(This is the second in a four-part series. If you are just joining us, you might want to start with the introduction.)
Measles is a highly contagious virus transmitted like the common cold i.e. via respiratory droplets. It is so contagious that you can catch measles by entering a room that a contagious person had left two hours before. Most of the time, the illness is fairly mild. But rare infections can be severe and even fatal—and it is not simple to predict who will have it easy and who will really suffer. Since 1995, there has been an average of one measles-related death per year in the U.S. Young children and adults are at the highest risk for serious complications. This is part of why vaccination is scheduled to start early: to protect the most vulnerable. However, measles is not one of the earliest vaccines recommended by the CDC schedule, because it is not as effective when given before 12 months of age.
Some anti-vaccine activists say that improved sanitation and nutrition took care of infectious disease before the vaccines came around. Clean water and sewers certainly did impact the incidence of infectious disease. Regarding measles specifically, improved nutrition was a major factor in dropping the death rate (more so than the incidence of disease). This link shows rates of both disease and death in Britain; notice the big drop in deaths from measles well before the introduction of the vaccine in the 1960s. However, by mid-century, the rates had basically plateaued. Then the vaccine was introduced and drastically dropped the incidence of disease, and consequently deaths as well. From the CDC’s Pink Book:
“Before 1963 approximately 500,000 cases and 500 deaths were reported annually, with epidemic cycles every 2–3 years. However, the actual number of cases was estimated at 3–4 million annually. Following licensure of vaccine in 1963, the incidence of measles decreased by more than 98%, and 2–3-year epidemic cycles no longer occurred.”
Keep in mind, there are other complications from measles infection besides death. For more detail the history of measles and the measles vaccine, you might read Dr. Ian York’s interesting “Measles week” series.
While we are on the topic of sanitation, I’d like to mention that every intervention carries some risk. Do you remember when walking down a city street meant risking a pot of raw sewage being dumped on your head? Neither do I. While I have no interest in going back, I want to point out that even sanitation is a double-edged sword. Before clean water and sewers were commonplace, polio was endemic, meaning always present in some part of the population. However, infection in infants less than 6 months was rare and/or they were asymptomatic. After sanitation measures were rolled out, kids were not exposed to polio at such a young age, leading to decreased immunity and subsequently the polio epidemics of the 1940s and 1950s.
All right, so that is some background on measles itself. Let’s talk about the vaccine. MMRII is an effective vaccine. One dose works in 95-98% of kids, increasing to more than 99% after the booster dose. It is a live-virus vaccine that produces a mild, usually asymptomatic, non-communicable infection. Vaccine-induced immunity appears to be long-term and probably lifelong.
Vaccination may have had an impact on measles immunity and susceptibility in infants as well, even though children do not receive the vaccine until they are 12-15 months of age. Here is how that works: mothers, who develop a measles infection, develop a robust immune response. These antibodies are passed on to their infants and protect the babies in their first months of life. In moms who were vaccinated, fewer antibodies against measles cross the placenta to baby. This results in infants who are susceptible at a younger age than in the past. This is certainly a downside of immunization. The up side is that more of these babies survive to become parents than in days when wild-type measles was common.
I’ll get into the safety of the measles vaccine in the next installment. In the meantime, feel free to post questions you may have on my facebook page.