In short, vaccines work. They do what they are designed to do, which is to protect the recipient from certain diseases. So if you receive a vaccine for chickenpox, you are less likely to develop chickenpox if you are ever exposed to the disease in the future. And if a whole community receives the vaccine, the number of cases of chickenpox will decline in that community.
The proof that vaccines work is all around us. There have been fewer cases of chickenpox in the United States ever since that particular vaccine became commonly used. And there are fewer cases of measles, mumps, and rubella, fewer cases of polio, tetanus, and diphtheria, in the United States than there were fifty years ago. To use just one specific example, there were millions of cases of measles in the United States every year before 1950. Between
2000 and 2007, there were fewer than one hundred cases per year.
Some people argue that vaccines are not responsible for this rapid decrease in certain illnesses. Instead, they cite improved nutrition and sanitation in the United States as the reason for improved health and the corresponding drop in infectious diseases. While this is certainly part of the equation for some illnesses, such as hepatitis A, it is not the only explanation, and it is rarely the major contributing factor.
For other illnesses, improved sanitation and nutrition are clearly irrelevant. In 1985 there were over twenty thousand cases of severe Haemophilus influenzae type B (HiB) meningitis in the United States. In 1995, there were only one hundred cases. The HiB vaccine came into widespread use in the late 1980s. No one can argue that the United States had better nutrition or sanitation from 1985 to 1995. The logical conclusion is that the disease was almost wiped out in the United States by the vaccine.
Chickenpox is another example. Why would improved sanitation and nutrition wipe out measles and mumps and rubella but not chickenpox? In the 1950s there were millions of cases of these diseases. In the 1980s there were still millions of cases of chickenpox but only hundreds or at most thousands of cases of measles and mumps and rubella. The difference is that vaccines for measles, mumps, and rubella came out in the 1950s and 1960s, but the chickenpox vaccine didn’t come into widespread use until the 1990s.
This doesn’t mean that vaccines are unequivocally wonderful. You might still argue that the side effects are too risky or that a given vaccine is not cost effective or that a certain disease is so mild that we don’t need a vaccine. But people who say vaccines don’t work are simply wrong.
And in the end, you want them to be wrong; you want vaccines to work. Back in the 1950s, parents lived in fear of certain infectious diseases. They knew of a child who had been hospitalized with complications from measles; they knew someone paralyzed with polio or of a baby who had died of pertussis. They were desperate to protect their children from these illnesses.
Even today, you want vaccines to work. If you are going to be exposed to yellow fever in South America, a disease with a 50 percent fatality rate if you happen to contract it, you are glad that a vaccine exists. You want to be sure the vaccine works as best as it possibly can.