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COVID vaccination, PCR testing and variant sequencing: The key to safe cross-border travel

With many people ditching staycations for trips overseas, the risk of traveller related introduction of high-risk COVID19 variants into the UK is a major issue surrounding European and international holiday travel. The UK government day 2 and day 8 covid international testing programme to mitigate this risk is one of the most stringent travel testing initiatives globally. PCR testing and genomic sequencing for UK arrivals coupled with successful vaccine rollout is proving key to safe overseas travel.

In a landmark paper investigating cross border COVID transmission, published online in EClinical Medicine by the The Lancet publication, Prof Williams and Dr Loddo of Oncologica show data indicating that although vaccines are having a big impact, there is still a high prevalence of high risk SARS-CoV-2 variants entering the UK which could potentially undermine the vaccination programme gains.

The Oncologica genomic laboratory uses very sensitive PCR testing techniques coupled with fast semiconductor sequencing technology, which enables the precise identification of variants of concern. In this study relating to 203,065 passengers’ tests, around 2 in every 100 travellers were found to have infection involving a broad range of COVID variants. The low sensitivity of pre-embarkation lateral flow testing may contribute to the high prevalence observed in travellers.

The UK government’s day 2 day 8 stringent PCR travel testing programme highlights the importance of monitoring cross border transmission, and the crucial role it is playing in protecting the integrity of the UK national vaccine programme against the import of high-risk variants with immunity evading properties.

The adoption of similar PCR COVID testing strategies in many countries is gaining importance globally as the numbers of new cases of SARS-CoV-2 has nearly doubled over the last 2 months. Therefore, the chances for the emergence of new high risk COVID-19 variants is potentially high. 

The study also shows that two doses of the vaccine are highly effective at reducing asymptomatic infection. However, a significant proportion of fully immunized travellers harboured active COVID SARS-CoV-2 infection and there was no difference in the amount of virus particles, referred to as viral load, when comparing vaccinated versus non-vaccinated individuals.

The data indicates that vaccine passports or immunity certificates alone may not be adequate, and need to be supported by Covid PCR testing and sequencing.  Interestingly the measurable amount of virus of the Delta variant was found in the Oncologica study to be 21-fold higher compared to the Kent variant and this supports the higher transmissibility of this variant now the most dominant in the UK.

Combining rigorous travel PCR testing and sequencing together with vaccination is likely to provide the best opportunity for safe international travel vital for the economy and leisure travel.  Such public health COVID detection measures combined with national NHS track and trace will enable normal activities to resume until the goal of global vaccination is achieved.

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