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What is the R rate for other illnesses?

4 replies

NobblyBobble · 17/12/2021 09:54

I’m just wondering.
Things like Noro and the common cold which are very contagious?
Also things like hand, foot and mouth.

Genuinely curious.

OP posts:
Discustard · 17/12/2021 09:58

IIRC measles is 15?

CarrieBlue · 17/12/2021 10:01

From Wikipedia

What is the R rate for other illnesses?
rbe78 · 17/12/2021 10:02

This is quite a good article:
www.popsci.com/story/health/how-diseases-spread/
Typical seasonal flu is ~1.2, SARS is 2-5, measles is 12-18 (!!!)

The article makes the good point that the R value is a statistical model based on what would happen if the disease is left unchecked.

Which explains why everyone gets flu (beccause we leave it pretty much be apart from a few vaccines), but SARS didn't spread much at all (because it was almost immediately contained), despite SARS having a much higher R value.

And thank god for the MMR vaccine if measles is that contagious!!

chesirecat99 · 17/12/2021 11:12

The short answer is about 2-3 for all of them. Measles is 12-18.

The long answer is it's more complicated than that. There is more than one type of R number but during the pandemic the media has just been referring to the R number without specifiying the type.

The basic reproduction number of a disease R0 is the average number of people an infectious person infects in a population with no immunity that is homogenous (they all have the same number of contacts, behave in the same way). It's calculated from multiple studies observing the number of infections in different situations. It is an average and it is an estimate based on observations, which is why it is often expressed as a range. COVID is unusual in that we have actually been able to observe it in a population with no immunity, whereas that isn't the case for most diseases, so it is likely that calculations for R0 are more accurate than for some diseases. Of course, no population is homogenous, especially when it comes to the same number of contacts per person.

The other R number that is often talked about is the effective R number at the current time, called Re or Rt. Obviously the Re changes, unlike the R0. When the government/media talk about the R number being around 1 or 2 at the moment, they are talking about the effective R at the moment. Things that affect Re, are immunity, the number of contacts (people modify their behaviour when there is a bug going round), other preventative measures (eg things like washing hands or cleaning more when there is a norovirus outbreak) etc

Which leads back to the point that populations aren't homogenous. Schoolchildren, young adults, parents, adults without DC in the home, the elderly, all behave differently and have different average numbers of contacts. Immunity levels will be different in different subpopulations eg young children compared to adults compared to the elderly. So the Re may be different in a different subpopulations.

So, for example, the R number for norovirus on cruise ships (I've seen studies where it was estimated as 7) is higher than it is in the general population because people are inside a single space with the same group of people for a prolonged period, sharing toilets and sharing food from buffets.

I guess what I'm saying is don't draw too many conclusions from the R number without an in depth knowledge of the subject Grin

Also, there isn't much point comparing the R0 number of diseases transmitted in different ways if you are trying to compare them to see if we are "overeacting" to COVID. It's far easier to take mitigating action to reduce the Re of diseases that aren't airbourne or transmitted via respiratory droplets eg HIV has an R0 2-5 but you can easily reduce the Re through the use of condoms, whereas even though the R0 of the first wave COVID was a similar range, it took lockdowns to reduce the Re.

Also, you can't compare the R0 (the average number of people an infectious person infects in a population with no immunity that is homogenous) of a disease that is endemic (a constant number of cases) with a disease where there is a pandemic or epidemic (a higher number of cases than would be expected, case numbers aren't constant) and use that to decide that you should act in the same way for both diseases because the R0 is the same. You need to look at the Re and case numbers and the effect on public health.

Although that may not be why you are asking!

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