Vaccines and 1957?!

Q. What is the significance of the year 1957 with reference to vaccinations? It keeps coming up!

A: This is a very interesting question; and I had to do a bit of reading to be able to write a decent answer. This applies specifically to MMR (measles, mumps and rubella) vaccination in the United States.

The schedule for adult vaccination in the US is as follows, which shows that the MMR vaccine is to be given to non-immunised adults born in 1957 or later.

Figure 1: Schedule for adult immunization in the US. Source: cdc.gov

Of course, public health policies are rarely arbitrary, and the cut-off of 1957 has to do with the development of vaccines for measles, mumps and rubella.

The Development of Vaccines for Measles, Mumps and Rubella

The following graph shows the annual incidence of measles in the United States from 1944 to 2007. From 1944 to the mid-1960s, large measles epidemics typically occurred every few years, superimposed on a generally high incidence – which causes the jagged appearance of the graph. However, after 1964, the graph tells us a different picture – a dramatic fall in the incidence of measles after the introduction of the vaccine.

Figure 2: Annual incidence of measles in the United States from 1944 to 2007. Data from CDC, Atlanta.

As the number of new measles cases was perceptibly much lower after the introduction of the vaccine, immunising children against measles became a standard practice.

Shortly thereafter, the mumps vaccine was introduced in 1967 and the rubella vaccine in 1970. In 1971, an American microbiologist named Maurice Hilleman developed a combined vaccine for all three diseases containing attenuated strains of all three viruses. This vaccine effectively replaced the existing individual vaccines, and mumps and rubella also showed similarly drastic reduction in annual incidence rates.

Because these diseases were tremendously common in the US (and the rest of the world) before the introduction of these vaccines, almost every child by the age of 6-7 in endemic areas would have contracted them. And because first-time infection with one of these viruses would confer lifelong immunity, those children would be immune to developing those specific diseases after the first instance of infection.

Because every public health programme has its costs, and because the law of diminishing returns dictates that there is a point beyond which the benefits gained from a particular practice are progressively lesser than the amount of money or energy invested in the practice, it was thought that vaccinating people who had already contracted the disease in the past would not be the most effective utilisation of resources. Since almost every individual aged 6 or above before the introduction of these vaccines was believed to have already developed these diseases at some point, it was decided that immunising only those born in 1957 or later (who would be roughly 6, 10 and 13 years old at the times of introduction of vaccines for measles, mumps and rubella respectively) would be optimal, and that is why US recommendations don’t recommend MMR vaccines for adults born before 1957.

Dr Anmol Dhawan

References

1. Centers for Disease Control and Prevention. Recommended Immunization Schedule for Adults Aged 19 Years or Older, United States, 2018 https://www.cdc.gov/vaccines/schedules/hcp/imz/adult-shell.html
2. Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, McIntyre L, eds. 11th ed. Washington DC: Public Health Foundation, 2009