Imagine for a moment that you are stuck on an island with a few dozen other people. The island has a spring that serves as its only source of fresh drinking water. By some stroke of luck, the island also has a safe, secure, sanitary porta potty that sits a couple hundred feet from the freshwater spring (humor me; you saw Cast Away). You and the other strandees have collectively decided that the porta potty is safe and that it is open and free for everyone on the island to use.

In spite of this astonishingly lucky set of circumstances, a fellow desert-islander named Chuck tells the group that he’s philosophically opposed to using the portable toilet and that the only comfortable place for him to have a bowel movement is on a stump a few feet away from the freshwater spring. Chuck is not differently abled. There are no poisonous plants or insects in the area of the toilet. He has no history of an allergic reaction to the toilet seat in the porta potty. Everyone points out to Chuck that by doing this he will endanger the lives of everyone else through contamination of their drinking water with his feces. An epidemiologist in the group (again, what a stroke of luck!) calculates that by continuing to defecate near the spring, Chuck will give between two and three people a diarrheal illness, and given the tenuous nutritional situation on the island, one of them may die. Chuck is unconvinced, and continues to use the spring as his private latrine.

Now imagine that a vaccine to a virus that is currently the number one cause of death in the United States is available for free. It appears safe. It cannot give you the virus, as it contains no intact virus. By getting the vaccine you will drop your chance of illness by more than 90%. More importantly, you may well save someone else’s life by getting it, just as Chuck might save the health of his island-mates by pooping in the toilet. That vaccine, obviously, is one of the newly available vaccines against SARS-CoV-2, the virus that causes COVID-19.

Given this, we can only conclude that anyone who has access to COVID-19 vaccination and for whom vaccination is not medically contraindicated has a moral obligation to undergo vaccination in order to contribute to herd immunity. The end. It is a classic utilitarian problem: unless the individual cost of being vaccinated is so high that it outweighs the expected negative effect on the aggregate wellbeing of others, we are obligated to be vaccinated. And if you think a possible mild fever for two days outweighs the current death rate of more than 3,000 people per day in the United States, we operate in different moral universes.

This calculation applies not only to the elderly, whose COVID-19 infection fatality rate may be more than 10%, but to the youngest people approved to get the vaccine (sixteen year-olds) who have an infection fatality rate of less than 0.01%. Because the spread of the virus, often asymptomatically, among young people is the single biggest threat to the health and life of the elderly. Fortunately, since SARS-CoV-2 is not as easily transmissible as extremely contagious viruses like measles, and since the vaccines are extremely effective, the number of vaccinated people needed to achieve “herd immunity” is smaller than some other vaccinations: probably around 75-85%. But we’re operating on the razor’s edge right now: our drinking water-contaminating friend Chuck is the 16% of the population who still state they will refuse a COVID-19 vaccine.

If you have a known severe allergic reaction to a prior vaccine, then you should probably wait to be vaccinated against SARS-CoV-2. But true allergic reactions to vaccines are unusual. By my back-of-the envelope count, only three people out of many tens of thousands already vaccinated have reported allergic reactions.

So please get vaccinated as soon as you can. And please encourage your employees to get vaccinated. It is our only path out of the sticky mess we’ve been in since March.

As the Medical Director of the Kansas Business Group on Health I’m sometimes asked to weigh in on hot topics that might affect employers or employees. This is a reprint of a blog post from KBGH.