Waning Influenza Vaccine effectiveness

Will the influenza vaccine protection really run out before the end of the season?

Short answer – we don’t really know. The optimal TIMING for influenza vaccination is not clear.

However, there is clear evidence that the influenza vaccine stops people getting seriously sick and even dying from influenza. This is especially true for persons over 65 years of age (seniors), and those with other medical problems.

Its all about Timing

Recently there have been reports in the media reporting waning influenza vaccine effectiveness and suggesting it is even dangerous to have the influenza vaccine “too early”. or “…The Australian Medical Association is urging people to hold off getting this year’s flu vaccine…”

I have been told a recent story of an elderly unwell patient presenting for their flu vaccine. He was told by the GP to “come back in June, as to have it now is a waste of time”.

What does the data say?

In my view, the data on the waning effectiveness of the influenza vaccine toward the end of the season is still shaky.  Delaying influenza vaccination may not be a good idea.

My reading of the scientific literature is that more research is needed. The data suggests that in some previous influenza years, and for some strains of influenza (particularly H3N2 strains), and for some groups eg seniors, the protection from influenza may decrease the longer it is from the date the influenza vaccine was given.

The significance of this waning influenza vaccine effectiveness, if and when it does occur, is also uncertain. This editorial said “Vaccination appeared to remain efficacious throughout an influenza season, despite a modest decrease in the inactivated influenza vaccine’s efficacy over time”.

There are many variables. Scientists have to use observational studies for this research. These studies are not as accurate as the gold standard double blind placebo controlled trials. Some variables may be hard to statistically account for. [Issues like the interaction between herd immunity and spread of the virus, the mutation of the virus as the season progresses, the difficulty of making a vaccine that exactly matches the current strain (let alone what the virus mutates into), an individuals’ medical history and ability to make antibodies, their amount of exposure to the flu virus or the flu vaccine, this year or in previous years – to name a few.]

Waning influenza vaccine effectiveness is a bit academic at the moment. There is no government free influenza vaccine available yet anyway (2.4.18). Furthermore, there are two new  ‘turbocharged” vaccines that the seniors will –  in due course – be offered free.

These newer vaccines are supposedly better at helping seniors make antibodies. Unfortunately, there is no data yet which of the two ‘turbocharged’ vaccines is the better of the two, or even which one wanes or does not.

Frankly, it is also a bit late in the season to be saying  “hold on – don’t have the vaccine yet”. All the systems are in place to get people vaccinated. Much of the ‘waning data’ is a few years old.

Problems with delaying influenza vaccination

As I see it, the problems with delaying the influenza vaccine are:

• We do not know if this apparent waning is significant for all flu vaccines, people or circumstance.
• We do not know if this degree of waning is enough to balance the risk of exposing unvaccinated persons to the risk of full-blown influenza.   How significant really is this waning influenza vaccine effectiveness?
• We do not know exactly when the 2018 influenza virus will arrive and peak. It may come early, especially if no-one is vaccinated until later in the season.
• We do not know which strains are coming, and what mutations will occur during the season.
• This kind of last minute, negative communication may decrease confidence in vaccination, mean lost opportunities to vaccinate, and might even somehow give fodder to the anti-vaccine lobby.
• Patients may be sent away and not come back. Not having a flu vaccine will definitely mean a greater risk than any potential waning influenza vaccine effectiveness late in the season.

AND from my perspective (running a travel medicine clinic), travellers are going overseas now. So they need the vaccine now; Influenza is the number one vaccine-preventable disease of travellers.)

In Summary

It is better to have the influenza vaccine than not, especially if you are over 65 years or have medical problems. It might be marginally better to have the influenza vaccine later in the season, but it’s a bit of a gamble – if the flu hits early, you lose BigTime.

References

Waning Influenza Vaccine References