Herd immunity

When studying rates of infections, notably with measles, researchers have seen that in cases where a sufficiently large proportion of a population has been immunised or developed protection against a disease then infection rates also reduce in unprotected members of the population. In other words, the unprotected members appear to receive some indirect protection from the protected members of the population. This effect is known as herd immunity and is a tantalising goal for reducing the prevalence of epidemics.

While appealing in theory this article in Nature provides Five reasons why COVID herd immunity is probably impossible . These include:

Uncertainty around whether vaccinations prevent transmission. For example, herd immunity works when diseases can't be passed between protected members of a population to the unprotected. With COVID-19, vaccines seem to reduce symptoms but may still allow transmission.

It's also challenging to get vaccines evenly to all areas. These combined with complications brought by new variants, immunity fading before widespread vaccination is achieved, and people changing their behaviour — say, mixing more widely — once they've received some protection, means COVID-19 may be more likely to be something we live alongside rather than eradicate.

Also see: the Swiss cheese model

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Published 25 Apr 2021

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What is Naismith's Rule for calculating walking time in the mountains example explained with a mountain ridge with hikers and lines for the horizontal distance and time and ascent and time

Naismith's Rule for mountain hiking time

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Eponym

Naismith's Rule provides a quick estimate for hiking time in the mountains, intended for "easy expeditions." It suggests: 1 hour for every 3 miles (5km) walked +1 hour for every 2,000 ft (600m) of ascent For example, suppose your hike covers 6 miles with 2,000 ft of ascent. In that case, Naismith's Rule suggests allowing 3 hours total—2 hours for distance and 1 hour for elevation. Origins of Naismith's Rule William Naismith was a Scottish Mountaineer born in 1856. He spent years trekking in the Highlands and was, to be fair, probably made of nails. In the Scottish Mountaineering Club Journal in 1893, he wrote: "...a simple formula, that may be found useful in estimating what time men in fair condition should allow for easy expeditions, namely, an hour for every three miles on the map, with an additional hour for every 2,000 feet of ascent." The Scottish Mountaineering Club Journal, Vol. II, September 1892, No.3, p.136 (pdf) Does Naismith's Rule Work? A figure I learned that's stuck with me is that a brisk walk is around 4 mph. But that's actually pretty fast and wouldn't apply on a mountain trail and certainly not hiking up a mountain. So I've run into the challenge myself when planning a trip in the mountains of how to guess how long a hike will likely take. From a recent hike—where I made sure to run through the full kitchen table survival skills and 10 essentials before leaving—limited daylight was a safety consideration. So knowing how long the hike might take was really important. Incidentally, there's a rule of thumb, literally, for estimating remaining daylight. Lots of people have put Naismith's Rule to the test, including me, and though it's a slightly optimistic metric, it's a starting point. On my recent hike, we were slightly over, but not by much. Adjusting Naismith's Rule To adjust for your circumstances, add time for: Tricky or technical terrain Steep descents High altitude Lunches and snack stops Not being "in fair [physical] condition" in the view of a rugged mountaineer from Scotland in the 1890s Heavy packs, poor weather Getting lost Walking with children Photography, bird watching, animal spotting Time to stop and enjoy the views Sitting and sketching Presumably, if the hike was really long, you'd slow down The Unexpected So, there are many reasons why Naismith's Rule may be on the light side. But it's a decent place to start from. Killian Jornet Laughs in the Face of Naismith's Rule Someone for whom Naismith's Rule definitely doesn't apply is the incredible Killian Jornet, whom I watched in the beautiful documentary Déjame Vivir on Netflix. Footage of him running along knife-edge ridges at the top of the Alps is breathtaking. In 2024, he hiked all 82 peaks above 4,000m in the Alps in 19 days without using motorized vehicles between them 🤯. Let me know if you give Naismith's Rule a try! Related ideas Also see: The Fun Scale The 10 essentials Kitchen table survival skills Take photos of maps before a hike Use a compass Rule of thumb for remaining daylight Kaffikok — the time you can travel before needing another cup of coffee Time hierarchy Isochrones Human pace I made some prints and products with and without the text in case, like me, you like a peaceful mountain ridge without any rules…Naismith's Rule provides a quick estimate for hiking time in the mountains, intended for "easy expeditions." It suggests: 1 hour for every 3 miles (5km) walked +1 hour for every 2,000 ft (600m) of ascent For example, suppose your hike covers 6 miles with 2,000 ft of ascent. In that case, Naismith's Rule suggests allowing 3 hours total—2 hours for distance and 1 hour for elevation. Origins of Naismith's Rule William Naismith was a Scottish Mountaineer born in 1856. He spent years trekking in the Highlands and was, to be fair, probably made of nails. In the Scottish Mountaineering Club Journal in 1893, he wrote: "...a simple formula, that may be found useful in estimating what time men in fair condition should allow for easy expeditions, namely, an hour for every three miles on the map, with an additional hour for every 2,000 feet of ascent." The Scottish Mountaineering Club Journal, Vol. II, September 1892, No.3, p.136 (pdf) Does Naismith's Rule Work? A figure I learned that's stuck with me is that a brisk walk is around 4 mph. But that's actually pretty fast and wouldn't apply on a mountain trail and certainly not hiking up a mountain. So I've run into the challenge myself when planning a trip in the mountains of how to guess how long a hike will likely take. From a recent hike—where I made sure to run through the full kitchen table survival skills and 10 essentials before leaving—limited daylight was a safety consideration. So knowing how long the hike might take was really important. Incidentally, there's a rule of thumb, literally, for estimating remaining daylight. Lots of people have put Naismith's Rule to the test, including me, and though it's a slightly optimistic metric, it's a starting point. On my recent hike, we were slightly over, but not by much. Adjusting Naismith's Rule To adjust for your circumstances, add time for: Tricky or technical terrain Steep descents High altitude Lunches and snack stops Not being "in fair [physical] condition" in the view of a rugged mountaineer from Scotland in the 1890s Heavy packs, poor weather Getting lost Walking with children Photography, bird watching, animal spotting Time to stop and enjoy the views Sitting and sketching Presumably, if the hike was really long, you'd slow down The Unexpected So, there are many reasons why Naismith's Rule may be on the light side. But it's a decent place to start from. Killian Jornet Laughs in the Face of Naismith's Rule Someone for whom Naismith's Rule definitely doesn't apply is the incredible Killian Jornet, whom I watched in the beautiful documentary Déjame Vivir on Netflix. Footage of him running along knife-edge ridges at the top of the Alps is breathtaking. In 2024, he hiked all 82 peaks above 4,000m in the Alps in 19 days without using motorized vehicles between them 🤯. Let me know if you give Naismith's Rule a try! Related ideas Also see: The Fun Scale The 10 essentials Kitchen table survival skills Take photos of maps before a hike Use a compass Rule of thumb for remaining daylight Kaffikok — the time you can travel before needing another cup of coffee Time hierarchy Isochrones Human pace I made some prints and products with and without the text in case, like me, you like a peaceful mountain ridge without any rules

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