We all know that we get vaccinated to protect against disease. But even vaccinated people can sometimes get sick with the disease they are supposed to be protected against. That's particularly true for pertussis (whooping cough). You may have heard lately about the rise in cases of pertussis—and how both unvaccinated and vaccinated individuals are getting sick from it. Maybe you are wondering why we don't have a better vaccine for this dangerous illness, or why more pertussis cases are occurring among vaccinated people than in the past.
There are three main reasons why the current pertussis vaccine isn't as effective as we would like:
1. A good vaccine is hard to make.
Vaccines work by stimulating the immune system to create a sort of "memory" of a pathogen so that it can subsequently recognize and and attack that pathogen before it can cause illness. One of the most effective ways to do that is by using the whole, killed pathogen (in the case of pertussis, a bacterium) in the vaccine. The original pertussis vaccine developed back in the 1940s was just this type of "whole cell" vaccine, and it was highly effective. Unfortunately, it also caused an an undesirably high rate of side effects. As a result, since the 1990s most of us have gotten a newer, "acellular" pertussis vaccine that's made from purified components of the pertussis bacteria rather than the entire bacteria.
The acellular vaccine causes fewer side effects, but it protects against disease less effectively and for a shorter time than the whole cell vaccine did. There is also evidence that the acellular vaccine may allow you to get infected with pertussis, though it will prevent you from getting sick. What this means is that you won't have symptoms of pertussis but may still be infected and able to pass the disease along to others.By allowing more people to unknowingly carry the bacterium, the vaccine permits more exposure to pertussis, which under the right circumstances can lead to more disease, even in areas with high vaccination rates.
2. Pertussis immunity wanes over time.
Neither the old nor the new pertussis vaccine confers lifelong immunity. That's why we have to get multiple doses of pertussis vaccine over our lifetime. Vaccinated individuals gradually lose antibodies againstpertussis, which means that they ultimately are at risk for infection and passing that infection on to others (though vaccinated people who do get sick are likely to have milder illness than people who haven’t been vaccinated).
3. More parents are refusing to vaccinate their children.
In order for a vaccine to be effective, particularly one that induces a shorter period of immunity than others, the whole society needs to be vaccinated. This keeps infection from spreading. Pertussisis one of the best examples of how herd immunity can protect the very young and vulnerable members of society. Adults who get sick with pertussis often do not experience severe illness, but can pass it easily to children around them. Very young children are the population at greatest risk for developing life-threatening disease—so getting young infants vaccinated as early as allowed has a significant impact on reducing deaths and complications from pertussis.
Bottom line: An imperfect pertussis vaccine is far preferable to no vaccine. To protect yourself—and the vulnerable people around you, particularly young children—make sure that you and your family members are vaccinated according to the CDC's recommended schedule.