Vaccine for the New Swine Flu?

27 04 2009

No one knows if this small outbreak of swine influenza A (H1N1) is going to explode into a major pandemic, or be a paragraph in history books.

The world is prepared to combat such a pandemic.  Local, state and national government health agencies around the globe have all been working together to put plans in place.  If this turns into something big, everyone has a role to play and they’re ready to take action steps.  One action step may be the development of a vaccine.

Discussions are taking place at the CDC and elsewhere to determine if a vaccine should be developed for the new flu strain.  Although it appears so, it’s not the no-brainer choice.  If vaccine manufacturers stop developing their usual fall flu vaccine and shift to making a vaccine for the swine strain, then what happens next September, when flu season starts and we have no seasonal flu vaccine?  Or, should the vaccine for the new strain be incorporated into next season’s regular flu vaccine?  Will that work?  Not likely, and if it did, would it delay both vaccines too much?  Who absorbs the extra cost if this outbreak takes a break or goes away completely?

Lots of questions that must soon be answered.

The CDC is developing a seed stock of the new swine flu strain as a first step.  This stock will allow for vaccine production, should that be the course taken. 

There are a couple of ways to develop seed stock – the slower way is by reassortment, which is where scientists inject two different flu strains into fertilized chicken eggs – one is a strain that does not cause disease (and it grows well in eggs) and the other is the flu strain that is causing disease, in this case swine influenza A (H1N1).

The two different flu strains multiply and their genes mix with one another in the eggs.

After the multiplying and mixing, all the strains of flu virus present in the eggs are then screened to find the one that has the right combination of genes, some from the non-disease-causing virus that allow the growth in eggs and others from the disease-causing virus to stimulate the immune response.  This “seed” virus is then injected into millions of eggs for production of the new vaccine.

The other way to develop seed stock is by reverse genetics.  This is somewhat new and has not yet replaced reassortment as the go-to method of developing seed stock.

Using reverse genetics, scientists splice some genes from a non-disease-causing flu virus with others from the disease-causing virus into little round pieces of DNA.  These little DNA pieces are called plasmids and they’re inserted into animal cells in culture to allow growth of the vaccine seed virus. 

The seed stock can then be grown in huge quantities either in cell cultures or chicken eggs.  This can happen much more quickly than using the reassortment method. 

No matter the method of generating seed stock, it will take months to end up with a vaccine for swine influenza A (H1N1).  We don’t even know if we’ll need it, but if we do – hurry up!



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