Measles is one of the world's most contagious viral infection of the respiratory system. A Princeton
University-led research has suggested that measles can spread more
quickly in schools than previously thought.
The researchers report in the journal Proceedings of the National Academy of Sciences
that the only sure method of controlling measles among schoolchildren is to maintain very high vaccination rates.
‘Measles can spread more quickly in schools than previously thought, suggested a new study.’
The researchers conducted one of the first direct examinations of
how measles spreads at the school level by reviewing data from a 1904
measles outbreak in London that affected 18 schools.
"While schools are
known hotspots for infections such as measles, scientists actually have
little information about the specific rate at which the measles spreads
among children in school," explained senior author Bryan Grenfell,
Princeton's Kathryn Briger and Sarah Fenton Professor of Ecology and
Evolutionary Biology and Public Affairs.
The data came from the Wellcome
Library's Collection of digitized historical medical documents
maintained by the London-based Wellcome Trust.
"This study addresses that gap with historical data," Grenfell said.
"We need to be cautious in comparing historical data from the early
1900s to transmission today; however, our study does illustrate the
potentially high transmission rates of infection in schools where
vaccination is low."
First author Alexander Becker, a Princeton graduate student of
ecology and evolutionary biology, said, "our direct estimates of measles
infection in schools indicate potentially swift transmission rates and a
consequent need to maintain vaccination levels."
A pathogen's infection rate is indicated by the figure R0 -
pronounced "R nought" - which indicates how many people catch a disease
from the initial carrier in a fully susceptible population, Becker
said. In the general population, measles has a notably high transmission
rate of R0 = 12-18.
In the schools at the center of the 1904 outbreak, the researchers
found that at the school level each sick child transmitted measles to an
average 27 people with the transmission rate at individual schools
falling within a range of 12 to 42. Zooming in to the classroom level,
each sick child infected 40 others on average with a transmission-rate
range as low as 8 in one school to a whopping 93 in another.
Using these historic estimates, the researchers investigated how
measles might spread in today's schools. There are presumably notable
differences in the living conditions, hygiene and crowding children
experienced in London in 1900 versus what children experience in the
21st-century United States, Becker said. Nonetheless, transmission
estimates from more recent periods in the pre-vaccination era indicate
that measles infection has been quite strongly focused in schools.
The researchers developed a mathematical model based on current
vaccination estimates in California and found that high vaccination
levels were required to prevent transmission.
"This work adds more evidence to the benefit of having a fully
vaccinated school-age population," Becker said. "Even if a school has
high coverage, it should push to go higher because there could be a risk
of a significant outbreak."
At the same time, Grenfell said, the study emphasizes that the
pervasiveness of measles once it infects a school population calls out
for a better understanding of how it spreads than scientists currently
"Probably the most recently studied infection at the school level is
influenza," he said. "Our results underline that we also need
contemporary studies of measles transmission in schools when it occurs.
More generally, our paper emphasizes the importance of digitizing the
rich trove of historical data on transmission of infectious disease, as
the Wellcome Library did with these data."
"These results highlight the importance of sustaining high measles
vaccination coverage among school children," said William Moss, a Johns
Hopkins University professor of epidemiology, who is familiar with the
research but had no role in it. "Because of the high transmissibility of
measles virus within schools, outbreaks will occur among the
unvaccinated school children should an infectious individual enter the
school," he said.
The researchers show that at small spatial scales such as schools,
highly contagious pathogens can behave with a complexity that becomes
obscured in large-scale transmission data from a city or national level,
A "notable aspect of this research relates to understanding how the
more complex dynamics of measles-virus transmission at fine spatial
scales such as schools relates to more regular and predictable dynamic
patterns at larger spatial scales," Moss said. "The findings are
specific to measles but these methods could be applied to other
infectious diseases with different and complex dynamics at different
In addition, the researchers' application of 1904 data to a current
public health scenario illustrates the value of historical information
in understanding how diseases spread, Moss said. After all, he said,
while society has changed since then, measles has not.
"Measles has a characteristic clinical appearance and during
outbreaks does not need laboratory confirmation, which didn't exist in
1904," he said. "This shows the value of searching for such data sets
and of the stories they can tell that are still of relevance more than
100 years later."
Becker and Grenfell worked with Ruthie Birger, a former graduate
student in ecology and evolutionary biology now at Columbia University;
Aude Teillant, a former research assistant in the Princeton
Environmental Institute now at the University of Caen Normandy in
France; and Paul Gastanaduy and Gregory Wallace of the Centers for
Disease Control and Prevention.