Go to gate: COVID-19 imported cases in Madrid and the potential role of airport transmissions.

Data on imported cases of COVID-19 are scarce. Recorded imported cases in Madrid, Spain represented 0.08% of the total cases from May to December 2020, as reported by the Epidemiology Service of Madrid Autonomous Community. We reflect on the potential role of airports in infection transmission, the current preventive measures to avoid travelling-related infections and discuss if there is a real need to focus on strict airport controls when community transmission is ongoing.

Air travel has notably contributed to the worldwide spread of coronavirus disease (COVID-19), accelerating the pandemic. Airports represent a likely gateway for COVID-19 since it gathers both in-flight transmission and transfer of infected passengers between countries.[1] In order to control the pandemic, many countries have implemented border restrictions to prevent the arrival of infected travellers from countries where there is continuing community transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Spain has been hit hard by COVID-19 and to date more than 1.7 million cases have been reported.[2] In the early stages of the pandemic, in an attempt to control the dramatic increase in infections, the Spanish government implemented a state of alarm from 14 March to 21 June 2020. It included, among others, rigid restrictions on air route entries and a 14-d quarantine on those travelling due to events of force majeure.

Spain is one of the largest tourist destinations in the world. The main Spanish airport, Adolfo Suarez Madrid-Barajas, located in the capital, receives millions of tourists every year. In 2019, Madrid airport registered more than 61 million travellers, of whom nearly 45 million were international passengers. These figures drastically changed with the pandemic, with a 69.7% reduction in flights.[3]

However, once the state of alarm ended, there were no specific restrictions for international travel to Spain. Unlike other neighbouring countries, such as Italy or Germany, no microbiological test was initially required to enter the country, which led to a big controversy among Spanish political and health authorities. In November 2020, while Spain underwent a second wave of the pandemic, the airport protocol was amended to include a mandatory negative PCR for COVID-19 in people travelling from high-risk countries.

To explore the importance of the airport acting as a SARS-CoV-2 virus gateway in Madrid and, therefore, whether implementing measures such as requesting microbiological tests should be necessary in Spain, we reviewed the official data from the Epidemiology Service of Madrid Autonomous Community. This service contacts every PCR-positive patient for an epidemiological survey, including extensive travel information, classifying cases as imported if the patient was out of Spain for the entire incubation period. During 11 May–13 December 2020, there were 237 confirmed imported cases of COVID-19. Of these cases, 56.5% were male, 64.4% were in the 30–69 y age group, 45.6% came from the Americas and the majority occurred in July 2020 (34.2%). The countries of origin of the imported cases were most often the Dominican Republic, Portugal and the USA.[4] Since during the same period a total of 304 616 cases of COVID-19 were reported in Madrid, imported cases represented 0.08% of the total number.

Besides a mandatory pretravel PCR for people arriving from countries with a high risk of COVID-19, travellers passing through Madrid airport routinely undergo three sets of controls to screen for imported cases: a documentary one, answering a digital questionnaire about their state of health and habits; a visual one if they present perceptible symptoms; and a body temperature control, whereby those with a temperature of >37.5 degrees are considered suspicious cases and consequently are subjected to further investigation. These combined activities, in light of the negligible low contribution of international travel to the burden of COVID-19, might be sufficient.

The European Centre for Disease Prevention and Control Aviation Health Safety Protocol currently does not recommend quarantine or systematic testing for SARS-CoV-2 for air travellers.[5,6] We agree with this statement, as data from Madrid imported cases—even if contact tracing was imperfect and there were some missed reported imported cases—appear to confirm that the relative significance of imported cases is probably small compared with ongoing transmission. This consideration is also supported by mathematical models that attempted to evaluate the impact of airport control and travel restrictions, suggesting that strict, untargeted limitations to movement are probably unjustified in countries with high COVID-19 incidence.[7] Social distancing, restricted crew/passenger interaction and face masking are basic measures that are likely to prevent the transmission of COVID-19, but we wonder if pretravel testing or ‘immunity passports’ would be of any additional use in the current epidemiological situation.

In 2021, where inequity in vaccine provision is likely, a scenario with a disparity in prevalence between countries represents a challenge in terms of travel. New strategies to enable the follow-up of travellers may be required. Some have already been suggested, such as the combination of quarantine and a single test at around day 7 after arrival, which appears to be a reasonable alternative to longer quarantine without testing.[8] It is also likely that selective restrictions will probably focus on people travelling from countries with high COVID-19 prevalence to countries where virus transmission has significantly decreased or even disappeared. In times when personal freedom is highly valued, governments, scientists and regulatory agencies should work together and attempt to provide recommendations that protect both community and individual rights.