Often, we as humans like to reminisce about simpler times. We tend to remember less complicated lives filled with picnics and field games and comfort food. Perhaps it helps us deal with the stress of overscheduled lives and far-flung families. Whatever the reason, the pull toward memory lane is a constant across the decades.

But in this activity, we often resort to revisionist history to make sure the memories support our need to visualize a simpler time. As such, we delete some of the less picturesque images, including pestilence and disease that resulted from a simpler scientific time when we did not have vaccines or medications.

To remember pre-vaccination eras really does not take much. The U.S. mumps vaccination program only began in 1967. Around 186,000 cases were reported during that time, probably only a percentage of true illness. Deafness, sterility, encephalitis and death were known to occur occasionally. In the next few decades, the disease decreased by 99 percent concomitant with the widespread use of the vaccine.

However, we are again starting to see the resurgence of vaccine-preventable diseases. In 2016, 46 states reported mumps cases, with seven states reporting over 100 cases apiece. In fact, in the last decade there have been multiple outbreaks of mumps, several concentrated over the Midwest. And while complications are rare, they do occur as they did when the disease was rampant. Even uncomplicated cases can last a couple of weeks resulting in significant loss of school and work time.

[See: Top Reasons Kids End Up in the Hospital.]

So why do we continue seeing outbreaks of vaccine-preventable diseases? There are actually a few reasons that measles, mumps, chicken pox and others continue to appear even in the vaccine era.

First, the vaccines are not 100 percent effective. Of course, nothing in medicine is 100 percent in any category. So how effective is “effective enough”? The MMR vaccine, which includes protection against mumps, is approximately 85 percent effective after two doses. Even if vaccines don’t work 25 to 30 percent of the time, there are still hundreds of thousands of people who are protected. If we were discussing the lottery, clearly an 85 percent chance of winning would be big incentive to buy a ticket. Vaccines, which were really the first (and so far best) foray of the medical system into population health, are extremely effective. Statistics from the Centers for Disease Control and Prevention show that for Americans born between 1994 and 2013, vaccines have prevented 322 million illnesses, 21 million hospital admissions and 732,000 deaths. Herd immunity, or enough effectiveness in the population to prevent large outbreaks, can be achieved with the efficacy of current vaccines.

The other main reason we continue to see outbreaks is due to vaccine hesitancy. This represents a growing subset of caregivers who have concerns about immunizing their children. Some do not want vaccines at all. The most common reason cited is fear about vaccine safety. This is somewhat surprising in light of the mountains of evidence confirming the safety of vaccinations. While minor reactions occur (like redness and tenderness at the injection site, fever and occasional rashes), they are short-lived and, except for transient discomfort, have no significant health effects.

[See: 10 Concerns Parents Have About Their Kids’ Health.]

Life-threatening reactions, like a true allergic reaction, occur in fewer than 1 in 1 million vaccinations. That risk is smaller than getting one of these diseases, even in the modern era, where they are much more rare. There is overwhelming support regarding vaccine safety. Each vaccine is put through a rigorous four-phase safety and efficacy evaluation over the 10 to 15 years it takes to actually get one to the market.

The other group included in the vaccine-hesitant set are those who opt to only give some vaccines or give them on a very drawn-out schedule. The reasoning here is that people are concerned that the immune system of a young child could be overwhelmed. However, the fact is: The immune system is developed by being stimulated. By seeing illnesses or vaccine components, the body can make antibodies to protect against the germ when seen again. Immunity builds over time and exposure.

Vaccines either contain killed components that stimulate immune response (but aren’t capable of causing illness) or they are “live but attenuated,” meaning they are diluted out so that they can stimulate the immune response but not cause the illness. There is no evidence that there is a max on how much the immune system can process at any given time.

The vaccine schedule has been very thoughtfully considered and intentional in its recommendations. It tries to minimize the number of sticks, and only include illnesses that can spread quickly and have serious consequences; it strives to maximize the protection of all. Delaying shots, spreading them out too far or foregoing any particular one results in under-protection of the most vulnerable: our youngest babies and children. In a recent survey, pediatricians reported that only about 1 in 3 families opt to follow the recommended vaccine schedule.

[See: 9 Ways to Boost Your Immune System.]

The vaccine debate continues to gather steam in this country, with more polarizing positions being observed. Approximately 11 percent of pediatricians now report taking a hard stance on dismissing patients who do not opt for vaccination, a figure that has nearly doubled in the last seven years. Social media campaigns by the thousands are posted every week extolling either the virtues or the pitfalls of vaccines. It can be very hard to discern the proper course.

In that case we should always look to the science and weigh the evidence. One constant: When vaccination rates go down, diseases go up, no matter how rare any particular disease has been in modern times. We cannot eradicate most germs, they are always lurking. If there is anything to ponder, it is not the science. That is very clear.

Perhaps we should instead consider how we would feel if we were standing at the bedside of a very sick child knowing we could have prevented his or her discomfort, pain and suffering with a few seconds of a shot. That’s not a picture any of us wants for a later trip down memory lane. Be proactive, take steps to control your child’s health. Don’t hesitate — vaccinate!

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Vaccines Are Safe and Necessary originally appeared on usnews.com