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| Scheduled airline traffic around the world, circa June 2009 – Credit Wikipedia |
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Just over three weeks ago, in WHO Guidance: Non-pharmaceutical Public Health Measures for Mitigating the Risk and Impact of Epidemic and Pandemic Influenza, we took our first look at the World Health Organization's recently released 91-page NPI Guidance document.
Since then we've taken a closer look at the WHO's recommendations on Personal protective NPIs (hand hygiene, isolation, masks, etc.), Social Distancing, and most recently Environmental Measures.NPIs - or Non-Pharmaceutical Interventions - are those actions (apart from taking vaccines & antivirals) that individuals and communities can do to help slow the spread of an infectious disease.
None of these measures will stop a pandemic virus from spreading, or fully protect an individual from infection. Their combined use, however, can help slow the spread of the virus and (hopefully) reduce the impact of a severe pandemic.The last category of NPIs to look at from this WHO document involves travel, both domestic and international. As the graphic at the top of this blog suggests, international airline traffic will play a big role in the rapid and efficient spread of the next pandemic virus.
The WHO NPI recommendations are divided into 4 categories.
- Travel Advice
- Entry & Exit Screening
- Internal Travel Restrictions
- Border closure
The least controversial of these recommendations is the issuance of travel advice, as we see this done routinely today, through the CDC's Traveler's Health website, through signage at airports, and other venues.
As with many of the other NPI recommendations we've looked at, there isn't a great deal of evidence of its effectiveness, but it is fairly easy to implement, has few downsides, and probably has some merit.
The second NPI considered is Entry and Exit Screening of travelers, which we've seen rolled out for the 2009 H1N1 pandemic, Ebola, MERS, and other localized outbreaks of exotic diseases.
While highly disruptive, and generally ineffective (see Why Airport Screening Can’t Stop MERS, Ebola or Avian Flu) it is often the first - and most visible - response by governments anxious to show they are `doing something' to protect the populace.
Entry and exit screeningIn 2010, in Japan: Quarantine At Ports Ineffective Against Pandemic Flu, I wrote about a study that found between asymptomatic or mild H1N1 infections, and a silent incubation period of several days, there wasn’t much chance of long-term success.
Summary of evidence
Ten articles related to entry and exit screening were included in this review (185, 220-228). Observational studies conducted at airports estimated that the sensitivity of entry screening was low (226-228). Among arriving international travellers, half of the influenza cases were identified more than a day after arrival (through passive case finding and contact tracing in the community), although 37% of the influenza cases were screened while passing through the border entry site (185). Simulation studies estimated that screening international travellers may help to delay the epidemic by less than 2 weeks (0–12 days) (220-222).
For every person identified, and quarantined, by port authorities - researchers estimate 14 others infected by the virus entered undetected.In April of 2012, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we looked at a study that found that the screening methods used at New Zealand’s airport were inadequate to slow the entry of the 2009 pandemic flu into their country, detecting less than 6% of those infected.
While I suspect it will be widely ignored, the WHO's recommendation is against Entry and Exit Screening.
Moving on, travel recommendation #3 involves Internal travel restrictions (note: This WHO NPI guidance document did not address International Travel Restrictions).
Summary of evidence
One epidemiological study (231) and four simulation studies (114, 162, 232, 233) related to internal travel restrictions were included in this review. A time-series analysis study conducted in the USA showed that frequency of domestic airline travel is temporally associated with the rate of influenza spread, and following the September 11 attacks in 2001, a reduction in such travel delayed the epidemic peak by 13 days compared with the average for other years (231).Presumably, very early in a pandemic, if a nation finds itself with a single hotspot of disease transmission, it might consider restricting travel to or from that area in an attempt to slow the outbreak.
A simulation study predicted that implementation of a strict travel restriction (95% travel restriction, enforced for 4 weeks) could reduce the epidemic peak by 12%, and a moderate restriction (50% travel restriction, enforced for 2–4 weeks) could delay the pandemic peak by 1–1.5 weeks (162). Another simulation study predicted that an internal travel restriction of more than 80% could be beneficial (232). A strict internal travel restriction (90%) was also consistently found to delay the epidemic peak by 2 weeks in the United Kingdom, and by less than 1 week in the USA (114). However, a 75% restriction had almost no effect (114).
Frankly, it is hard to imagine this situation occurring more than a few weeks into any pandemic, but it nonetheless is conditionally recommended during the early stage of a localized and extraordinarily severe pandemic outbreak.
And lastly, the WHO takes a very dim view of border closures of any kind, although they grant it might be effective for some small, self-sufficient island nations.
Border closure
Summary of evidence
Eleven articles related to border closure were included in the systematic review (114, 135, 204, 231, 235-239). Two were epidemiological studies (135, 231) and nine were simulation studies (114, 204, 234-240). An epidemiological study suggested an important influence of international air travel on the timing of influenza introduction (231). Another historical analysis of the 1918–1919 pandemic suggested that strict border control was a successful method for delaying and preventing influenza from arriving in South Pacific islands (135).
A simulation study predicted that 99% restriction of cross-border travel between Hong Kong SAR and mainland China may delay the epidemic peak by about 3.5 weeks compared with non-travel restriction (235). Another simulation study conducted in Italy predicted that international air travel restriction would delay the peak of epidemic by about 1–3 weeks, depending on the transmission rate and the level of restriction (204). However, the attack rate was not significantly affected (204).
Furthermore, simulation studies based on a global scale model also predicted that international travel restriction would delay epidemics by about 2–3 weeks (236) and significantly delay its global spread (5–133 days) (237).
Strict border control of 99.9% may be effective in delaying the epidemic peak by 6 weeks, while 90% and 99% border control would delay the epidemic peak by 1.5 and 3 weeks, respectively (114). International travel restriction is estimated to slow the importation of infections (234, 238), but would not reduce the epidemic duration (238).
Because the supply of essential items to a population, such as food and medical supplies, often relies on importation, strict border closures need to be carefully considered before implementation in island countries and territories (239).
Much like Entry and Exit Screening, border closures sound like a reasonable step during a pandemic (and I'm sure will be tried by some countries), but - at least with influenza - is unlikely to be effective.
During the 1918 pandemic, when international travel was far less common, a few nations managed to block entry of the pandemic virus by imposing a strict quarantine of all arriving passengers (see Protective Effect of Maritime Quarantine in South Pacific Jurisdictions, 1918–19 Influenza Pandemic).
The four successful quarantines during the 1918 pandemic were in American Samoa (5 days' quarantine) and Continental Australia, Tasmania, and New Caledonia (all 7 days' quarantine).
- The Spanish Flu did not reach American Samoa until 1920, and had apparently weakened, as no deaths were reported.
- Australia's quarantine kept the influenza away until January of 1919, a full 3 months after the flu has swept New Zealand with disastrous effects.
- Tasmania kept the flu at bay until August of 1919, and health officials believed they received an milder version, as their mortality rate was one of the lowest in the world.
- By strictly enforcing a 7-day quarantine, New Caledonia managed to avoid introduction of the virus until 1921.
Eleven years ago, in New Zealand: Testing Pandemic Quarantine Plans, we looked at Exercise Spring Fever - a `war game' designed to test New Zealand's ability to cut themselves off from the rest of the world during a pandemic.
While no decision has ever been made regarding the quarantining of New Zealand during a pandemic, the option continues to be discussed.Last year, a study published in Australia & New Zealand Journal of Public Health, looked at the economic impact of a 180-day quarantine on the island nation of New Zealand.
Economic evaluation of border closure for a generic severe pandemic threat using New Zealand Treasury methods
Matt Boyd, Osman D. Mansoor, Michael G. Baker, Nick Wilson
First published: 08 August 2018
ABSTRACT
Conclusions: This work quantifies the economic benefits and costs from border closure for New Zealand under specific assumptions in a generic but severe pandemic threat (e.g. influenza, synthetic bioweapon). Preparing for such a pandemic response seems wise for an island nation, although successful border closure may only be feasible if planned well ahead.
Implications for public health: Policy makers responsible for generic pandemic planning should explore how border closure could be implemented, including practical and legal frameworks.
Whether New Zealand would actually `pull the trigger' is unknown, but they are probably the largest population island with a reasonable chance of success.
This 5-part series on the WHO's updated NPI guidance only covers the highlights of more than 200 pages of documentation. Policy makers will want to delve deeper into the source documents.
These recommendations are just that; recommendations.Not all will be adopted - or universally followed - by nations, communities, or individuals around the globe. What may work in Europe or North America may not work nearly as well in Asia, or Africa.
In the opening weeks, and likely months, of the next influenza pandemic vaccines and antivirals will likely be either unavailable, or in very short supply. NPIs, while far from perfect, offer us the `next-best' thing we can do to reduce the spread, and impact of a pandemic.
