What we know now is that DPT (diphtheria, pertussis and tetanus) vaccine that was introduced in the late-1940s in [the United States] and used on a mass basis and the DTaP vaccine that replaced DPT in the late-1990s, neither of those vaccines could prevent [pertussis) infection and transmission of infection by vaccinated persons. What you have is a lot of people who have been vaccinated who have mild symptoms or are asymptomatic, no symptoms at all, who can become infected and transmit to both vaccinated and unvaccinated people.

So it’s an illusion that there is vaccine-acquired herd immunity. And it’s always been an illusion, because the [pertussis] microbe has responded to mass vaccination and has evolved, created strains that are not covered in the vaccine. The other thing is that vaccine-acquired immunity is extremely temporary, if at all… perhaps less than two years.

So you have a lot of pertussis in our country, but it’s not being identified and it’s not being reported. You’re seeing a rise in pertussis reports now because cases that are symptomatic are being diagnosed. But you cannot say that pertussis vaccine is preventing pertussis in this country and, therefore, you cannot claim that there is herd immunity from pertussis vaccine.

— Barbara Loe Fisher, co-founder and president of the National Vaccine Information Center (NVIC)