has not circulated previously. Therefore, these strains aren’t in the seasonal influenza vaccines, and pandemics need a new vaccine.