Robert asked me why there are three different types of flu vaccine available this year. I didn’t know there were — I just received the standard shot from my GP due to asthma, much as I have in other years — so I had to look it up. First of all, what types of vaccine are there for flu?
- A live quadrivalent vaccine in the form of a nasal spray, offered to children between two and seventeen years of age
- A quadrivalent injected vaccine given to vulnerable adults between seventeen and sixty-five years of age, and to babies below the age of two
- An adjuvanted trivalent vaccine given to those over sixty-five years of age
(Quadrivalent and trivalent refer to the number of flu strains each vaccine protects against.)
The decisions as to which vaccine to use for each group are based on efficacy and vulnerability. A live vaccine actually contains infectious agents, although they are weakened so that they can’t cause serious infections. This usually produces the most robust possible immune response, since your body genuinely has to mount a defence, without causing undue danger. However, it can cause some symptoms of flu, which is why it isn’t given to vulnerable adults.
Vulnerable adults therefore receive a vaccine in which the infectious agents are no longer capable of causing active infection — ‘dead’ viruses, although viruses aren’t strictly speaking alive. This means they won’t be infectious, and they shouldn’t suffer actual flu symptoms. This is safest for people — like me! — who have respiratory problems already, for example. If I actually got sick with influenza, I would be more at risk of complications like pneumonia than the general population. The same is true of babies under the age of two, in whom the live vaccine isn’t licensed due to the level of side effects observed.
Finally, adults over the age of sixty-five receive a shot which contains immune-response boosting agents as well as the inactive virus. The elderly typically have lower immune function than younger adults, so this boost helps them mount an effective response in order to provide the best possible protection. Tests have shown that the adjuvanted vaccine is much more effective (on average, of course!) in this age group.
I suspect use of the live quadrivalent vaccine is going to spread, as it offers the best protection and is easy to administer, even in those who are afraid of needles! I suspect that healthy adults who elect to get a flu vaccine will ultimately be given the live vaccine for that reason. In any case, the guidelines at the moment are designed to provide the most effective possible vaccine within the bounds of safety. They’ll probably be expanded to provide the live vaccine to more people, as the safety and efficacy of the vaccine is tested in more and more of the population.