Influenza 2009 H1N1

Like most people I’ve been keeping an eye on developments.

My main sources are:  An excellent blog on the basic molecular biology of viral infections. And for the epidemiology : Effect measure
So much has already been published about swine-flu that I shall concentrate on just three aspects, virulence, vaccine production, complications.
First the good news. Virulence. Early on it was discovered that this H1N1 strain lacked a crucial marker for virulence  the production of a protein called PB1-F2. As far as I can tell this marker is still absent as the pandemic has developed. Also the virus does not appear to be changing much
“Another surprise from the sequence data is that the virus seems unusually stable in terms ofgenome evolution” …….. But, if this lack of viral evolution remains during the pandemic, then there is apparently little selection pressure on the H1N1 virus to change. This may be related to the limited preexisting immunity. People are infected by this virus, and before the host can mount an appropriate immune response, the virus has propagated sufficiently to reach high enough viral loads to facilitate transmission and spreading in the population.”
So far so good. We have a highly contagious but mild Influenza virus out there.
Next, the bad news. Vaccine production may face problems.
“Swine flu vaccine production has hit a snag, with manufacturers reporting a disappointingly low yield when vaccines viruses are grown in eggs.
The World Health Organization says so far the yield for egg-based production is half or less what manufacturers get when they make vaccine to protect against seasonal H1N1 viruses. The lion’s share of influenza vaccine is made by companies that grow the viruses in eggs.
New seed strains are being made in the hopes of increasing the vaccine yield, a report by the WHO’s vaccine chief, Dr. Marie-Paule Kieny says. But if the yield cannot be increased, it will slow the rate at which pandemic vaccine comes out of the production pipeline, adding to the time it takes to protect populations”
Helen Branswell Canadian Press July 12
and double checking on this article I came across the transcript of the WHO press briefing of July 13 which gives more detail on the problem so far:
“Dr Marie-Paule Kieny: First, in terms of yields, maybe there is some confusion between the reality that is in the slides, that is now recognized by the manufacturers and the regulatory authorities and the WHO Network that we have a strain which are currently available to make inactivated vaccine, the manufacturers only get moderately affected yields. This is not to say that the viruses grow poorly, it is that for a reason or another the hemagglutinin they can produce is either not stable or very low. It is not known what is exactly happening but in terms of output that they have of hemagglutinin at the end when they grow a virus, they have poor yields, poor as between 25 and 50 percent of the normal yields that they have with good yielders. What is the reason for this is difficult to know, that it is well known that some strains are good yielders and some are bad yielders, it happens that for the first series of strains which were generated and unfortunately, we did not come up with a good yielder. So that in order to remedy to that the WHO laboratory network is again trying to generate new vaccines viruses from wild type virus isolated from patients, and these will be tested again by the manufacturers and we hope that at least one of them or more than that we hope will be giving higher yields that would be comparable to the ones obtained with seasonal vaccines.”
Hopefully there will be enough vaccine for the Northern Hemisphere in time for the coming flu season but this problem is one to keep an eye on.
Next, if you’re an asthmatic or in any of the other “at risk” groups -and you don’t want to rely on being vaccinated in time and not getting flu in the first place- there is something you should be asking your doctor about: Vaccination now, not against Flu, but against secondary bacterial pneumonia as a complication of Influenza.
“Combined viral-bacterial pneumonia is common. In secondary bacterial pneumonia, the patient appears to be recovering from uncomplicated influenza but then develops shaking chills, pleuritic chest pain, and coughs up bloody or purulent sputum. Often influenza virus can no longer be isolated from such cases. The most common bacteria causing influenza associated pneumonia are Streptococcus pneumoniae, Staphylococcus aureus, and Hemophilus influenzae.”
Luckily there has been for some time a vaccine that protects against this. In the USA the CDC has issued:
that recommends vaccination for, amongst other at risk groups, “Adults 19-64 with Asthma”.
The NHS in the UK has I believe similiar guidelines in place.
Last, but very much not least, check that young children under 5 have received their pneumococcal vaccinations – they should have done as part of standard paediatric childcare in the UK and USA.


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