A new study released includes a mathematical model that tests the effectiveness of vaccines could also explain why certain diseases can re-emerge despite high vaccination rates. Vaccines work by provoking a response from a person’s immune system similar to when someone is infected except that it doesn’t cause someone to contract the actual diseases.

There are times when vaccines fail or can actually result in an infection. However, for the vast majority of people, vaccines do prevent the spread of disease through herd immunity. What puzzled doctors for years was why at times diseases would emerge among an infected population. Researchers for the study used different scenarios and models while taking into account infected populations, population age, recovery rates and different types of vaccines used. Scientists concluded that diseases return among vaccinated populations it is due to a leaky vaccine effect.

A leaky vaccine reduces, but does not eliminate, the chances of infection when a population is exposed to a disease. If vaccination rates are not at critical ratio levels, then the chances of an outbreak increase. A critical ratio level is based on how many individuals have to be vaccinated in a given population in order for a disease to be eliminated. The disease in question results in a kind of honeymoon effect. If a population that experienced an outbreak of measles and is also not fully vaccinated then at some point becomes fully vaccinated, the disease can re-emerge some years or even decades later.

If vaccination coverage is maintained below [the critical ratio] then the disease is not eliminated and the purely leaky vaccine would result in the highest level of infection in the long run, study author and post doctorate fellow Elicia Magpantay said.

This not only explains why diseases re-emerge years later when thought to have been eradicated but also answer anti-vaccine groups charge that vaccines either don’t work or people get infected resulting from vaccinations. There are rare instances when people’s bodies react to a vaccine where they become infected. John Salamone’s son, David, was infected with polio but after his lobbying the medical community convinced them to use the injected, rather than the oral, vaccine that resulted in Salamone’s son becoming infected with polio.

I have no doubt the information in this study will not be effective enough to blunt the charges of anti-vaccine groups who have charged that vaccines infect people with disease. Despite their claims, anti-vaccine groups do not want better vaccines, they don’t want any at all.