“Are vaccines safe?” is a question that we get asked regularly. My first response is, “Are vaccines safer than what?” Safety is a relative concept; absolutely nothing in life is completely risk-free. For instance, over the last twenty years, consistently every year, 1 in 6,000 Americans will die in an automobile accident, a far higher risk than anyone has even suggested for any vaccine. Yet we still ride in cars, because the benefit justifies the risk. So with any particular vaccine, the question is, “Is it safer to get the vaccine, or not to get the vaccine?” There are really two questions whose answers must be considered:

1. What bad things can happen due to getting a particular vaccine?
2. What bad things can happen due to not getting that same vaccine?

Sometimes parents hear about something bad that happened to someone else’s child and want to avoid that same situation for their own child. The problem is figuring out whether a particular exposure caused a particular result. “My son ate a bologna sandwich, and then climbed a tree and then fell out,” doesn’t mean that bologna increases the risk of falling out of a tree. That makes sense to parents because they understand bologna, and they understand how children fall out of trees, so they can be confident that the two are not connected.

But if some other parent was convinced that bologna caused falls, how could you convince her to change her mind? You might look at 1000 children who ate bologna, and 1000 children who didn’t eat bologna, and show that those who didn’t eat bologna were just as likely to fall out of trees as those who did eat bologna.

The same basic principle holds with vaccines. For instance, some children who got a Measles-Mumps-Rubella (MMR) vaccine were later diagnosed with autism. But that alone doesn’t tell us whether the vaccine caused the autism. If you substitute “ate a bologna sandwich” with “got an MMR vaccine” and substitute “fell out of a tree” with “was diagnosed with autism” you can look at 1000 children who got the MMR vaccine to see if they had more autism than some group of 1000 children who didn’t get the MMR vaccine. That should give you a pretty good answer of whether the MMR vaccine really caused the autism, or if it was more like the bologna and the tree, two events that really happened to the same child, without one causing the other.

No. People wondered about MMR and autism because the first MMR vaccine is given at 12 months of age, and the signs of autism are often not noticed until they become more obvious around 15 to 18 months of age. But as with the bologna and the tree discussed above, we don’t just want to know the timing. We want to know the comparative risk.

In 1998, a British doctor published research that connected MMR vaccination to autism. But his results were not duplicated by other doctors who studied the same thing, and it turned out that he had a conflict of interest; he was being paid by a lawyer who was trying to make money off of MMR lawsuits.

Even so, due to public interest, further research was done to answer the question of whether children receiving MMR vaccination were more likely to develop autism. Several studies did this with large groups of children, even one involving 600,000 children. They all agreed: Autism is not more common in children who receive MMR than in children who don’t.

The research connecting a mercury-based preservative (thimerasol) to autism was weak in the first place. But because of bad publicity, in 2001 thimerasol was removed from all the vaccines that babies get. It hasn’t made any difference in the rate of autism. Also, mercury is everywhere, in tiny, tiny doses. During the first 18 months of life a breast fed baby consumes six times the mercury that used to be in all the vaccines given in that same time period. Mercury is in fish and other foods. In higher doses, it could be a problem. But in the doses we encounter it, there’s just not enough to worry about.

Unfortunately, the scare over the false connection between MMR and autism caused some parents to refuse to vaccinate their children, and as a result, we’ve seen an increase in outbreaks of measles, mumps, and rubella. This is because no vaccine is perfect; doctors aim for a vaccine to be 95% effective. This means that 5% of vaccinated children are still not protected. In vaccinated areas of the USA, there may be one case of measles every couple of years. But in May 2008, Pima County, Arizona had a measles outbreak with 21 cases between February and May. Outbreaks like this are becoming more common in areas that don’t keep up with vaccination.

Before the vaccine, America experienced 500,000 cases of measles annually. 150,000 of those developed pneumonia or croup, 48,000 required hospitalization, 7,000 had seizures, 4,000 developed encephalitis (brain infection), and 1,000 had permanent brain damage or deafness. Similarly, mumps can cause male infertility and encephalitis, and rubella can cause severe brain damage to unborn babies whose mothers contract the disease.

A 1977 study in New Zealand showed that out of 23 unvaccinated children, none had asthma 5-10 years later, compared to % of the 1184 vaccinated children. 23 is a pretty small number for a medical trial to reach a conclusion, but it was interesting enough to warrant further study. So another study was done of 167,240 children in America. It found no increase in the risk of asthma after DTP vaccination.

Most people know that Tetanus causes “lockjaw,” muscle spasms associated with difficulty swallowing and breathing which lasts for weeks. It kills 11% of those who get it. Diphtheria is a respiratory disease which can cause swelling of the neck and heart problems. It kills 5-10% of its victims overall, but up to 20% of young children. Pertussis causes a severe cough which lasts for months. For instance, despite modern medicine, pertussis killed 17 babies in the USA in 2001.

It’s true that most healthy people who get influenza get over it (after about a week of feeling terrible. But every year, healthy American children die of influenza.

Recently one child with a very rare mitochondrial disease developed autism soon after receiving vaccination. Research is ongoing to determine whether vaccines can increase the risk of autism in this sort of child. We don’t routinely test all children for mitochondrial disease because it’s quite expensive, involving much blood sampling and even muscle biopsy. Even if there is a tiny group of children for whom vaccines are unsafe, the odds still favor vaccination, because the likelihood of vaccine-preventable illness is higher than the likelihood of mitochondrial disease.

It’s not required for homeschooled children to receive vaccines. That doesn’t make it wise to refuse vaccination. The state doesn’t forbid your children to roll around in poison ivy, but you still wouldn’t let them do it, because it’s not in their best interest. The goal is not to do the least allowed by the law. The goal is to do what’s most helpful and safest for your children.

If everyone else gets the vaccine, yes. But it’s not fair to ask everyone else to shoulder the burden of vaccination just so your family can be safe. We owe it to our neighbors to protect them and their families, as well as our own. Do to others as you would like them to do to you.