Measles: A Tale of Two Nations
Post #1197
In the USA, measles deaths dropped by 95% prior to the introduction of the measles vaccine in 1963:
The deaths in the top half of the graph undulate (go up, and then down, and then up again) for reasons not fully understood. After contrasting the undulation of measles deaths with that of England & Wales below, a hypothesis will be formed. Notice how cases (bottom half) remained high prior to the 1963 measles vaccine.
Here are 15-year jumps in cases, deaths, and case fatality for the USA:
Cases (USA)
In the center of the chart would be “1963” — when the measle vaccine came out.
Deaths (USA)
While deaths stayed low after 1985, the case fatality rate is made more vulnerable to wild swings (when, due to small numbers of cases, just one just one death makes it jump). This phenomenon shows up in the case fatality rate at right in the chart below.
Case Fatality (USA)
To get an indication of the drop during the 30 years from 1925 to 1955, here are these case fatality rates as a proportion of the 1925 rate:
At a value of 0.06 in 1955, the case fatality rate had dropped by 94% in the 30 years from 1925. Explaining that drop is important, and possibilities include nutrition, hygiene, and the maternal transfer of immune system antibodies to infants. Now let’s look at England & Wales:
Cases (UK)
Notice how the up-down undulation is almost completely uniform, down one year, up the next, down the next, and so on. This “annual alternation” — i.e., having “on” years with higher case counts, followed by “off” years with lower case counts — was not the case in the USA, however.
Deaths (UK)
After the USA got a measles vaccine (orange line), England & Wales did not get one for another 5 years (green line), and it almost looks like the vaccine in the USA “harmed” the measles cases in England & Wales (deaths ticked up there, once the USA got its vaccine). But this is pure speculation, and we need case fatality to answer it.
Notice how deaths also dropped by 95% prior to the measles vaccine (like in the USA).
Case Fatality (UK)
Oops! I must have “over-speculated” — by finding patterns in data which might actually be meaningless. Though cases in “off” years in England & Wales were rising after the USA got measles shots, the case fatality in England & Wales did not appreciably rise once the USA got its measles shots. Wild swings show up at right.
Hypothesis about the different patterns
But what explains the difference in undulation? How come England & Wales got substantial “outbreaks” every second year, like clockwork, but the USA did not?
One hypothesis is that, in England & Wales, maternal passing of immunity to infant made up most (~70%) of the measles immunity, but in the USA, it was mostly (~70%) nutrition. Here is a study showing how naturally-infected mothers gave protection to their infants for 12 months, even though vaccinated mothers only gave 6 months worth:
The authors explained that top right bold (unvaccinated mother) dot as an active measles infection, instead of being some kind of “super-immunity” from an unvaccinated mother which had miraculously beat out all other values — even though a year had already passed.
The protection from unvaccinated mothers lasted twice as long, before dipping below the antibody titre of 4.0. This “year of protection” would explain the undulation in England & Wales, because one-year olds would be catching measles after having been protected for their entire first year.
Critics and detractors may come back saying that it shouldn’t matter, because mothers have their babies at all different times and the protection levels should reach a steady-state when birth times are super-imposed on one another. But that reasoning suffers from the same mistake: it assumes all women have kids roughly equally.
Instead of each woman having had 2.5 kids back then, the reality was that one of them had 5 kids and the other had none — and the one who has 5 kids has them spaced apart, by about a year or two. It’s not great justification, but we’re just forming hypotheses here, and hypothesis-formation is not a perfect science, so cut me some slack.
Reference
[measles cases and deaths in the USA] — https://ourworldindata.org/grapher/measles-cases-and-death
[measles cases and deaths in England & Wales] — https://www.gov.uk/government/publications/measles-deaths-by-age-group-from-1980-to-2013-ons-data/measles-notifications-and-deaths-in-england-and-wales-1940-to-2013
[maternally-derived measles immunity] — Jenks PJ, Caul EO, Roome AP. Maternally derived measles immunity in children of naturally infected and vaccinated mothers. Epidemiol Infect. 1988 Oct;101(2):473-6. doi: 10.1017/s095026880005442x. PMID: 3053223; PMCID: PMC2249400. https://pmc.ncbi.nlm.nih.gov/articles/PMC2249400/pdf/epidinfect00011-0263.pdf