The importance of intellegence - certainly when it comes to influenza.

The complexity of understating the spread of influenza was again highlighted in a paper in Eurosurveillance recently.  In this paper the authors have looked at antibody levels and antibody quality to H3N2 and H1N1 influenza A viruses from pigs that have been known to spread to humans.   H and N; or haemagglutinin and neuraminidase to give them their full names, are two molecules found on the outside of the influenza virus, and it is changes in these molecules which mean that it is necessary to revaccinate against influenza each year.  They constantly change in a process called antigenic drift, and sometimes change suddenly in a process known as antigenic shift; the latter often occurring when an animal virus passes into and then spreads between humans. 

This is a particular problem with influenza because unusually humans share influenza viruses with a variety of animals with which we have frequent contact, namely birds and pigs.  A sudden antigenic shift, as occurred in 2009 with the introduction of a new H1N1 virus into the human population can spread because, being a new virus, there will be little immunity in humans.  The important thing to remember here is that it is not the jump into humans that is the problem (unless you are that human of course); but the subsequent transmission between humans.  That was the difference between avian influenza in 2005 and swine influenza in 2009, the former did not transmit widely between humans and the latter did.  Incidentally the latest virus to worry the world, H7N9 has made the first step, and there are tentative signs that it might have made the second, being transmitted between humans, but so far only a very small number of very close contacts.

Understanding the make-up of the H and N of viruses that are likely to circulate in the human population is important to ensure that vaccine can be made and that preparations can be put in place for health services.  However, it is a bit more complicated than just characterising the H and N numbers, since not all H1N1 for example are the same.

In this study the authors looked at antibody titres (levels) to different strains of influenza of pig origin, remembering that the last pandemic strain came from pigs.  When they looked at a variety of different H1N1 and H3N2 viruses what they found was that there were marked differences in antibody levels in different age groups to different viruses.  For example, those born between 1968 and 1999 had high levels to one type of H3N2, but very low levels to another more recent variety.  These differences reflect exposure to viruses over time, and have been seen before, for example older people tended to be less at risk of catching the last H1N1 pandemic virus because of existing immunity from previous exposure to a similar virus.

What we learn from this is that influenza should probably not be considered to be a single virus, but a large and ever changing family of viruses that can affect different groups in different ways.  The other thing that comes across is that immunity, like knowledge, is a life-long affair.  Just as we learn and collect knowledge, so we learn and collect immunity.  The key is to avoid damage while we are collecting it, which once again emphasises the importance of age and group-specific vaccination policies that reflect the ever-changing world of influenza.  If you want to know more about the UK situation, Public Health England is the place to look.  It is worth keeping an eye on this page, because the situation is constantly changing.

Hoschler (2013) Eurosurveillance 18, 36, 05 September 2013  

Influenza vaccination for children - Fluenz

Sorry - not even August and another influenza story but this is a big one.

It has been a busy few days in the world of childhood vaccination.  Fresh on the heels of advice from the Joint Committee on Vaccination and Immunisation (JCVI), the body that advise the Department of Health about vaccination policy not to introduce meningococcal type B vaccine yet, we now have details from the Department of Health about routine influenza vaccination for children over the age of 2 years.

Essentially it is to be offered to all children who are aged 2 and 3 years on the 1^st September; and to older children up to the age of 10 years in some pilot areas.  There are a number of things about this that need to be highlighted:

• Influenza is not always a mild illness, and it can lead to more serious infections.
• Vaccination has two effects, it protects the individual, but by reducing the risk of them catching the disease it also protects other people.  So if your child doesn’t get the flu then they can’t give it to siblings, grandparents…etc.  This is the same thing that I discussed previously with regards to taking time off work reducing the spread of influenza.  So even if you are not worried about your child, what about their grandparents and other contacts?  What about that child at nursery who has asthma?  I don’t want to lay it on too thick, but there are a lot of people around who can become very ill with the flu.
• This is not the same as the normal seasonal flu vaccine.  That is an inactivated vaccine (note inactivated – it can’t give you the flu!); this is a cold attenuated live vaccine.  This means that it is alive (as much as viruses can be described as ‘alive’) but has been altered so that it can only grow in cool environments – such as the nose, which is much cooler than the lungs and respiratory tract.  This also raises the interesting prospect of the altered strain circulating in the community, that people could ‘catch’ the vaccine virus and become immune that way (which would be a good thing!)
• It is not an injection but a squirt up the nose (two squirts actually, one up each nostril).
• If you or your child is in a risk group, this does not replace the need for annual vaccination, it is an additional layer of protection.  You (or your child) still need to be vaccinated as normal.
• Finally, immunity is not immediate; you need to give the system a good 2 weeks for immunity to develop.

 There are a few children who should not have it: those under 2 years, those with egg allergy, children who are severely immune suppressed and other children who live in their house, and children with asthma who are wheezy at the time of vaccination.

Although this is a new vaccine to the UK, the Americans have been using it for some time.  For people who are worried about it I would just say this, if you are not convinced of the need for your child to be protected; if you are not convinced by the part that this will play in reducing the spread of flu, and I respect (but disagree with both of these); it can’t be worse than catching the flu anyway – because that is all it is, but in a form that is much, much, much less likely to cause disease.

The advice from the JCVI is here; the guidance that healthcare professionals use (the 'Green Book') is here, always check before use as  it changes quite regularly; and the letter from the Department of Health is here.

It may be sunny but influenza will soon be here..

As the temperature reaches the low 30°Cs it may seem difficult to imagine, but influenza season will soon be upon us.  One of the many dilemmas of flu season is at what point one should go sick or keep a child at home.  A recent study from the United States has looked at this very subject, but from a public health perspective, what is the effect of someone with flu going to work on the wider community? (Kumar et al (2013) Am J Pub Health 103 1406-1411).

This was a study done using agent based modelling, in other words it was a computer simulation.  Probably the most important thing to do when you look at a model such as this is to check the assumptions made in the model, so for example here they had different scenarios: one where not everyone had access to paid sick leave; one where everyone did; and some where employees were able to take either 1 or 2 ‘flu days’ regardless of access to paid sick leave.  In all models it was assumed that 28% stoically went to work even if they had the flu; and that the R0 (the average number of infections caused by each infected person) was 1.4 – pretty typical of seasonal influenza.  However, in some circumstances, such as schools and nurseries it may be much, much higher.

The results of the modelling showed that the attack rate (the proportion of those without immunity who were exposed and caught the flu) was 11.54% in the mixed sick-leave scenario; 10.86% where paid sick leave was universal; only 8.62% where 1 flu day was allowed; and 7.01% where employees were able to take 2 flu days.  In a simulated population of 575 866, this equates to 66 444; 62 538, 49 611; and 40 386 infections respectively.  That is a lot of numbers, but what it is saying is that the 2 flu day scenario reduced the number of infections at work by 26 059 or 39% from the baseline mixed sick-leave scenario.

So the lesson from this is that it may be better for the economy for people to go off sick rather than go to work when they are ill.  Remember that once one has the flu, you can then infect other people who may be in one of the high risk categories for severe disease, so the impact is almost certainly even wider than this study suggests.  This can of course be mitigated by getting vaccinated - and the flu vaccine is gradually being rolled out to all children aged over 2-years (not this is not an injection!); and others in the high risk categories should already be getting it.  More details here (it is a bit wordy - but keep going - it is on page 10!).

 Now major warnings in interpreting these and similar data:

1. All models are wrong – the trick is to get the model that is least wrong
2. Look at the assumptions – do they seem sensible?
3. Does the model allow for ‘random behaviour’?  These are called stochastic models and while they are more lifelike, they are also much more complicated.  The opposite, where people essentially do as they are told or behave the same are called deterministic models.
4. In epidemiological studies always be clear about the case-definition; how do you know someone has the flu?  This is crucial, because we need to know that we are talking about influenza and not just a bad cold.  The UK case definition and other epidemiological data are here.

Finally reading this paper I learned a new term, which is ‘presenteeism’ – which is going to work or school when ill, something I may have been guilty of in the past...  More about flu to come, in the meantime enjoy the sun!