If you don’t swab for flu you won’t find it?
Okay, so I’m a cynic, you all know that by now. But are we not “seeing” flu because we’re not looking for flu? If this is the case we could probably convince ourselves that there isn’t any flu.
However, despite being swamped with Covid-19 I think most hospitals are still looking for flu. It is the same sample type and the same type of test. In fact you can take the exact same swab to look for Covid-19 and flu, and this is what most hospitals will be doing; as dual infection may make people a lot sicker and we don’t want outbreaks of Covid-19 PLUS flu in our wards.
Oddly there have been other suggestions that a number of other types of infections are also behaving a bit differently this year than expected. For example the number of sexually transmitted infections being diagnosed is down; is this because people aren’t having risky sex or is it because their infections aren’t being detected? Given that we’re apparently in the “Coronial” baby boom, I suspect due to STD clinics becoming “Covid-safe appointment only” they are less busy so these tests just aren’t being done. On the other hand we are currently seeing more foodborne infections such as campylobacteriosis and salmonellosis and the theory is that a lot of people who don’t normally cook or prepare food at home are now cooking or should I say “under-cooking”, so food poisoning is up! Who knows?!
However, I think labs ARE looking for flu, but it just isn’t there… so the next question is why not?
Infection control precautions for flu are the same as for Covid-19
Okay I’d like to think that as the infection control precautions for Influenza Virus are the same as for SARS CoV2 - this is the reason for no flu. A big pat-on-the-back to all those infection control teams (ICTs) out there, they can take the credit for controlling flu this year! But maybe it’s a bit more complicated than this?
If the Covid-19 infection control precautions (hands, space, face) were being implemented well in the community, then we would expect them to have an effect on Covid-19 numbers as well as flu. Although there has been no flu, we have seen huge numbers of cases of Covid-19 across the UK! So this would argue against infection control precautions preventing transmission of flu. Sorry ICTs!
However, maybe the precautions don’t need to be as good for flu as for Covid-19. Why would this be? Well SARS CoV2 is more transmissible than Influenza Virus. Now don’t get me started on “what do you mean more transmissible”… I mean the reproductive rate for SARS CoV2 is more than for Influenza Virus. SARS CoV2 has an R0 value of about 3, that is, each person with SARS CoV2 infects three other people, whereas Influenza Virus has an R0 of 1.3-1.5 which, because we can’t infect “half a person” (even those called Arthur! Ha ha!), in reality this means that two people with flu infect three other people.
So, if the R0 of an infection is less, then the infection control precautions to stop its transmission do not need to be quite as stringent as if for an infection with a higher R0. Think gloves and aprons for C. difficile versus hazmat suits for Ebola!
In this case maybe the precautions and restrictions in place across the UK to prevent transmission of SARS CoV2 are enough to completely prevent Influenza Virus (but seemingly not high enough for SARS CoV2)… maybe… or maybe everyone just had their flu vaccine this year?!
Vaccines can prevent flu
Every year there is a bit of a competition between hospitals to see who can vaccinate more staff against flu. Apart from a bit of friendly rivalry there is a serious reason for this; Influenza Virus kills people. Every winter there are thousands of excess deaths due to flu, and hospitals want to do the best they can to protect any vulnerable people admitted from catching flu from its staff!
This year as everyone was terrified of having a “bad flu year” on top of Covid-19, the flu vaccine uptake must have been really high, right? Well no, not really. Across the South East the general uptake is about 75% in the over 65-year olds, 45-50% in children and only 70% in healthcare workers. To my mind this is about the same as any other year and a bit disappointing really, I thought it would be higher.
As we have blogged before, the flu vaccine is based on estimates (read guesses!) of what is likely to be the next variant of Influenza Virus to hit the Northern hemisphere. It is often a partial match and so the vaccine is only partially successful; but enough to protect lots of people. However, we would still expect to (and do) see a lot of cases of flu each year.
So given the average flu vaccine uptake and the vaccine’s average efficacy, we would still expect to be seeing cases of flu, but we are not, so where has all the flu gone?
Flu is subject to travel bans
We often refer to flu as “seasonal influenza” because it only really appears in the season of winter. Winter is a great time for transmitting respiratory viruses in case you hadn’t noticed (!) because we all cram inside our houses to avoid the lousy weather, we turn the central heating on for warmth and the humidity drops making droplet transmission more effective. And this is all very important regarding transmission (yes, yes, yawn, bore) but if there is no flu here our winter hibernation routine wouldn’t matter; if there is no flu, flu can’t be transmitted.
Rather than being seasonal, flu is actually better thought of as being “migratory”. In some respects Influenza Virus is a bit like a “confused bird” which flies South for the summer then comes back in the winter. We give our flu to the Southern hemisphere in our summer before getting their slightly modified flu back when winter arrives.
Now Influenza Virus can’t “fly” or transmit that far, normally a couple of metres at best, but it can be “carried”, especially “in” people. Remember a virus needs a host to reproduce and survive and so the main route of transmission of most human respiratory viruses is from person-to-person. But, if people are not moving, and especially people aren’t moving from the Southern hemisphere to the Northern hemisphere, the amount of Influenza Virus being spread will be very, very low. For most of last year there have been severe travel restrictions between Australia, New Zealand, South America and Africa to Northern countries, and therefore very few opportunities for the spread of infections (the travel bans were ironically a bit late for Covid-19… but I digress).
I suspect that Influenza Virus is still present in countries around the World but at very low numbers due to a combination of no new flu introduced from abroad, natural post summer reduction and herd immunity from the previous flu season. The herd immunity will be pretty effective as there won’t be many non-immune hosts for the virus to infect and mutate within in order to spread further; remember Influenza Virus undergoes a process known as “antigenic drift” all the time whereby it’s genetics change slightly during a season in order to start another “season” later in people whose immunity is no longer as effective to this now slightly changed virus. It’s a sneaky virus huh?!
So, Influenza Virus may just still be on its summer holidays and may not come back until after all the travel restrictions for Covid-19 have been lifted. Let’s just hope it isn’t too changed after its trip otherwise we may follow the Covid-19 pandemic with an influenza pandemic… now there’s a cheery thought…! (ARGH!)
So, whatever the reason - there is no flu around at the moment. To be fair it’s probably because of elements of ALL the things I’ve talked about:
- Not doing as many tests for Influenza Virus as normal
- Infection control precautions for flu are already ramped up because of Covid-19
- There has been a push to vaccinate against Influenza Virus
- There is less opportunity for Influenza Virus to be introduced from the Southern hemisphere
What the proportion of each aspect is I suspect we’ll never know, but for now I don’t really care, not having a bad flu season on top of Covid-19 is great and I’m not going to complain! Well not about that… Maybe about all those “booking a jab and go summer holiday” when NHS staff have had all their leave cancelled or “forced” to be carried over or just “lost”… mutter, mutter! “Jab and Go!”... Really, please “Jab and stay put… and stay safe!”!!!