Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: Lawk on 26/09/2018 19:11:15

Title: How does flu immunity produced by the flu vaccine change over time?
Post by: Lawk on 26/09/2018 19:11:15

I was talking to a friend who claims he will get the flu shot in November and not like me now (September) as the protection only lasts 6 months.

I disagreed claiming that, while it is true that there might be new influenza strains during the season, the protection against those strains included in the vaccination should go beyond the season? Or am I wrong.

I thought that it only lasts for one season, because next season just inlcudes the new influenza viruses, or those thought to be in the season.

I guess my question is, hypothetical case: the vaccination fits the strain of influenza perfectly, and offers protection. Does it still expire after only 6 months?

I understand it is of no use if the prediction was wrong, or there was a mutation and the vaccination is not effective, but I believed that it should have longer protection for the ones included.
Title: Re: How does flu immunity produced by the flu vaccine change over time?
Post by: chris on 27/09/2018 09:30:09
Great questions; thanks for asking them and welcome to the forum @Lawk

With the exception of the live attenuated flu vaccines that are being used mainly in children, the majority of the influenza vaccines administered annually contain killed / inactivated flu viruses.

The bulk of these are made by selecting appropriate circulating human flu strains and using fertilised chicken eggs to grow large amounts of virus, which is harvested, purified and then chemically brutalised to destroy the infectivity while preserving the antigenicity. These are then mixed with an immune-stimulating adjuvant and administered as an intra-muscular injection ahead of each flu season, starting from about now.

In plain English, this process renders the vaccine strains of the viruses incapable of infecting you or growing but nevertheless preserves their chemical appearance. In this way they educate the immune system to recognise those strains of flu, should they be encountered for real.

However, what I think your friend is getting at is that the immune response stimulated by a killed vaccine is chiefly one dominated by the production of antibodies, which are sticky molecules capable of binding tightly to - and neutralising - foreign molecular structures like virus particles.

Antibodies have a limited lifetime in circulation, and although the cells that make them retain a "memory" of how to make that antibody, over time post-vaccination the levels of antibody in the blood, and the population of antibody-producing cells, dwindles, reducing the level of protection; if this falls below the threshold to attenuate infection, a person becomes susceptible to infection again. This tends to happen over a series of years post vaccination.

The other thing that happens is that flu viruses mutate continuously owing to errors introduced when the viral genetic material is copied. This is call "drift" and has the effect of endowing the flu with a virological face-lift that makes it much harder for the existing suite of antibodies to recognise in future. It's this drift that vaccine designers seek to surmount by updating the vaccine to include viral strains capable of provoking an immune response that will still neutralise these newcomers.

This all said, I don't believe there will be a clinically significant different between the level of protection conferred by a September versus a November vaccine administration. In fact, one could argue that if you wait for November, you may be more at risk because you could encounter and contract circulating flu in the interim while you are waiting for the vaccine, since flu usually begins to spread from October.

This podcast on the flu ( that we made this week may be helpful for you. It includes many of the details that I have discussed above.
Title: Re: How does flu immunity produced by the flu vaccine change over time?
Post by: Lawk on 27/09/2018 12:04:02
Thank you very much for the detailed answer!