The Yorkshire Mouth
Sunday, 31 August 2025
Sunday, 23 June 2024
The Climate of Skiathos – Month-by-Month
Being a regular user of
various Skiathos-related social media groups and platforms, it’s common to see
questions asking what the weather is like on the island at a particular time of
year. If you’re reading this, it’s almost
certainly because you’ve asked such a question, and have been directed here.
It's important to be clear
that no one can guarantee what the weather will be like on Skiathos in advance,
but it’s equally true that you can be given a good idea what it will be like,
along with some idea of the possibility that it might be different to the
average.
The following information is
in month order, so just scroll down to the month you’re visiting, and read
on. Please note, if you’re going at the
very start, or very end of a month, it’s not a bad idea to read up on what the
weather is like in the adjacent month, too.
All
figures are averages based on
the 30-year period 1991-2020
Skiathos in January,
February, and March
Cool/mild, rather than
cold. The average minimum temperature in
January and February is 8°C, rising to 10°C in
March, the average maximum is 12°C, rising to 14°C in March with the mean average
temperatures being January and February 10°C, March 12.5°C. Those are the averages – the warmest days of
each month can regularly be 18°C in January, 19°C in February, and 22°C in March. The warmest temperatures recorded in the
30-year period were January 22°C, February 22°C, and March an eye-opening 31°C.
The coldest nights are usually around 2-4°C, though
it can occasionally be as low as -2°C in January. Sea temperatures are almost always below
15°C, so too cold for swimming.
Rainfall averages are 80mm
in January distributed over an average of 10 days, 70mm in February over 9
days, and 60mm in March over 8 days.
Sunshine hours averages are 3.5 hours per day in January, 5 hours in
February, and 6.5 hours in March. On
average, it’s sunny for 37% of daylight hours in January, 48% in February, and
54% in March. It
has been known to snow, and snow quite heavily in January, though most
years it doesn’t. If you visit for a
fortnight, you’re almost certain to see some rain, and there’s a reasonable
chance the rain could last for a significant portion of your visit.
IN GENERAL -
You can visit Skiathos at this time of year, but it won’t be for the weather or
the swimming.
Skiathos in April
Very mild.
The average minimum
temperature in April is 13°C, the average maximum is 17°C, with the mean average
being 15°C. Those are the averages – the
warmest day of the month can regularly be 23°C, whilst the warmest recorded in
the 30-year period was 26°C. The coldest nights are usually around 7.5°C,
though it can occasionally be as low as 5°C, so you’ll definitely need a jumper
and/or coat in the evenings. Sea
temperatures are almost always below 15°C, so it’s still too cold for swimming.
The rainfall average for
April is 40mm distributed over 7 days.
The sunshine hours average is 8.5 hours per day.
On average, it’s sunny for 65% of
daylight hours.
IN GENERAL -
April’s climate is a small, but steady improvement over the first 3 months of
the year, but whilst the odd day may feel like summer, you’re far more likely
to experience weather which feels very much like spring.
Skiathos in May
The tourist season for Brits
starts in May. That is to say, the first
direct flight to Skiathos from a UK airport, and the first package holidays
available from the big travel companies usually depart on or close to 1st
May.
Warm.
NOTE – There is usually a
fairly large difference between temperatures at the start of May when compared with
the end of the month. The average
minimum temperature in May is 18°C, the average maximum is 22°C, with the mean average
being 20°C. Those are the averages – the
warmest day of the month can regularly be 28°C, whilst the warmest recorded in
the 30-year period was 31°C. The coldest nights are usually around 12°C, though
it can occasionally be as low as 9°C, so a jumper or even coat for the evenings
is advised. Sea temperatures are usually
around 18°C, so still too cold for swimming for most, though doable for the
more hardy souls, particularly towards the end of the month.
The rainfall average for May
is 40mm distributed over 6 days, so not much better than April. The sunshine hours average is 9.5 hours per
day. On average, it’s sunny for 68% of
daylight hours.
IN GENERAL – May
sees a significant step up in temperature over April, but otherwise the average
climate across the month is another small, but steady improvement over the
previous month, and starting to feel like summer. May is certainly a time where it’s relatively
important to consider whether you’re going towards the start or end of the
month, as the averages improve fairly rapidly.
Having said that, you’ll be fairly unluck to have a fully ‘bad week’,
and extremely unlucky indeed to have a ‘bad fortnight’ if you go for the first
two weeks in May, whilst a visit during the second half of the month won’t be
too much different to June. The end of May
is a far safer bet.
Skiathos in June
Warm-to hot.
The average minimum
temperature in June is 22°C, the average maximum is 27°C, with the mean average
being 24.5°C. Those are the averages –
the warmest day of the month can regularly be 28°C, whilst the warmest recorded
in the period was 40°C. The coldest nights are usually around 17°C, though it
can occasionally be as low as 14°C, so it’s best to consider taking a light
jumper for the evenings, just in case, though you’ll get less use out of it the
later in the month you get. Sea
temperatures are usually around 22°C, so quite cool for swimming, though most
will find it bearable, particularly towards the end of the month.
The rainfall average for
June is 25mm distributed over 4 days, so a big improvement over May. Sunshine hours average 11 hours per day. On average, it’s sunny for 73% of daylight
hours. Occasionally you’ll see steady
rain in June, but more often it’s a quick, heavy thunderstorm.
IN GENERAL -
June sees a significant step up in average temperatures across the month over
May, but is otherwise just another small, but steady improvement over the
previous month. It’s drier, and there’s
steady improvement in other areas; it’s now unambiguously summer. There’s not a significant improvement between
June and July, so this is the last time of the season when the part of the
month you go shows any considerable improvement. Like May, June is a time where it’s
relatively important to consider whether you’re going towards the start or end
of the month, as the averages improve fairly rapidly. The weather at the end of June should be very
similar to July and August.
Skiathos in July &
August
There’s not a lot of
difference between July and August, with the climate being warm-to hot.
The average minimum
temperature in July-August is 24°C, the average maximum is 29°C, with the mean average
being just over 26.5°C. Those are the
averages – the warmest day of the months can regularly be 33.5°C, whilst the
warmest recorded in the 30-year period were 43°C in July and 38°C in August.
The coldest nights are usually around 20°C, though it can occasionally be as
low as 16-17°C, so a jumper shouldn’t be necessary for the evenings, unless you
feel the cold very easily. Sea
temperatures are usually around 25°C, which is the warmest of the year, and
good for swimming.
The rainfall average for
both July and August is 20-25mm distributed over 2 days per month, so similar
to June. Sunshine hours average is
around 12 hours per day. On average,
it’s sunny for around 83% of daylight hours in both months. The rain, if and when it comes, is usually in
the form of very quick, dramatic thunderstorms.
You’ll almost certainly not have a whole day washed out.
IN GENERAL -
July and August’s climate is a small step up over June’s average, with only sea
temperatures being a significant difference.
This is peak summer. There’s not
a significant improvement between late June and July/August, and whilst some
figures take a turn for the worse in September, that’s mainly caused by a dip
towards the end of that month. In short,
the climate on Skiathos is very similar from 1st July through to 31st
August.
Skiathos in September
The climate changes during
September, being unapologetically summer at the beginning of the month, but nudging
towards autumnal as you near the end.
The average minimum
temperature in September is 21°C, the average maximum is 26°C, with the mean average
being 23°C. Those are the averages – the
warmest day of the month can regularly be just over 30°C, whilst the warmest
recorded in the 30-year period was 36°C. The coldest nights are usually around
15°C, though it can occasionally be as low as 12°C; a light jumper is advised
for evenings, especially towards the end of the month. Sea temperatures hold up well, usually being
around 24°C, which is still good for swimming, and not far behind July-August.
The rainfall average for
September is 40mm distributed over 5 days per month. Sunshine hours average is around 9.5 hours
per day. On average, it’s sunny for 76%
of daylight hours. It can rain for
extended periods, but whilst you may possibly see most of a week cloudy and
rainy towards the end of the month, that’s relatively unusual. Nonetheless, twice in recent years there’s been heavy flooding, caused by heavy rain over half a week, or so. Both times in mid-September.
IN GENERAL -
September’s climate is a step down from July and August, with only sea
temperatures holding up. Importantly,
this deterioration occurs during the month, so whether you’re going during the
first or last week or fortnight makes some difference. Having said that, you’ll be fairly unluck to
have a fully ‘bad week’, and extremely unlucky indeed to have a ‘bad fortnight’
if you go for the last two weeks in September, whilst a visit during the first
half of the month probably won’t be too much different to July/August.
Skiathos in October
The tourist season for Brits
ends after the first week of October.
That is to say, the last direct flight to a UK airport from Skiathos,
and the last package holidays available from the big travel companies usually ends
on or close to 7th October.
The climate changes during
October, from hanging on to summer at the start of the month, to being
unapologetically autumnal towards the end.
The average minimum
temperature in October is 17°C, the average maximum is 21°C, with the mean average
19°C. Those are the averages – the
warmest day of the month can regularly be 27°C, whilst the warmest recorded in
the 30-year period was 31°C. The coldest nights are usually around 12°C, though
it can occasionally be as low as 7°C; a light jumper or coat is advised for
evenings, especially towards the end of the month. Sea temperatures continue to hold up well,
usually being around 21°C, which is still just about fine for swimming,
especially at the start of the month.
The rainfall average for
October is 70mm distributed over 7 days per month. Sunshine hours average is around 7.5 hours
per day. On average, it’s sunny for 68%
of daylight hours. As with late
September, it can rain for extended periods, but whilst you may possibly see
most of a week cloudy and rainy, that’s relatively unusual.
IN GENERAL -
October’s climate is another step down from September, with only sea
temperatures holding up. And once again,
this deterioration occurs during the month, so whether you’re going during the
first or last week makes quite a difference.
Having said that, and given that the tourist season for Brits only
covers the first week of the month, you’ll be fairly unluck to have a fully
‘bad week’, and extremely unlucky indeed to have a ‘bad fortnight’ if you go
for the last week in September/first week in October.
Skiathos in November and
December
The climate changes from
autumnal to ‘mild-winter’ over these two months.
The average minimum
temperatures are 13°C in November and 9°C in December, the average maximums are
17°C in November and 13°C in December, with the mean
averages being 15.3°C in November and 11°C in December. Those are averages – the warmest day of the
month can regularly be 23°C in November and 19°C in December, whilst the
warmest recorded in the period was 27°C in November and 23°C in December. The
coldest nights are usually around 8°C in November and 3°C in December, though
it can occasionally be as low as 4°C in November and just 1°C in December; a
‘big coat’ is mandatory. Sea
temperatures hold up fairly well in November at 18.5°C, which would be doable
for some were it not for the cold air once you left the water. In December this falls further to 15.5°C,
which is a non-starter for most. It has
been known to snow, and snow quite heavily in December.
The rainfall average for
November is 65mm distributed over 10 days per month, and 95mm over 12 days in
December. Sunshine hours average is
around 5.5 hours per day in November and 3.5 in December. On average, it’s sunny for 55% of daylight
hours in November, but just 37% in December.
If you visit for a fortnight, you’re almost
certain to see some rain, and there’s a reasonable chance the rain could last
for a significant portion of your visit.
Monday, 8 April 2024
I Tried DEET and I Still Got Bitten
Okay, that definitely happens. What went wrong? What are the possibilities? And perhaps most importantly, based on my
answer, what should I do next time?
Here are some possible reasons why you’ve been wearing DEET
all holiday, but still got bitten.
For fun, try to rank them in order of likelihood.
1. I didn’t apply it correctly. Let's face it, that's certainly not
impossible. If you’re away for 14 nights
and apply DEET 2 or 3 times a day, that’s a lot of applications you need to
make sure you’ve performed perfectly.
Putting anything else on, do you ever ‘miss bits’? Ever become distracted halfway through
applying, and forgot which limb(s) you’ve already done? So, might I have
missed a bit? You don't have to miss
a bit every time. Just once.
2. It got washed off. Did I say 2 or 3 times a day? If you regularly go swimming, you might
easily up that to 5 or 6. Or more. And remember, for each application, you need
to be as accurate and thorough as all the rest. So, might it have got washed off? You don't have to wash it off and not reapply
correctly every time. Just once.
3. I forgot.
We’ve all done it. Things we do
regularly, day-in, day out, which you might think you'd never forget, but you
just occasionally forget. I’ve left my
keys on my desk. I’ve left my phone at
home. I didn’t take my medication this morning.
Did I leave the iron on? Did I
put the bins out? Did I turn the
straighteners off? Did I lock the front
door? Let’s face it, we forget
things. We’re human. So, might I have forgotten? You don't have forget every time. Just once.
4. I was bitten in-between applications. True story.
In Florence recently I wore full length jeans and shirts (it was autumn)
and I got one single, solitary bite. It was
on my left leg, near the top, over to one side, just underneath my front-left
jeans pocket, that's the pocket where I always carry my wallet. The mosquito would have had to bite through
my jeans and wallet. I wore DEET all the
time, we had a plug-in in the room, so the only time I was unprotected was when
I’d had a shower and went out on to the balcony to re-apply. AH! So
there was a time, a small window of opportunity, where I had no DEET on, and
wasn't fully clothed. So, might I
have been exposed for a short period? You
don't have to have been exposed regularly.
Just once.
5. It wasn’t a mosquito. Try this:
So, are you
absolutely, 100% sure it was a mosquito bite?
6. The scientists who’ve tested DEET extensively
and repeatedly for over half a century have all been lying when they tell us
DEET works. Or they’re
shape-shifting lizards. Or it’s
something to do with Bill Gates, or 5G, or vaccines. Or something.
So, are the conspiracy nutters right?
7. There’s an omnipotent, all-powerful God, and I’ve upset her very, very much. So, are you out of favour with God?
Consider each of the above possibilities, and for each one, consider firstly the likelihood that it happened. As I say, maybe put them in order.
Now, take each one in turn, and let's say that's what
actually caused your bite. Now, what
would you say would be the most logical response to that happening. For how many would that be “Stop taking DEET
and try something else which is completely scientifically unproven. Probably just something I read on the
internet, because that has a track record of rock-solid accuracy."
For how many should it be “Continue taking DEET, I must
just have made a mistake.”
I'd say, for numbers 1-5, the logical response would be that
it wasn't a case of DEET not working, it's some other error, easily done. In which case, it'd be daft to stop taking
DEET, and for more sensible to try to eliminate the chance of error, as much as
is humanly possible.
But if you're still not convinced, for how many would the
logical response be “I’ll try something else which has been tested and
proven to work, like PMD, picaridin, oil of lemon eucalyptus, or IR3535"
and for how many would the logical response be to try something unproven, or
something proven not to work, before exhausting all the ones already proven to
work?
Actually, number 7 is my favourite…
Saturday, 15 July 2023
It works for me
When discussing the efficacy of various anti-mosquito remedies, quite often someone will suggest one which has been tested and shown not to work, and when this evidence is pointed out to them they'll say "Well, it works for me!" To be fair, that a compelling point - you get bitten, you try a remedy, you don't get bitten, therefore the remedy worked. It's very easy to see how powerful that is in any case, and particularly when it's happened to you.
I think it's important to look at this claim. In the first instance, and indeed almost certainly in every instance, the question should be "Did it work?" And there's no harm asking the question.
Scientific research into mosquito repellents has taken place constantly since the 1950s, and pretty much all suggestions have been tried and tested using accurate experiments and techniques. The onus is, therefore, on anyone making a claim to others that "It works for me" to explain why they believe it does, if the scientific evidence shows it doesn't. You have a stack of science on one side, a few people's experience (possibly our own) on the other, I think it's valid to just pause and ask what might be going on.
Okay, here are the standards expected in statistical research. Let's star with a binary claim - let's say a typical claim that taking a particular tablet (garlic, Vit.B) repels mosquitos.
A double-blind controlled test is necessary. This would probably involve three people. The first person wouldn't have any idea, or opinion. We'd take 2 (we'll start with 2) people, give one a garlic tablet, and the other a placebo. The two people involved wouldn't know which was which, nor which was preferred by the person conducting the experiment. The person who gave them the tablets wouldn't know which was which, just 'Tablet A' and Tablet B'. If we really want to get serious, we can make it a triple blind test, where the person who looks at the results doesn't know which is which either, they can just say A or B worked best. Only after everything is completed is the truth revealed.
At each day's end the subject's arms/legs would be studied and photographed, with any bites logged. The photos would be used to ensure any old bite wasn't counted twice.
For scientific standards of evidence we need to apply a little maths to the results. The experiment should be completed on 10 separate occasions. One of the two samples needs to clearly outperform the other at least 9 times out of 10; this could be done over 10 days. .At that point the efficacy of the successful product can be said to have been proven as working on that person (yes, it could then be said it "works for them") with a 95% degree of probability.
That's the maths. That's what is required in a binary to test to say something works with more than a 95% degree of certainty.
Anything less than 10 separate experiments, and there's not enough data for the test to be statistically valid. Anything less than 9/10 in favour of one product over the other is not considered to be proven. We haven't proven to anyone, not even to ourselves, to any accepted standard that it "works for me". To be clear, unless we've done the above, we've not even proven "it works for me" to ourselves.
Now that would be the basis for an experiment if, and only if, we expected everyone using a suitable repellent to never be bitten, and those without an effective repellent to always be bitten, but we know what's not true. It'd also true that some people are effectively co0mpletely unattractive to mosquitos, and never get bitten, whilst yet others are very susceptible, or highly susceptible, to bites. So we'd need to carry that experiment out with ten pairs of people, selected at random, and get the same at least 9 out of 10 times.
If you have no interest in carrying out the above experiments, that's fine. Frankly, I wouldn't be prepared to do so either, so I've absolutely no criticism of anyone who doesn't fancy it themselves. But in that case, the question is whether we should be offering "It works for me" as a counter-argument to properly conducted scientific trials. What we'd doing in that instance is saying "Ignore the masses of evidence from hundreds of correctly controlled tests, and instead listen to my view, which I'm not prepared to test to any accepted standards of accuracy."
Unless we've done the above, we haven't proven to ourselves to the required standard of scientific accuracy that the remedy in question works, even just for us, let alone anyone else. In that instance, we should not be making that claim to other people. And we certainly shouldn't be offering it as counter-evidence to properly conducted research.
And finally, let's say we've done all of the above, and it does indeed work for us. Even at that point, we've proven nothing other than that. There are some areas where we're a little in the dark with on mosquito repellents, and one of the things we don't know about is why some people attract more bites than others. We do know that there's quite possibly a genetic dimension to this, and that in turn may affect how different repellents work on you. However, we do know from other research which repellents work best for most people.
So, returning to our first experiment, if we conduct that, and find garlic or Vit.B works for us, this does not discredit the decades of research on the matter, it just shows we're an exception to the rule, an odd one out, possibly a genetic aberration.
In that instance, we really shouldn't be offering "It works for me". we should be saying "It works for me, but based on all the available evidence I'm the odd one out and it almost certainly won't work for you, and you should ignore my example - I'm the exception that proves the rule."
Tuesday, 26 July 2022
Avoiding and Treating Mosquito Bites - The Evidence
This blog post is a supplement to my other blog on the issue of avoiding and treating mosquito bites. The other has a more conversational tone, but this one is just the evidence. So this is just for the 'heavy reading' which supports what you'll find in the other blog.
DEET works. It just does. It's the best (or at worst the equal best) mosquito repellent, and in its higher concentrations, lasts longer than most others. The other two proven repellents are Picaridin and Oil of Lemon Eucalyptus (or OLE). Note - NOT 'Lemon Eucalyptus Oil' - that's something quite different. Also, the rare IR3535 is good, though that's found more often in vaporisers (more on that later) than creams or lotions.
Links for DEET working, as well as Picaridin and OLE:
https://campushealth.unc.edu/wp-content/uploads/2016/07/InsectProtectionJuly-2016.pdf
And comparisons with IR3535:
Link for 'Lemon Eucalyptus Oil' (sometimes called 'Lemon Eucalyptus Essential Oil') vs 'Oil of Lemon Eucalyptus' (OLE). Please note the essential oil isn't very good.
https://www.hebebotanicals.co.nz/mosquito-repellents/
Note that DEET is often referred to as the 'Gold Standard', but different tests variously show one or other of these four as being marginally better than the others.
Regarding Avon Skin So Soft. Avon used to sell this product under the sub-banner 'insect repellent'. However, they've stopped doing so at the same time as they stopped using Picaridin as an ingredient. You can check this yourself; just go to Avon's website and search 'Skin So Soft'. These are the results. None now say 'insect repellent' on the bottle, which in itself should flag up a warning.
https://avon.uk.com/search?type=product&q=skin+so+soft
Several of the products no longer state their ingredients, but those that do show that Picaridin has been replaced with 'citronellol'.
https://avon.uk.com/products/skin-so-soft-original-dry-oil-spray
Citronellol works, but only for a very short time, and is simply not reliable. Given that there are several alternatives available, it would appear to be deliberately contrary to opt for a less effective repellent. Details here:
https://www.fitfortravel.nhs.uk/advice/malaria/mosquito-bite-avoidance
You cannot repel mosquitos by eating garlic tablets...
https://pubmed.ncbi.nlm.nih.gov/15752181/
...or Vitamin B, or bananas (garlic here, too)...
...Vitamin B again...
https://pubmed.ncbi.nlm.nih.gov/16033124/
...or marmite...
https://mobile.twitter.com/LSHTM/status/1539630785078099969
...or devices which emit ultrasonic sound...
...or bracelets/wrist bands...
...or citronella candles...
Here's a video covering many of the above:
By the way, whilst ultrasonic plug-ins don't work, you can buy vaporisers containing IR3535, and other repellents. Scroll down here to "What else is bugging you" Q5.
More here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549831/
Note, 'coils' that are left to burn slowly are effective, but there are concerns about their safety. As there are alternatives, I see no point taking the risk.
More:
https://www.nea.gov.sg/dengue-zika/stop-dengue-now/types-of-spatial-repellents
Scented toiletries attract mosquitoes:
https://www.mrmr.biz/mosquito-control-tips-mosquitoes-human-scents/
Interestingly, if you've ever wondered why you get bitten but your partner doesn't, your attractiveness to mosquito bites may be up to 85% genetic.
https://www.webmd.com/allergies/features/are-you-mosquito-magnet
But there's nothing you can do about your genes.
Mosquitos appear to be attracted to CO2 and alcohol. I strongly advise not exercising too heavily whilst on holiday, but avoiding alcohol is not an idea for which I'm prepared to offer the oxygen of publicity.
Taking one-a-day antihistamines may reduce swelling and itching if you are bitten, with cetirizine being best:
Applying various treatments after being bitten can help reduce swelling and itching, including ammonium solution (as found in After Bite):
https://pubmed.ncbi.nlm.nih.gov/9689301/
Or try calamine lotion or hydrocortisone cream:
https://www.geelongmedicalgroup.com.au/2018/11/how-to-get-rid-of-mosquito-bites-asap
I prefer the After Bite 'pen' as it's easiest to carry and least messy to apply. You just take the top off and press the exposed 'pen' on the bite. No need to run cream in, getting it all over your hands, etc.
I hope I've covered everything. In each case I've chosen just one or two links, but you'll find many more in most cases.
I've tried to limit links to reputable studies and reliable sources. If you want, you'll e able to find sites proposing quack remedies, and some look both professional and plausible. But if something claims to work, look to see if there's been repeatable, peer-reviewed, double-blind test to support it.
Sunday, 16 May 2021
Covid Conspiracies - The Questions That Need Answering (before you're daft enough to believe in them)
- Extremely nasty right wing dictators like Bashar Al-Assad of Syria, and Teodoro Obiang Nguema Mbasogo of Equatorial Guinea
- Very right wing, nominal 'democracies' like Jair Bolsonaro of Brazil. Not particularly 'on message' with Covid, and currently playing catch up, but he admits it exists and is dangerous
- Centre-right democratic leaders like Trump in the US or Johnson in the UK. Again, not always as 'on message' as you'd like, but spending (for Trump, 'spent') billions, and curtailing freedoms in a way which doesn't sit well with their general political philosophy. But they're still on board.
- Centre-left democratic governments like those currently in power in France, Italy and Finland
- Progressive left wing governments like Jecinda Ardern's in New Zealand.
- Hard left democratic governments like those in Greece
- Very left wing nominal 'democracies' like Venezuala
- Extremely nasty left wing dictatorships like North Korea
What do they all have in common. They all believe there's a threat to public health from Covid, to the extent that they've brought in unusual and extraordinary measures. That's right. The communists agree with the nazis. The Thatcherites agree with the Corbynistas. The Israelis agree with the Palestinians. The religious Islamic leaders agree with the secular west.
Monday, 22 March 2021
Why It's Important to Have a Covid Vaccine
When I first opened this blog, I said it was because the space constraints of FaceBook made it difficult to discuss some matters in the detail they require. The necessity of having a Covid vaccine is one such instance.
It can be a tricky, emotive, and complicated topic, so I'll try to keep this as honest and simple as possible So the following numbers are purely illustrative. They're not be taken as accurate, pure science, but as an idea of why vaccination is important.
Firstly, let's look at a virus, any virus. There's a lot of talk about the 'R' number. That's just a measurement of how many people a person, on average, will pass the virus on to. So, if a virus has an R of 1, what does that mean? It means that. if we don't change our behaviour (social distancing, etc.), if 10,000 people have it today, then 10,000 will have it tomorrow, and 10,000 will have it in a week, and 10,000 will have it in 6 months.
Some of the original 10,000 won't have given it to anyone. Some will have given it to 3 or 4 people. But, on average, each one person will have infected one other person.
But what if it's a nasty virus and the R number is 3? That means that each of those people gives it to 3 more. So now, those 10,000 people become 30,000. That then becomes 90,000. That becomes 270,000. That becomes 810,000. That becomes 2,430,000. That becomes 7,7290,000. That becomes 21,870,000. And that becomes 65.5 million. The entire population of the UK infected from a starting point of 10,000 people, in 8 steps. Of course, it'd never come to that, but that's just to illustrate how fast things can change.
But let's say we could reduce that. Let's say the R number was reduced to 0.75. 10,000 would become 7,500. Then 5,625. Then 4,219. Then 3,164. Then 2,373. Then 1,780. Then 1,335. And then 1,001. That's what we've done with the Coronavirus with lockdown. We've not got R down to 0.75, but we've got it below 1 by closing the pubs.
So how do vaccines help? Some say that there's no point in being vaccinated against a virus if it's not 100% effective. Well, let's say vaccines reduce your chances of getting the virus by 75%. 3 people out of 4 who would have got the virus no longer do. But 1 out of 4 does. That means those 10,000 people, instead of passing it on to 30,000 people, will only pass it on to 25% of those. Which is 7,500. So the R number has come down from 3 to 0.75, because of the vaccine. So for a virus with an R of 3, if the vaccine is 75% effective, it reduces the R to 0.75. Instead of growing by x3, it's shrinking by a quarter.
But what it some people aren't vaccinated? How many people do we need to be vaccinated to control that virus? Well, we know that we need enough for the R number to fall below 1. Remember, an R of 1 means the numbers are stable, above 1 and the numbers with it are growing, below 1 and numbers are shrinking. We said that the virus has an R of 3. So 200 people give it to 600 more people. If everyone were vaccinated with a jab that's 75% effective they'd only give it to 25% of those 600, so that's 150. 200 becomes 150, that's an R of 0.75.
But let's say a quarter of those 600 weren't vaccinated. 150 would get it from not being vaccinated, and 112 (25%) of those vaccinated would get it, that's a total of 262. So 200 people pass it on to 262. So if the virus has an R of 3, and the vaccine is 75% effective, and only 75% of people get jabbed, the R remains above 1. And if we don't want the virus to spread, we need to keep the pubs shut.
Let's try some more sums. If 90% are vaccinated, 60 of the 600 would get it because they weren't vaccinated, and 135 who were vaccinated would get it.
60 + 135 = 195. 200 people pass it on to 195. The R has just dipped below 1.
So we would need 90% of people to be vaccinated to bring the R below 1. Or alternately, keep some lockdown measures in place.
So that's a theoretical virus. What about the Coronavirus?
It's very difficult to say with any degree of accuracy where we are with Covid, because we're nor completely sure of the virus's true R number, nor exactly how more infectious the new variants make it, nor exactly how much the vaccines prevent spread.
But we do know that the virus has an R above 1 (a long way above 1). And we do know the variants increase this. And we do know vaccines reduce your chances of passing it on.
And we also know that we've only been able to bring the R down to below 1 with some pretty hefty changes to our lives.
And we do know:
- The R number needs to be below 1
- This virus has a natural, unchecked R of way over 1
- There are only 2 ways to bring the R number down (a) lockdown measures, and (b) vaccination
- The more people who are vaccinated, the fewer lockdown measures are needed.
- The fewer people vaccinated, the greater the number of lockdown measures must remain