Memorandum by the Health Protection Agency
The Health Protection Agency notes that the
House of Lords Science and Technology Committee intends to inquire
into air travel and health and in particular to look at developments
since 2000 when it published its last report on this subject.
The Agency was established in April 2003 and
therefore did not contribute to the original report. However the
parts of the report relating to new health concerns and the risk
of transmission of infection now lie within the Agency's area
of statutory responsibility and we wish to take this opportunity
to offer our views to the Committee.
The Agency is aware of no new or emerging health
concerns that are specifically related to flying.
We would distinguish between health concerns
that are specifically related to flying and those where air travel
might have an influence on the spread of a health hazard or affect
the course of a disease outbreak.
Although SARS was perceived as an example of
the latter threat when the original report was published, it is
not currently seen as a significant global public health threat.
The issues raised are now best considered in the context of a
possible influenza pandemic, but with the benefit of learning
from the global SARS experience.
The influence of air travel might arise in two
ways: (1) the speed of travel by air, particularly for long distance
travel, and (2) any unique quality of the aircraft that facilitated,
or inhibited, spread of an infectious agent or other health hazard
while on board.
The impact of the speed of long distance air
travel (compared to land or sea) is that it might allow passengers
to arrive at a destination while still infectious whereas those
travelling by slower transport would have either recovered or
succumbed before arrival. This has always been a risk as travel
times reduced. The keys to reducing the risk are to discourage
people from flying if they are unwell and to respond appropriately
when ill passengers disembark.
Within its pandemic influenza contingency planning
the Government has developed advice on travelling in the period
before a possible pandemic in line with WHO advice. Advice has
also been produced for British nationals living abroad about travel
arrangements in advance of a possible pandemic.
Systems are in place within the aviation sector
for port health authorities to be notified when an incoming plane
has ill passengers on board so that appropriate arrangements can
be made at the airport to receive and assess the passenger. These
systems are activated for a number of illnesses and would be in
place in the early stages of a possible pandemic.
The potential impact of restricting travel on
the evolution of a possible pandemic is considered later.
Concerns about the transmission of infection
during a flight centre principally on respiratory illnesses. As
noted above the concerns initially focused on SARS but are now
more often considered in the context of a possible pandemic influenza.
The key questions focus on the method of transmission
of an infection from one person to another in an aircraft and
particularly on the relative contributions of large droplet and
contact transmission versus aerosol spread. Aerosol spread, if
it was a significant factor, would potentially result in wider
spread in an aircraft.
In general epidemiological studies suggest that
the air systems within an aircraft are not conducive to the easy
spread of infection through the aircraft. In those cases where
on-board spread has been documented it has generally been restricted
to the immediate environment of a sick passenger; similar risks
would apply to other modes of travel apart from aircraft or indeed
to close, prolonged social or domestic contact.
With particular regard to a possible influenza
pandemic, the HPA has examined the data upon which to base any
judgement about modes of transmission of influenza virus within
Currently there are multiple competing hypotheses,
a lack of reproducible experimental findings and frequent extrapolation
from experimental and animal models in scientific papers. Nevertheless,
most data point towards short-range transmission in real-life
settings and this pattern of transmission is known to be associated
with spread by large droplets and contact transmission. Although
there is insufficient data to determine any additional role which
aerosol spread may play this is currently felt to be minor.
Papers which suggested aerosol transmission
onboard aircraft were flawed by significant movement throughout
the cabin and by contact on ground transport and in lounge areas,
as well as extended time grounded with the ventilation system
In the light of these concerns the HPA has examined
the evidence on the potential impact of travel restrictions on
a possible pandemic.
This suggests that imposing an almost immediate
90% restriction on all air travel to the UK when a pandemic is
thought to be imminent would delay the peak of a pandemic wave
by only one to two weeks. Restrictions limited to travel from
South East Asia would be necessarily less effective as there would
be indirect flows of people from Asia into the UK, as well as
people infected in outbreaks in other countries.
Assuming passengers were screened before travel
for clinical symptoms (in countries where there were known to
be clusters of cases) there is no additional advantage in entry
screening. Even if successful in preventing all those with clinical
symptoms from travelling this is only likely to delay the spread
of disease by one to two weeks.
1. Definitive new studies are needed which
will help to illuminate the scientific uncertainty about modes
of transmission of influenza virus.
2. Although notification of ill passengers
is a tried system for individual passengers it has not been tested
in the context of an evolving pandemic when multiple ill passengers
might be expected. A live operational field exercise with the
aim of testing reception arrangements for an aircraft with symptomatic
passengers returning from an affected area of the world would
be beneficial. The aim would be to validate draft emergency plans
and identify appropriate staff training.
18 June 2007