Many people don't remember the time before vaccines. The Children's Hospital of Philadelphia describes it as a world when parents kept their children out of public swimming pools to prevent polio and held "chicken pox parties," in hopes their children would get milder cases when they were young.

Vaccines have made history of many diseases, but challenges remain.

This year, the National Advisory Committee on Immunization Practices has recommended not using the live nasal spray influenza vaccine for the 2016-2017 flu season.

Paul Offit, director of the Vaccine Education Center at CHOP, recently spoke to us about that recommendation and other vaccine issues, including why so many parents are reluctant to give their kids shots that prevent certain cancers. (CHOP has parent resources at http://www.chop.edu/centers-programs/parents-pack.)

What's behind the ACIP decision on the nasal spray vaccine?
FluMist has been used for a number of years. But the last three years, the efficacy of FluMist has been worse. The shot has worked better. In fact, last year, the nasal spray had only about a 3 percent efficacy rate, which is woeful. For that reason, the ACIP withdrew its recommendation to give FluMist for the upcoming season.

About 8 percent of the U.S. flu vaccine market is Flu-Mist, but it's 33 percent of the pediatric market. Many children prefer the nasal spray because the shot obviously hurts more. What's worrisome is that with this recommendation, you can assume there will be children who won't get any flu vaccine this year because they can't get the FluMist.

The vaccine is important because influenza causes a couple hundred thousand people to be hospitalized every year. It causes between 20,000 and 35,000 deaths every year, including 75 to 150 children.

It might take two years - that's my guess - but I think the Flu-Mist problem is solvable.

What's the latest on the vaccine for human papillomavirus (HPV)?
It's been available for 10 years. It's recommended for all adolescents, ages 11 to 13, boys and girls. Yet only about 40 percent of girls and 15 percent of boys receive this cancer-preventing vaccine.

One reason is that the virus is only transmitted by sexual contact, and I think it's been difficult for clinicians to talk about that with parents and with young children, before they've had sex. My feeling is they don't have to talk about sex. Just talk about the fact that this is a cancer-preventing vaccine. It's a preventative vaccine only, not a therapeutic vaccine, so it won't work after you've been infected. Therefore, you need to get it before you've had sex. Hence, giving it to young adolescents.

There are also vague notions in the general public that the vaccine might be unsafe, when in fact that's been clearly shown not to be true. This vaccine was tested for seven years in 30,000 people before it was licensed. And it's been tested since licensure in more than a million people, formally. It is the most-studied vaccine for safety.

There's also the notion that this would promote promiscuity. By the same logic, you might fear that giving a tetanus vaccine would cause children to walk over beds of rusty nails with impunity. The HPV vaccine doesn't provide absolute protection. It doesn't prevent all HPV strains, just the most common ones. And HPV is not the only sexually transmitted disease; gonorrhea, syphilis, and chlamydia are also sexually transmitted. So the notion that the HPV vaccine means that you are protected against all sexually transmitted diseases is a false one.

But the current vaccine will prevent about 29,000 cases of cancer every year, and about 5,000 deaths a year. That's what this vaccine will do. But because only 40 percent of girls and 15 percent of boys get it, you can assume about 2,000 children a year will grow up and die because they haven't gotten this vaccine. It's unconscionable. Frankly, it shouldn't be an option to not get it. Parents should not be given a choice to put their children at this kind of unnecessary risk.

In general, are enough children being vaccinated?
The Centers for Disease Control and Prevention estimates that 2 percent of parents are not vaccinating their children at all, and 10 to 20 percent are delaying or not getting the vaccines according to the routine schedule.

It's beyond worrisome. We've already seen the effect of that. In 2014, in an Amish community in Ohio, about 680 people got measles. In 2015, a measles outbreak started in Disneyland and spread to 25 states, involving 189 people. It also spread into two Canadian provinces, where it involved hundreds more people. We had basically eliminated measles in the U.S. by the year 2000. But when enough people choose not to vaccinate, the disease comes back.

Why aren't people vaccinating their children?
Vaccines have been a victim of their own success. I think we have to re-explain ourselves. You certainly didn't have to convince my parents that vaccines were important. They saw diphtheria as a common illness. They saw polio as a crippler of children. Same with me: I had measles, mumps, chicken pox. I knew how miserable those diseases made me.

But today's young parents don't see these diseases we're preventing. Their children are getting 26 inoculations in their first few years of life. And that can mean as many as five shots at one time to prevent diseases that most people don't see, using biological fluids that most people don't understand. So, it's not surprising that there's pushback.

All the vaccines that children currently receive are still important. You could argue, why get a polio vaccine? Why a diphtheria vaccine? Those diseases don't exist in this country. But the fact is that they exist in the world. If you choose to let your guard down, they will be back.

Are any promising new vaccines in the pipeline?
Two vaccines are recommended for pregnant women - the flu and whooping cough - to protect not only the women, but also their unborn children. That platform - the pregnancy platform - is the next great platform. For example, I'd like to see a vaccine for pregnant women against group B strep, a bacterial infection that still infects babies; some die. A vaccine for meningococcal disease could also be used during pregnancy to prevent disease in the first few months of life. And respiratory syncytial virus (RSV) is a common cause of pneumonia in young babies. These are diseases that can affect babies less than 6 months old - a baby that's too young to get that vaccine. But you immunize the mother, she has an antibody response, and she passes it on to the baby.