Table 3. Vaccination questions and corresponding explanation stimuli.

Question 1: How do vaccines work?
Metaphor 1: Castle	To understand the reason for vaccinations, it’s important to understand how vaccines work. Vaccines enable your immune system to do two things: (1) stop you getting infected by viruses or, (2) if you do get infected, end the infection itself because of the help your immune system has had from the vaccine. You can picture your body as a medieval castle. The castle is surrounded by an army of viruses trying to break in and take over. Your body’s first line of defense is an outer wall patrolled by a group of archers. These are your immune system’s antibodies. If they can hold the viral army off, then you won’t get infected. But if the antibody archers are overwhelmed, then the virus can break through. Once the virus is in the castle, you have an infection. However, all is not lost. You still have elite troops inside the castle. These are your memory B and memory T cells. If your outer walls are breached, these elite cells are inside ready to lead the charge and repel the hostile invaders. Vaccines train your body’s troops, including both the archer-antibodies and the inner cell warriors that react to an infection. However, the antibodies that patrol the outer wall sometimes forget their training. That is when the vaccine’s effectiveness wanes, and you may be infected even if you had previously been vaccinated. But the memory cells inside the inner castle are still there and can get organized very quickly to repel any invaders who have entered the castle. That is when a vaccine protects you from serious illness and death, even if not from infection. For viruses that won’t go away or that even change over time, boosters can strengthen your defending army. Boosters not only ensure there are enough archers in position defending the outer wall, they also provide the elite troops inside the inner castle with updated weapons training so that they are prepared to take on any potential invaders. The archers and troops might still be able to do their job without boosters. However, since boosters typically contain updated information about the virus’ new strengths and weaknesses, the archers and troops who face the infection without boosters are disadvantaged, with fewer resources and less knowledge than those who received the vaccine booster.
Metaphor 2: Bank	To understand the reason for vaccinations, it’s important to understand how vaccines work. Vaccines enable your immune system to do two things: (1) stop you getting infected by viruses or, (2) if you do get infected, end the infection itself because of the help your immune system has had from the vaccine. You can picture your immune system as the high-quality security measures surrounding a bank. The first line of protection from burglars is the security cameras monitoring the doors and windows. These are your immune system’s antibodies. If they detect the burglars and trigger the alarm, then you won’t get infected. But if any of the cameras fails, then the virus can get in. You now have an infection. Any cash stored in the bank could quickly be stolen. However, all is not lost. You still have a team of security guards inside the bank. These are your memory B and memory T cells. If the bank is broken into, they are ready to lead the immunological charge to stop the burglars. Vaccines train your body’s security-measures, including both the security camera antibodies and the inner cell guards that react to an infection. However, cameras can fail if they have not been updated for some time. That is when the vaccine’s effectiveness wanes, and you may be infected even if you had previously been vaccinated. But the team of security guards is still there to deter an infection and can get organized very quickly to chase the burglars away before they steal the valuables in the bank. That is like when a vaccine protects you from serious illness and death even though it doesn’t protect you from the initial infection. For viruses that won’t go away or that even change over time, boosters can upgrade the bank’s security measures. Boosters not only ensure the camera systems are up-to-date, but also provide the security guards inside the bank with new training and equipment so that they are prepared to repel any burglars. The camera systems providing outer-defense and the guards providing inner-defense may technically still be able to complete their responsibilities without boosters. However, since boosters typically contain updated Information about the virus’ new strengths and weaknesses, the security systems and trained guards who have to face the infection without boosters are at a disadvantage with fewer resources and less knowledge than those who received the vaccine booster.
Literal	To understand the reason for vaccinations, it’s important to understand how vaccines work. Vaccines enable your immune system to do two things: (1) stop you getting infected by viruses or, (2) if you do get infected, end the infection itself because of the help your immune system has had from the vaccine. One important factor in stopping infections is the presence of antibodies. If you have them in sufficient numbers, then you won’t get infected. But if you don’t have enough antibodies, the virus can start replicating in your cells and you get an infection. However, all is not lost. There are still your memory B and memory T cells. They can eliminate the infection in your body so that you recover without getting very sick. Vaccines enable your body to develop both the antibodies that help prevent infection and also the memory cells that can react to a potential infection. However, the antibodies decrease in number over time. As they decrease, the vaccine’s effectiveness wanes, and you may become infected even though you’ve been vaccinated. However, your memory B and T cells last much longer, and are always ready to deal with an infection. This is how a vaccine prevents serious illness and death even when it doesn’t prevent infection. For viruses that won’t go away or that even change over time, boosters can both increase the number of antibodies again as well as strengthen the memory cells in case they are needed.
Question 2: Is “natural immunity” better than the immunity provided by a vaccine?
Metaphor 1: Pilot	Vaccines help your body build up immunity safely without the risks associated with a viral infection. In this way, vaccines are like the flight simulation programs that airplane pilots are trained on before they attempt to fly a plane through bad weather conditions. This training allows pilots to practice flying through (simulated) bad weather in a safe environment, helping them become better pilots in real life later on. In the same way, vaccines help to train your immune system to handle a virus without the risks associated with a real infection. When an untrained pilot encounters bad weather for the first time while actually flying, they may be able to figure out how to get through it without crashing the plane, and having that experience would help them fly in bad weather better in the future. However, there’s always more risk of crashing when pilots have no prior training. Similarly, there is always more risk that a person can become very ill from an infection if they have no prior immunity. In other words, immunity can be achieved either by being infected with a virus or by being vaccinated against it. However, with vaccines there is little risk of serious illness in this process.
Metaphor 2: Fire Drill	Vaccines help your body build up immunity safely without the risks associated with a viral infection. In this way, vaccines are like the fire drills that students do in schools. These drills allow them to practice what they would do in a fire emergency but in a safe environment, so they would be better able to handle a real fire if one occurred. In the same way, vaccines help train your immune system to handle a virus without the risks associated with a real infection. If untrained students experience a fire in the classroom, they may be able to figure out how to get through it without getting injured, and this experience would help them survive a similar fire in the future. However, there’s always more risk of panicking and getting seriously hurt in fire situations without training. Similarly, there is always more risk that a person can become very ill from an infection if they have no prior immunity. In other words, immunity can be achieved either by being infected with a virus or by being vaccinated against it. However, with vaccines there is little risk of serious illness in this process.
Literal	Vaccines help your body build up immunity safely without the risks associated with a viral infection. If an unvaccinated person recovers from a viral infection, their immune system may be able to protect them from similar viruses in the future. However, there is always a risk that a person might become very ill from the actual infection because they have no prior immunity. In other words, immunity can be achieved either by being infected with a virus or by being vaccinated against it. However, with vaccines there is little risk of serious illness in this process.
Question 3: Are vaccines that are developed quickly safe?
Metaphor 1: Cake	Scientists are now able to develop vaccines much more quickly than in the past. Why is this? Think about a baker who sells personalized cakes with messages like ‘Happy 50th birthday, Taylor!’ or ‘Congratulations on your new job, Sam!’. The baker might wait until they receive an order, and only then start the baking process from scratch, mixing the necessary ingredients, baking the cake, letting it cool, making the icing, and finally adding the customer’s personalized message. But this is a slow process. For a much more efficient service, bakers can make a batch of cakes ahead of time, and when a customer comes into the shop, they can ice the personalized message onto the pre-made cake. In a shorter amount of time, the personalized cake Is ready. In the same way, today’s scientists do not start inventing vaccines from scratch when a new virus comes along. After many years of research and testing they have developed a vaccine-base, like a generic cake. When a new virus emerges, they quickly get the information they need to adapt the vaccine to the virus, which Is like adding messages on the cake. This new vaccine is immediately ready to be tested before being rolled out to the public.
Metaphor 2: Video Game	Scientists are now able to develop vaccines much more quickly than in the past. Why is this? Think about the companies that produce video games. Rather than creating a brand-new video game each time players ask for new features like storylines, characters, or gameplay modes, companies can meet their players’ wishes by releasing updates to pre-existing games that can be downloaded to players’ existing consoles. The developers simply write a piece of new code. They can then release game updates or patches that add these new features to their pre-existing video games, allowing players to continue playing their game with the latest features, all without needing to develop a brand-new game from scratch. These updates and patches with new game features are alterations to the original base program that can easily be tested and refined before finally being released to the public. In the same way, today’s scientists do not start inventing vaccines from scratch when a new virus comes along. They have already developed an existing vaccine-base after many years of research and testing. When a new virus emerges, they quickly get the information they need to adapt the vaccine to the virus, which is like updating their base with the necessary and latest features. This new vaccine is immediately ready to be tested before being rolled out to the public.
Literal	Scientists are now able to develop vaccines much more quickly than in the past. Why is this? Nowadays, scientists do not start inventing vaccines from scratch when a new virus comes along. After many years of research and testing, they have developed generic technologies and platforms that can be used and adapted to fit any virus. When a new virus emerges, scientists quickly get the information they need to adapt the generic platform and create a new vaccine that is immediately ready to be tested before being rolled out to the public.
Question 4: Why should I take a vaccine if I am personally low-risk for the illness?
Metaphor 1: Speed Limit	With certain viruses, some people who get infected experience only minor symptoms while others can get very sick or even die. When there is uncertainty with new viruses, however, everyone is invited to get vaccinated, regardless of their own personal risk level. Likewise, speed limits apply equally to all drivers and vehicles. Even though different vehicles have different safety features for occupants, it doesn’t make sense to allow some people to drive faster based on the safety features of their personal vehicle. This is because, even though some drivers might at lower risk of personal injury because of their vehicle’s safety features, those drivers would still be a danger to other drivers on the road. In the same way, unvaccinated low-risk people may be less likely to be harmed by a virus, but they are still a danger to people who are more likely to be made very ill by the virus.
Metaphor 2: War	With certain viruses, some people who get infected can experience minor symptoms while others can get very sick or even die. When there is uncertainty with new viruses, however, everyone is invited to get vaccinated, regardless of their own personal risk level. Likewise, when a country is attacked in war, its leaders mobilize people, weapons, and resources from throughout the different regions of the country to defend it. This is because, even though some regions are low-risk, meaning less vulnerable to attack than others, it wouldn’t make sense to exempt them from contributing, because cooperation across regions makes it more likely the country can repel the invaders. In the same way, unvaccinated low-risk people may be less likely to be harmed by a virus, but they can support the health of entire population by getting vaccinated, which helps the nation fight off the virus and reduces the chances of high-risk people becoming ill.
Literal	With certain viruses, some people who get infected experience minor symptoms while others can get very sick or even die. When there is uncertainty with new viruses, however, everyone is invited to get vaccinated, regardless of their own personal risk level. This is because, if low-risk people are unvaccinated, they may still infect other people who are more likely to be made very ill by the virus. So, unvaccinated people can be a danger to others, even if the chance of them becoming very ill is small.
Question 5: Why get a vaccine if it isn’t 100% effective?
Metaphor 1: Raincoat	Being vaccinated is an effective way of reducing your chances of being infected with a virus, just like wearing a waterproof raincoat during a storm reduces your chances of becoming wet. However, even the best raincoats don’t provide 100% protection from getting wet. In the same way, vaccines don’t provide 100% protection from a virus, and it is still possible to become sick even after you have been vaccinated and given a booster. For example, you could get sick if you are exposed to a large amount of the virus in your daily life, which is like going out during a severe rainstorm. You could also get sick if the immune reaction caused by the vaccine has not been strong or if a new variant develops that partly evades the vaccine. This is like a raincoat not fitting you well. Also, the effects of the vaccine might wane eventually, just like a raincoat might fray, develop holes, and wear out over time. For these reasons, when there are high infection rates in your area, it is still important to take additional precautions even after vaccination. These include avoiding crowded indoor spaces (as you would avoid severe rainstorms) and wearing a face mask (like using an umbrella even though you are also wearing a raincoat).
Metaphor 2: Seatbelt	Being vaccinated is an effective way of reducing your chances of being infected with a virus, just like wearing a seatbelt reduces your chances of getting injured in a car crash. However, even the best seatbelts don’t provide 100% protection from getting hurt. In the same way, vaccines don’t provide 100% protection from the virus, and it is still possible to become sick even after you have been vaccinated and given a booster. For example, you could get sick if you are exposed to a large amount of the virus in your daily life, which is like spending a lot of time in heavy, fast traffic. You could also get sick if the immune reaction caused by the vaccine has not been strong or if a new variant develops that partly evades the vaccine. This is like a seatbelt not fitting you well. Finally, the effects of the vaccine might wane eventually, just like a seatbelt might become less effective due to age and wear and tear. For these reasons, when there are high infection rates in your area, it is still important to take additional precautions even after vaccination. These include avoiding crowded indoor spaces (as you would avoid reckless driving) and wearing a face mask (like driving a car with airbags even though you are also wearing a seatbelt).
Literal	Being vaccinated is an effective way of reducing your chances of being infected with a virus. However, vaccines do not provide 100% protection, and it is still possible to become sick even after you have been vaccinated and had a booster. For example, you could get infected if were exposed to a large amount of a virus in your daily life. You could also get infected if the immune reaction caused by the vaccine has not been strong, or if a new variant develops that partly evades the vaccine. Finally, the effects of the vaccine might wane eventually. For these reasons, when there are high infection rates in your area, it is still important to take additional precautions even after vaccination, like avoiding crowded indoor spaces and wearing a face mask.