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Mandatory COVID-19 swabs for passengers arriving from China at Milan Malpensa International Airport, Italy, 29 December 2022. Credit: Marfisi/AGF/Shutterstock.

Italy was the first European country to impose pre- and post-flight testing to travellers coming from China, in addition to sequencing positive samples at arrival. Other European countries have followed, and on 4 January the European Union recommended pre-flight testing to all travellers from China to the EU. It was a response to a huge wave of infections and severe cases in China, following the ending of the country’s zero-COVID policy.

The Italian Ministry of Health explained in a 30 December press release that the new measures are meant to reduce the risk of importing new variants from China. Nature Italy talked to Stefano Merler, a mathematical epidemiologist at Fondazione Bruno Kessler in Trento who advised the Italian government in the first two years of the pandemic, about the efficacy of such measures.

Governments have resorted to air travel control measures a few times during the pandemic. A travel ban on China was imposed in February 2020 by most countries. Then, at the end of 2021 the United States and most European countries banned travels from a handful of Southern African countries to keep out the Omicron variant. What did we learn from those experiences?

Even before COVID-19, we knew that mobility restrictions can have a sizable impact only if they are taken globally and quickly. COVID-19 being a largely asymptomatic disease made things much more difficult. Several studies have shown that the 2020 travel ban on China has delayed the surge of the epidemics in the rest of the world by a few weeks at most. This is mainly because travel was stopped nearly two weeks after the first exported cases were detected in Thailand, Japan, and South Korea. The same happened with Omicron: when the ban was imposed, the variant was outside southern Africa. We have not prevented the spread of a single variant with this kind of measure, and this time will be no different.

As for sequencing positive swabs of incoming travelers, what impact might it have?

It will help to monitor what virus variants arrive in our country, and this is helpful. This does not mean that we will keep new variants out, since travellers from China could easily reach our country with a stopover somewhere else. Italy had already set up a surveillance system on the virus genome in April 2021, called the Italian COVID-19 Genomic platform. It was designed by Istituto Superiore di Sanità to answer public health questions, namely whether the drugs we have at our disposal, such as vaccines, antivirals, and monoclonal antibodies, are effective on the circulating variants.

How many samples are sequenced by this surveillance system?

Nearly 1000 samples per week and ISS publishes a monthly report. This number is sufficient to detect variants with up to 0.5% prevalence, and sequencing is directed towards infections that are more likely caused by new concerning variants. These include patients in hospitals and ICUs, reinfections, immunocompromised subjects, people coming from countries that are under the watch of international health organizations. China was already on our radar before the latest rules were introduced. In addition to this, we also do monthly flash surveys focusing on known variants of concern.

What kind of questions are the flash surveys addressing?

We [at Fondazione Kessler] set up these surveys together with the ISS in January 2021 to estimate to what extent Alpha was more transmissible than the most prevalent variant circulating in Europe at that time. To estimate the transmissibility, we needed to measure how the prevalence of the variant grew over time. We assumed an initial prevalence of at least 5% and calculated the fraction of positive samples that each region should sequence to obtain a statistically reliable measure. We repeated the survey monthly. That initiative informed the measures adopted by the government during the first months of 2021. The surveys then became structural and when the Omicron variant emerged, they were run on a biweekly basis.

Other countries, such as the UK, are sequencing much more. Should Italy scale up its efforts?

Given budget constraints, Italy is doing well. Of course, one could consider expanding the sequencing campaign but always keeping in mind that any initiative should be designed to answer a specific question. The UK is certainly not wasting its money, and its contribution to global scientific knowledge on this virus is paramount