All FDA-approved vaccines must undergo extensive laboratory testing and then rigorous clinical trials that must demonstrate both safety and efficacy. Further, epidemiological data provide real-world evidence that overwhelmingly supports a major role for vaccinations in the robust and long-lasting health enjoyed by those living in developed nations - a degree of disease-free survival that is unprecedented in human history.

As quoted in our guest column (CHN May 22), a number of horrific diseases that once were endemic have become rare directly following the development and administration of vaccination. Polio has been eradicated from our hemisphere. There are now no cases of congenital rubella in the U.S., and small pox exists only in test tubes under guard. It is irrefutable that vaccines have resulted in dramatic decreases in measles, mumps, rubella, and whooping cough, saving the lives of millions of children worldwide.

This is not to say that vaccines, like most all medical procedures and medications, do not, sometimes, have serious side effects. Advocates for vaccination are not blind to these adverse events. However, the balance between risk and benefit weighs heavily in favor of vaccination. Importantly, associations between certain vaccinations and autism have been debunked.

Yang Shulian mentions a study correlating vaccination doses and infant mortality and may be referring to a recently published analysis comparing rates of infant death and national vaccine recommendations. However, that certain events seem to occur together does not mean that one causes the other. For example, an illness is not caused by a fever, although they are tightly associated. Similarly, this study suffers from a number of biases in attempting to explain differences in infant mortality across nations using the single variable of vaccination.

In fact, it is the absence of vaccination that has been repeatedly demonstrated to cause actual harm. In Marin and Sonoma counties in California, local rates of personal-belief exemptions to childhood vaccinations are the highest in the state, and so too was the rate of whooping cough last year. Outbreaks of whooping cough have hit closer to home, in Durham, leading to renewed efforts to encourage vaccination here.

There is a history of tension between advocates for vaccination and advocates for civil liberty, deftly chronicled by Michael Willrich in his book, "Pox: An American History." Unfortunately this legacy continues to contribute to suspicion regarding vaccines. Willrich, as well as Yang Shulian's reaction, make a strong case for health officials to acknowledge and better address a public mistrust of vaccines, and dispel vaccine myths so that these potent, effective, and, yes, relatively very safe, tools to prevent disease can be more readily accepted.