Backpacking and Thru-Hiking during COVID-19

Backpacking Responsibly During the COVID-19 Pandemic?

Are you thinking about backpacking or thru-hiking during COVID-19?  Are you wondering if you can do it safely?  If the goal is to eliminate all risks, the short answer is: No. Don’t go backpacking.  The safest and easiest way to reduce risks to yourself and to others in society is to not go backpacking.  It’s not “essential,” and therefore will unnecessarily increase the risk that you could contract/spread COVID-19.

However, people are going backpacking.  There’s indication that backcountry trips have only experienced a decline of around 40% since COVID started.  That means that we need strategies to mitigate the spread of COVID that go beyond the “abstinence-only” strategy for backpacking.

Further, there has been very little effort made by the backpacking community to quantify or discuss risks of backpacking during the COVID-19 pandemic.  We need to better understand the elements of backpacking that need to change compared to the pre-COVID status-quo.

As the pandemic may be prolonged for some time, I’ve started to identify and quantify societal risks and mitigation strategies.  To that end, I have created the PIPP strategy as an initial framework to begin the discussion of how to responsibly go backpacking during COVID-19.

If you are going to go backpacking, there are a number of high-risk and low-risk activities or interactions that could occur from a COVID-19 perspective.  It is important to understand these risks, and to assess and adopt risk mitigation strategies.  I’ve tried to characterize the costs of not adopting certain strategies to improve our understanding for what might be acceptable societal risk if you do decide to go backpacking.

What new risks does COVID-19 bring to backpacking?

For COVID-19, every new point of contact with someone that could be infected presents a possible exposure pathway.  As such, it is important to minimize the number of contact points, and the duration (time spent) for each contact.  For backpacking during the COVID-19 pandemic, there are well-defined interactions that may result in transmitting or being infected by COVID. The table below highlights points where one might transmit COVID or be exposed to COVID as part of the traditional backpacking process.  Exposure risk is approximated based on how long an interaction is likely to occur, and how easy it is to physically distance from a possible source of infection for that interaction:

Point of Risk	Reason for Concern	COVID exposure risk	Can this be avoided?	Mitigation Strategies
Purchasing food/supplies	You may be exposed to COVID at the time, or expose others to COVID if you’re infected	Moderate	Yes (would be the same risk as not backpacking)	Do backpacking food shopping during the same period you are doing typical food shopping. Practice proper mask use + hand washing
Medical evacuation from the trail	A medical evacuation during the COVID pandemic will directly put you and your evacuation team at risk of COVID infection	Extremely high	Almost entirely	Completely Isolate for 2 weeks before your trip   Avoid all possible points of contact when going to a trail head   Do not partake in hiking/backpacking activities likely to increase your chances of needing an evacuation – you should hike on established trails, and you should not hike outside of your experience-level or comfort.
Interacting with other hikers on the trail	If you are backpacking with others, or pass others on a trail, you may expose yourself or others to COVID	Low	Yes	Social distance from all other hikers.  Minimize duration of contact and maximize the distance between you and others outside of your isolation group.  Use hand sanitizer/soap.  Do not share supplies or food.
Getting to or from a trail head	Shuttling and other forms of public transportation, like hitchhiking, are often strategies used to get to or from a backpacking destination	Extremely high	Yes	Avoid using all transportation that will be with individuals that are not part of your isolation group
Surface contact	Surfaces may potentially act as vectors for infection	Low	Yes	Do not touch surfaces or use things that other people may have touched or used (e.g. shelters).  Limit duration of exposure.

Based on the above risk outline, it seems very possible to come up with a backpacking trip that poses exceptionally low risk to yourself and to others.  It is even possible to design a trip that is likely to pose no additional risk to the community relative to the counterfactual of not going backpacking. 

Out-and-back backpacking through COVID-19 (no resupplies)

The above table suggests that the most probable scenarios for exposing yourself or others to COVID-related risks as a result of backpacking is from:

• Transportation to/from a trail head
• The risk of infecting others if something goes wrong (medical evacuation)
• Food/supply shopping

You can take proactive measures to avoid transmission of COVID-19 to others prior to starting a backpacking trip.  This risk can almost entirely be mitigated through isolation measures before a backpacking trip.  Additionally, transportation risks for many trips can be entirely mitigated through well-planned transportation strategies that use only your own personal vehicles, or vehicles of those within your household/isolation group.

Other precautions can be used to further eliminate the likelihood of infection through surface contact, and therefore spreading COVID when re-entering society.  To reduce risks of contracting COVID-19 while in the wilderness:  you should avoid using shelters and should also avoid touching surfaces.  If you do touch surfaces, you should wash/sanitize your hands after contact (practice good LNT etiquette). 

To further avoid risks of spreading COVID in the event that you need to be evacuated from your trip, food should be purchased prior to an intentional isolation period. You should isolate yourself completely after purchasing food and supplies and prior to going on the trip.  For a short trip, you should isolate for the suggested 2-week period prior to the trip.  This will substantially reduce the risk that you are infectious, and therefore mitigate the risk of spreading COVID to others in the event you need to be evacuated. Additionally, if you are going on a longer backpacking trip, it is likely a good idea to get tested for COVID before you go, so that you can further decrease the likelihood that you will become symptomatic in the wilderness, unnecessarily increasing the probability that you will need a medical evacuation.

For short-duration trips, planning should allow you to follow a “PIPP” procedure to avoid exposing others to COVID:

1. Purchase necessary backpacking food and supplies (possible COVID exposure) prior to an isolation period.
2. Isolate yourself from others for a period of time (ideally 14 days) to remove the risk of infecting others and spreading the disease.
3. Plan to travel to the trailhead without any additional points of contact, and make sure you have an exit strategy if you fall ill while on the trail.  This exit strategy should not involve contact with other people.  If your exit strategy requires contact with other people, make sure you have established a consensual agreement with someone else that can fetch you while minimizing contact with others prior to embarking on your trip.
4. Protect yourself and others when hiking.  Avoid interacting with others that are outside of your isolation group, and carry a mask, soap, and hand sanitizer for situations where you will be unable to substantially distance yourself.  Interaction duration should be kept to a minimum (the shorter the duration of interaction the less likely you are to infect others or be infected).

Long trips or Thru-hiking through COVID-19

The table above provides a good outline for beginning to understand the risk of backpacking and ways to decrease that risk.  However, it does little to quantify risks, and does not address longer backpacking trips or thru-hikes.  A short backpacking trip can follow the PIPP strategy to substantially reduce risks (they cannot be fully eliminated).  A longer backpacking trip that has resupplies can also follow the PIPP approach.  The key difference between a short trip and something like a thru-hike is how one might establish an “isolation” period.  When thru-hiking, isolation will take place on the trail. 

In a world where capacity and weight did not matter, you would simply be able to follow the PIPP strategy perfectly, and quarantine after picking up enough food to last the entire duration of the thru-hike.  Because it is unlikely you can carry sufficient food for the entire hike, a different strategy can be considered: shortened isolation between resupplies.  Although CDC guidelines suggest an isolation period of 2 weeks, the actual infectious profile of the virus is substantially different.  I used data from He et al, 2020 to create an infectiousness profile.

As you can see from the curve, infectiousness is much higher in the first couple of days after you’ve been infected than it is later on.  In fact, roughly 50% of infectiousness will occur before you even show any COVID symptoms.  The He et al study suggests that symptoms manifest for most people part way through day 5.  (Most people become symptomatic between day 4.1 and day 6.4).

Because many people are likely going to try to backpack between resupply points, there is a delicate balance between establishing an isolation period that is both achievable while on trail, and that can substantially reduce the risks of and associated social costs of spreading COVID.  I have modeled what this looks like – there are details at the end.  In general, a socially-responsible thru-hiker should try to:

1. Reduce the chance they expose someone to COVID if they’ve been infected, and
2. Reduce the distance they will need to travel to evacuate if they do show symptoms

As people are unlikely to carry 14 or 20 days of food with them while embarking on a thru-hike, a thru-hiker will likely seek to reduce the amount of food they will have to carry between resupplies.

As discussed in the quantification section below, I conducted some social cost analysis to determine how to balance the risk of spreading infection with the desire to minimize duration between resupplies.  The minimum duration of time between resupplies should be 6 days. 

If you assume every resupply point likely results in a new COVID-19 exposure, then you have to wait 6 days before your next resupply.  This can be circumvented through the use of contactless resupplies (e.g. package drops/food caches).  As most people are likely to show COVID symptoms within 4.1 to 6.4 days from the time they were infected, a 6-day resupply also means that you can be close to an evacuation point if you did contract COVID.  By day 6 your viral load will also be substantially reduced from its peak duration (a couple days prior to when symptoms manifest), which lessens the odds that you will spread COVID-19 during your resupply (if you’re asymptomatic), or while evacuating.  My modeled social costs of thru-hiking using different resupply strategies is detailed in the following figure:

To responsibly thru-hike during the pandemic, a PIPP strategy looks like this:

1. Purchase food prior to starting your hike
2. Go into an isolation period for at least 14 days prior to your hike
3. Take a test to ensure you do not have COVID
4. Travel to your destination responsibly.  Do not hitchhike, do not subject yourself to any points of exposure prior to starting your hike (if this can be avoided)
5. Set up resupplies for every 6 days.  Do not rush a resupply.  If you end up at a destination before 6 days is up, you should wait until the 6-day trail-isolation period has expired before journeying into town for a resupply.
6. Avoid all hitchhiking into and out of town, as this poses substantial new risks of exposure
7. When resupplying, minimize the amount of time you spend in town.  Do not spend more than 45 minutes, cumulatively, within any indoor location.  Make sure the indoor location has fewer than 3 people per 2,500 sq.ft (250 m²)
8. Wear a mask properly (fully covers nose and mouth) during any instance where you are inside, or if you cannot substantially distance from others
9. Carry sufficient masks such that you can properly dispose of it after 2-hours of use, while still being able to have sufficient masks for resupplies and emergency evacuations
10. Be aware of the local COVID situation in the areas that you stop in for resupplies

Concluding Remarks

Is it worth backpacking or thru-hiking during COVID?  It really depends on how you do it.  My analysis indicates that it is possible to do it responsibly.

If you are going on shorter backpacking trips, completely isolating yourself for 2-weeks after you purchase supplies should substantially reduce risks of spreading COVID to others in the community.  For thru-hikes or trips with resupplies, you should aim to isolate yourself (by being on trail) for at least 6 days after a possible COVID exposure (such as buying supplies). If you follow a 6-day resupply schedule for a thru-hike, you can likely backpack safely without exposing communities to risks that exceed the individual benefits of thru-hiking.

Even if you are distancing at 6-day intervals and limiting resupply stops to 45 minutes, the expected social cost is around $6,000.  Would you be willing to forego an additional $6,000 beyond your budgeted cost of thru-hiking?  How long would you have to delay a thru-hike for to offset an additional $6,000 in personal costs?

If you decrease the time between resupplies from 6-day intervals, or increase the time you spend in towns, or fail to isolate yourself or use protective masks, then the social costs grow exponentially.  For “pre-COVID” backpacking behaviors, if not changed during the COVID pandemic, I estimate that social costs of thru-hiking are in far excess of $20,000.  This exceeds what most people are willing to spend on a thru-hike to begin with.  That means that you should not do a thru-hike during COVID without substantial modifications. If you really intend to go thru-hiking, it may be reasonable to fully offset any social costs by donating an equal or greater value (~$6,000) to communities and search and rescue teams surrounding your thru-hiking corridor. I estimated that the in-town social cost is only ~$1,000 for a thru-hike when practicing the 45-minute, 6-day resupply intervals discussed, while the risk of needing to evacuate for medical reasons largely makes up the difference (even if you can get to the trail head, are you going to make extended contact with fewer than 3 people to get back to safety/recover from an injury?)

After properly considering all of that, and realizing that hiking with 6-or-more days of food between resupplies might very well be miserable, and that you will be unable to socialize with others, bathe indoors, or spend any meaningful amount of time inside (no grid electricity), would you still value thru-hiking at an additional $6,000 beyond what you had already budgeted?  Additionally, many thru-hiking trails do not have resupplies conveniently located at 6-day intervals.  That also means you will likely need to spend time on the trail, outside of towns, to burn through excess food and wait through an isolation period.  If all of this sounds like something you will be able to adhere to, then maybe a thru-hike during COVID is a reasonable, low-risk activity.  If you think you can cut corners on 6-day wait times, or rely on hitchhiking to get into towns, then you had better look at something other than thru-hiking.

Other Considerations and Caveats

In addition to the quantification of COVID-related risks I detail below, the following things are also worth considering, especially in relation to how they may be able to reduce transmission risks

1. Using a solar charger instead of a battery bank can reduce the time you need spend in towns
2. You should avoid being indoors when in town.  This may mean you will not be able to shower for the duration of your hike. 
3. You should not stay in any sort of hotel or hostel, as risks would go up far higher than what I modeled
4. You should be prepared to fully end your trip if you are unable to adhere to the PIPP strategy
5. You may be able to create on-trail families if you are able to sync up on 6-day resupply/exposure intervals.  If you do this, it would be important to have only one person enter any indoor space, as exposure risks for others will otherwise increase exponentially
6. If you can practice LNT responsibly, having contactless package drops on the trail, or using food caches, may be a way to reduce the 6-day resupply duration
7. You should practice good hygiene with handwashing/sanitization before and after touching surfaces
8. You should practice social distancing with anyone else you meet on trail, and avoid prolonged contacts. 6-ft distance for 8 hours a day with someone you meet on the trail is still likely to be risky.  Keeping a 100-ft distance for 8 hours a day is much less risky.
9. You should get a COVID test to ensure you do not have COVID prior to embarking on a long trip
10. Evacuate from the trail if you experience any symptoms that may be COVID related.
11. You should probably carry a thermometer to regularly check your own temperature
12. You should carry a sufficient supply of surgical masks, kept in a waterproof and secure location. The supply should allow for all resupplies and emergency evacuations that you might have
13. Carry a satellite communication device so that you can coordinate on an evacuation plan with your consensual evacuation designee should it be necessary
14. You should be aware of the rates of COVID in the towns you plan to resupply at, and understand the various COVID-related restrictions that may be in place through areas you plan to travel in

Discussion on Quantifying COVID-related Risks (Modeling Details)

The model can be downloaded from here

The Purchase-Isolate-Plan-Protect (PIPP) strategy outlined above should be adhered to for any form of backpacking or hiking, including thru-hiking.  For thru-hiking, it will require substantially more planning and logistics to figure out how to safely isolate or safely purchase and gain access to supplies.  Additionally, safe exit strategies for a thru-hike may not be possible.  If you cannot create a safe exit strategy that does not increase the risk of exposing others, non-consensually to COVID, you shouldn’t hike. For many thru-hikes, it may be impossible to evacuate without substantially exposing communities to COVID. 

To better quantify these social costs and risks, especially in relation to thru-hiking, I created a risk model using data for the risk of COVID infection from He et al, 2020. These researchers used case data to generate a probability distribution for infectiousness of the disease over time.  The key outcome is that infection risk is highest prior to the start of COVID symptoms. The peak period of infectiousness is likely to occur up to 3 days prior to your own symptoms showing up.  After peak infectiousness, you have about half the remaining virility which continues to decrease over the rest of the infection period (~30% by day 6).

The figure I generated above shows how infectious you are likely to be relative to the point at which you were initially infected.  COVID symptoms manifest for most people part way through day 5.  (95% CI for symptomatic occurrence between day 4.1 and day 6.4).  I’ve used probability distributions to better understand risks to communities along thru-hiking trails.

What does this mean for backpacking?  It means that it is super, super important to isolate within the first several days of a possible COVID-exposure event.  For isolation in this context, it means you should avoid all contact with any other individuals, as you are at high risk of being a vector for the disease.Once isolated, you can wait to see if you have any COVID symptoms. The high-risk exposure events for backpacking primarily include food shopping, transportation with individuals you have not been in isolation with, and medical evacuations. If you do have symptoms (even mild symptoms) within the first 6 days from a possible exposure, the most important thing you can do is self-isolate for an additional 6-8 days to reduce the risk of infecting anyone else. 

From the above infectiousness curve, it is evident that you are likely to have greatly reduced your probability of spreading the infection by day 5.  However, you are only likely to know if you have symptoms, and therefore may have COVID, sometime after day 5.  For a thru-hike, or long-duration backpacking trip, this means that the earliest you should consider going into town for a resupply is Day 6.  If you do not have any symptoms by Day 6, it is likely that you either did not contract COVID, or are asymptomatic.  Research from Kim et al., 2020 suggests that approximately 20% of individuals will never manifest COVID symptoms even if they have the virus. This is non-negligible, and means you still could run the risk of infecting other people if you go in for a resupply on Day 6 yet do not have any COVID symptoms.  If you do have any symptoms by Day 6, you should evacuate, and end your backpacking trip.

If you are looking to thru-hike, I have created a table that details the probability of being infectious and not knowing based on the number of days since potentially contracting COVID at your last resupply.  I assume that every time you resupply/enter a town, you expose yourself to a potential COVID event and that this event is your only COVID exposure. For this to be the case, that means you must practice social distancing/complete isolation behavior while on the trail, and do not have any other potential exposure events.

Days between resupplies	Probability of being infectious + not having symptoms yet	Probability of being Infectious + never showing symptoms	Combined probability of being Infectious + not knowing at the time of your resupply
3	52%	19%	70%
4	30%	14%	44%
5	15%	10%	25%
6	7%	6%	13%
7	3%	4%	7%
8	1%	2%	4%
9	1%	1%	2%
10	0%	1%	1%
11	0%	0%	1%
12	0%	0%	0%

As you can see, by Day 6 the probability that you are infectious and do not know it will be around 13%.  That means that if you are going to partake in a resupply, there is a non-zero risk that you might infect others that you come in contact with.  To quantify the risk of unintentional infection, I looked at an aerosol modeling study by Vuorinen et al., 2020, which evaluates the risk of spreading COVID virus when indoors.  I used the values found in their figure 13d to approximate the risk of spreading infection when in town for a resupply.  This requires a set of assumptions for that resupply, and largely depends on:

1. the duration of time spent in indoor spaces, and
2. the number of people per area of an indoor space. 

The risk profile I’ve created is based on spending 45 minutes in town.  That 45 minutes is relegated to a resupply that takes place in a 2,500 sq.ft. space with only 4 people in it (3 people other than you).  Because the modeling that Vuorinen et al. conducted appears to be fairly linear, it means that doubling the time you spend in these locations, doubling the number of people in that area, or halving the size of the space will result in a doubling of the calculated risk.

For a 45-minute stop in a convenience store that has 3 other people (a total of 4 people), the estimated number of virus-laden aerosols that everyone will inhale, assuming only you are infected, would be ~3 particles.  Jayaweera et al, 2020 suggests that a critical load may be several hundred particles, while Vuorinen et al. assume a critical load is around 100 particles.  To interpret this, I’ve gone ahead and assumed that a critical, viral-laden load is likely when 100 +/- 30 particles are inhaled.  Assuming this risk of infection follows a normal distribution, there is a 0.1% probability that someone within the same convenience store will have gotten a critical load of virus-laden particle from you over a 45-minute time period.  This is not zero.

You might be thinking that a 0.1% chance of spreading the virus is pretty low risk and therefore reasonable, or even that 5x that risk level may be acceptable?  However, as humans we’re pretty terrible at understanding what a transmission risk like 0.1% translates to in terms of costs to society. 

To provide context, imagine that an individual does end up contracting COVID because of you, and ends up dying.  The U.S. currently has the value of a statistical life set at around $10 million dollars.  This is the value used for all sorts of policy decisions, and therefore is reasonable for assessing a backpacking decision.  Because there’s only a 0.1% probability that you may infect the person with COVID during your 45-minute convenience store run, that still means that entering that store creates an expected social cost of at least $10,000.  If you’re not deriving $10,000 in personal benefit from entering that store, then the costs far outweigh the benefits and you shouldn’t do it.   If that person contracts COVID because of you, and then goes on to spread it around the community before they manifest symptoms, then you are now responsible for substantially more than $10,000 in social damages.  Furthermore, 45 minutes in town is a very, very short stop-over compared to the amount of time many thru-hikers spend in towns.

I know some of you might be saying, “wait a minute, just because that person contracts COVID doesn’t mean they’re going to die.  That’s a much smaller percent!”  That is true.  I decided to account for this issue by looking at the incidence of hospitalizations (severe COVID cases).  I used the incidence rate for some higher-risk groups, like those typically found in small rural towns. The incidence of severe COVID cases for these groups is around 13%.  I consider all such cases to result in a meaningful loss of life, and therefore account for this as a social cost of $10 million dollars per each occurrence. Following a 45-minute, 6-day resupply guideline while using a mask results in a social cost to trail towns of ~$1,000, assuming towns are able to institute their own isolation/lockdown measures by the time 2 people in town are hospitalized with COVID.

Finally, I also decided to look at the case where you, yourself, end up with COVID while also sustaining an injury on the trail resulting in a medical evacuation.  I used wilderness evacuation incidence rates from Leemon and Schimelpfenig, 2003.  The probability of needing to evacuate from the backcountry is around 0.3% per day.  For an evacuation, I then assume you are likely to expose 3 people to COVID (those involved in evacuating you), with a 13% risk of hospitalization for each of these individuals.  I also assumed that if everyone is properly wearing masks, this may decrease the risk of infection by 50%, which is consistent with Cheng et al., 2020.

Taking all of that into account, I’ve generated the following figure:

This suggests that by practicing a PIPP strategy and resupplying every 6-days or longer, the social cost of your thru-hike may very well be worth it.  It also means that you will not be thru-hiking in a traditional, pre-COVID way.  It will require careful consideration of your resupply plan, and will require largely foregoing social activities with other hikers in the hiking community (one of the main motivations of thru-hiking).  It is important to consider these implications before jumping into a backpacking trip, especially a thru-hike.