0:06
In this part, I will talk about school closures,
a non-pharmaceutical intervention
at the community level.
After completing this part,
you should be able to explain
why school-age children are important
in transmission of some infectious diseases,
to describe the potential impact of school closures,
and to discuss the practical difficulties
associated with closing schools.
It is well known that school-age children
are of primary importance in the transmission
of many respiratory infections in the community.
A survey of social contact patterns,
in eight European countries,
identified children as the group
with the greatest frequency of contacts.
The heat plot, shown here,
indicates the frequency of social contacts,
with highest frequency shown in white.
We can clearly see the frequency
of contacts between children is high.
The diagonal band indicates that contacts
tend to be most frequent
among people of similar ages,
and the two off-diagonal bands show the contacts
between children and their parents.
The investigators considered what would happen
if a new pathogen emerged
in a completely susceptible population
and was spread through close contacts
as, for example, a respiratory virus might be.
Based on these patterns,
the investigators determined
that incidence of infections with the new pathogen
would be highest in children.
1:23
Influenza virus spreads through close contact,
and rates of infections in children
tend to be higher than in other age groups
in influenza epidemics and pandemics.
That is not to say that children
have the greatest burden of severe disease,
because influenza virus infections are often milder
in children than in adults and the elderly.
Because of the high rate of infections in children,
and particularly in schools,
the closure of schools during epidemics
is a non-pharmaceutical intervention
with particular promise.
Going back a hundred years,
the 1918 influenza pandemic
had a devastating impact on the world.
School closure was a common intervention
used in many locations to try to slow transmission,
and there is some evidence
that early implementation
of school closures was effective.
School closures were also used
in other pandemics and epidemics.
In the 21st Century, here where I am in Hong Kong,
authorities closed schools for three weeks
during the peak of the SARS epidemic in 2003,
and, more recently, schools were closed to control
influenza epidemics in 2008 and in 2009.
In March 2008,
at the height of the winter influenza season,
and following three pediatric deaths
associated with influenza,
the government announced that it would close
all nurseries, kindergartens, and primary schools
the following day, for a week.
This would then be followed, immediately,
by the scheduled one week Easter break,
for a total closure period of two consecutive weeks.
We can look at what happened,
and try to make some inferences
about the impact of school closure.
Here we can see the weekly consultation rate
of influenza-like illnesses in Hong Kong,
and the weekly detection rates
of influenza viruses in children and adults.
Infections peaked in mid to late February,
and incidence rates were declining
by the school closure period
that started on the 13th of March.
Rather than try to directly interpret
changes in the epidemic curves,
we used a statistical approach
to estimate the daily reproductive number.
Shown here, the reproductive number
dipped below one just before the peak in incidence,
and was declining throughout early March,
or there was a decline in transmission
during and after the closure period,
this most likely reflects the waning
in the epidemic that would have occurred
regardless of the school closures.
3:39
Since the emergence of avian influenza A (H5N1),
the past 10 years have seen intensive preparations
for the next influenza pandemic.
In the early years of the 21st Century,
many plans were based on the potential
for another pandemic like 1918,
stimulated by the severity
of human infections with H5N1.
Many local and national administrations
included school closures in their plans
for the response to a new influenza pandemic,
as part of a broader range of measures
that could be implemented
depending on the local situation
and the estimated severity
of the new pandemic virus.
Those pandemic plans were put to the test in 2009
when swine flu emerged, first in North America,
and rapidly spread around the world.
Within days of the announcement of the identification
of the new H1N1 strain of swine flu,
and its potential to cause a pandemic,
the administration in Hong Kong
announced their plans for responding.
Part of the response would include
school closures for at least two weeks,
once the first non-imported case was identified,
indicating that transmission
was occurring in the local community.
What actually happened is that despite
imported cases being identified
throughout May and early June,
the first non-imported case was not identified
until June the 9th and, on June the 10th,
the announcement was made
that nurseries, kindergartens, and primary schools
would all close for two weeks.
Secondary schools were only closed
if swine flu cases were identified in that school.
Subsequently, the school closures were extended
to the start of summer vacation in mid July,
and lasted for around a month in total.
We examined the impact of the school closures
on the course of the first wave
of pandemic H1N1 in Hong Kong.
We constructed a transmission model
with three age classes:
children less than 12 years of age,
children 13 to 17 years of age,
and adults 18 years of age or older.
In the absence of local data on social contacts,
we used the European data to parameterize
the relative transmissibility
within and between age groups,
and we allowed susceptibility to vary by age.
We then estimated the changes
in the proportion of infections
that were notified over time,
called the reporting rate,
and the change in transmissibility
associated with the school closures
in younger children
and the school vacation in all children.
Here are our results.
We estimated that transmission
within children dropped 70%
during the school closures and summer vacation,
with a reproductive number
of 1.7 before June the 11th,
1.5 between June the 12th and July the 10th,
and 1.1 after July the 10th.
As part of the model,
we estimated that reporting rates began to decline
in mid-June and stopped declining on June the 29th,
with a final reporting rate of 5.2%.
This is very consistent
with a separate serological study,
in which we estimated that 3.9% of infections
were laboratory confirmed.
We also estimated that children were 2.6 times
as susceptible to infection as adults,
consistent with a separate study,
in the United States, in which children
were twice as susceptible to infection.
In conclusion, we demonstrated
that school closures reduced overall transmission
by 25 percent, and delayed the peak in H1N1 incidence
to September, when schools re-opened.
Other studies have demonstrated
significant impact of school closures
in the 2009 pandemic,
while simulation studies have shown
how this type of intervention
can flatten the peak of an epidemic,
reducing both the peak attack rate,
which can help to prevent hospitals
from being overwhelmed, and also reducing
the cumulative incidence of infections.
Having presented the benefits of school closures,
I will finish with a few comments
on the limitations of this intervention.
In many locations in which it is common
for both parents to work,
school closures can cause major disruption
and economic loss to families because of the need
to arrange child care at short notice.
In addition, many children in deprived areas
are reliant on subsidized school meals.
School closures are therefore likely to be considered
only in the most serious situations,
such as severe influenza pandemics.
Gabriel M. Leung (HKU)Dean
Joseph T. Wu (HKU)Associate Professor
Kwok-Yung Yuen (HKU)Professor
Tommy Lam (HKU)Assistant Professor
Maria Huachen Zhu (HKU)Associate Professor
Guan Yi (HKU)Chair Professor
Benjamin Cowling (HKU)Professor
Thomas Abraham (HKU)Associate Professor
Mark Jit (LSHTM)Professor
Malik Peiris (HKU)Chair Professor
Marc Lipsitch (Harvard)Professor
