Select Committee on Science and Technology Written Evidence

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 an aircraft.

  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 switched off.


  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

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