New evidence bolsters case for Covid-19 testing on arrival

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New independent analysis has found “significant methodological concerns” in work by Public Health England (PHE), which means the detection rates for passenger testing on arrival are being “significantly understated”.

The work was carried out by Edge Health and Oxera.

Unlike more than 30 countries, including Germany and Italy, the UK has not introduced any form of scheme to test travellers for Covid-19.

Instead the country is implementing a 14-day quarantine policy and establishing ‘travel corridor’ countries and islands that are exempt (passengers do not have to isolate).

This policy – widely criticised by the travel industry – is driven in part by evidence from PHE that testing on arrival at an airport would identify only seven per cent of virus cases.

A new review, which has been authored by leading consultants and supported by academics including Kit Yates, co-director of the Centre for Mathematical Biology at the University of Bath, finds that the PHE paper is based on a theoretical model that does not account for real-world data and therefore underestimates the rate of detection from airport testing on arrival.

In reaching its seven per cent conclusion, PHE does not take account of potential travellers who are in theory detectable or symptomatic before the flight takes off.

But these travellers would be detected by an on-arrival testing scheme if they flew to the UK and therefore need to be accounted for in considering the effectiveness of a testing regime.

By contrast, although the review also identifies shortcomings with the LSHTM and APHA outputs, the LSHTM paper finds that an on arrival test would reduce the number of infectious travellers released into the community by about 45 per cent, and the APHA paper quotes detection rates of 39.6 per cent for a testing on arrival scheme.

Edge Health and Oxera estimate that up to 63 per cent of infected passengers attempting to enter the UK could be prevented from doing so with an on-arrival testing scheme – vastly higher than the figure offered by PHE.

Other key findings of the review include:

  • Both PHE and LSHTM assume 100 per cent compliance with quarantine, which is not supported by recent evidence, and therefore should be considered in determining how to open up safe travel to and from the UK. For example, according to evidence from SAGE, only around 20 per cent of those reporting symptoms of Covid-19 in England report fully self-isolating.
  • The effectiveness of testing regimes should take account of the demographics of infected people in a country of origin, and particularly the demographics of those people who are likely to fly. The PHE model does not do this.
  • As all three papers are based on a simulation modelling technique known as Monte Carlo simulation, it is important to align the assumptions and the outputs with real-world evidence, which is currently lacking in the three papers’ approach. In addition, the assumptions in the three papers vary considerably and, in a number of cases, are not based on the most recent empirical evidence.
  • The papers assume that the objective of the testing strategy would be to reduce the risk of ‘seeding’ community transmissions from flight passengers to zero. However, the government has established travel corridors based on an acceptable level of risk, rather than zero. These two positions are inconsistent.

George Batchelor, cofounder and director of Edge Health, said: “The way in which the PHE model is set up means that only a tiny proportion of infected passengers – those who become symptomatic or are asymptomatic but detectable by a PCR test during the flight – can be detected at arrival.

“This means the widely quoted seven per cent excludes anyone who is in theory detectable or symptomatic before the flight takes off.

“This evidently isn’t the case, and it leads to an underestimation of the effectiveness of testing on arrival (the seven per cent figure), raising serious questions about its role in informing government policy on passenger testing.”

The review has been submitted to the UK government global travel taskforce, which is due to report on new quarantine measures at the start of next month.

The findings of the new report were supported by Shai Weiss, chief executive of Virgin Atlantic, who said: “This new and independent analysis identifies flawed and outdated assumptions in that modelling, and reveals that testing will capture a vast majority of cases rather than the purported seven per cent, which makes it the right solution.

“We urgently need the introduction of a passenger testing regime here in the UK to safely replace quarantine and support the UK’s economic recovery, which relies on free-flowing trade and tourism.

“Half a million UK jobs depend on a fully functioning aviation industry, therefore it’s vital that policy decisions are based on the latest possible evidence.”

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