Experts calculate that coronavirus delta strain will be predominant in Spain in a month

In Spain, the delta strain of the coronavirus, first detected in India, is not yet officially considered a “variant of concern” (VOC) – a category used for strains for which there is evidence of an increase in transmissibility, more serious disease and reduced effectiveness against vaccines. According to the latest report from the Spanish Health Ministry, the delta variant accounts for less than 1% of new cases and is a “variant of interest” (VOI) – the category below VOC.

But the weeks-long delays with the sequencing of new infections mean it is difficult to know the true spread of the strain, and some experts believe the delta variant will be dominant in Spain in the space of a few weeks. How will this affect the progress of the pandemic? It is difficult to make exact forecasts, but the situation in the United Kingdom, where the delta strain has spread rapidly, offers some clues.

In the UK, the delta variant went from accounting for just a few cases to nearly all of them, in the space of two months. It is the “natural dynamic of the epidemic,” says Clara Prats, a researcher from the computational biology and complex systems group at Catalonia’s Polytechnical University (UPC). “New variants arrive and when one is more transmissible than the earlier one, it overtakes it. That is what happened with the alpha [variant first detected in the UK].”

In Spain, the delta variant will become the dominant strain in less than a month, according to the calculations of Álex Arenas, a physicist who is an expert in using mathematical models to predict the spread of the virus. This estimate is based on the spread of the delta strain in Catalonia, where it accounts for 20% of new cases. “In Spain, the data is not as clear, but based on the spread in Catalonia, it can be inferred that it will be dominant by mid-July,” he explains.

According to official statistics, the delta variant accounts for less than 1% of coronavirus cases, but this figure is based on outdated data from the genome sequencing of infections carried out up to four weeks ago. And the strain is spreading exponentially. In the United States, which has declared it a VOC, the variant accounted for just 0.6% cases in April, 1.3% at the beginning of May and 2.5% this month. It is likely to also become the dominant strain in a matter of weeks.

All the data indicate that the delta variant is more contagious, but this still needs to be confirmed in the laboratory. Preliminary information also indicates that it causes more hospitalizations, but is not more lethal. Studies in the UK have, however, revealed that while Covid-19 vaccines are just as effective against the delta strain as the alpha, they are less effective when only one shot has been administered. Given the UK prioritized the first dose in the vaccination campaign, this may be one of the reasons why coronavirus cases have been on the rise in the country for nearly a month – a situation that has forced the government to pause the deescalation of restrictions.

Spain took the opposite approach and is one of the European countries that has the highest percentage of fully vaccinated citizens. But only one-third of the over-60s are fully vaccinated, as this group is receiving the Oxford-AstraZeneca vaccine, whose second shot is administered 12 weeks after the first under Spanish health guidelines. Of the five million people who received the first AstraZeneca dose, only one million are fully vaccinated.

In the UK, the delta variant is also causing different symptoms, such as a runny nose.

On how the new strain will affect the epidemiological situation in Spain, experts are hesitant to make predictions. José Jiménez, a researcher on infectious diseases at King’s College in London, says it will depend on the coronavirus restrictions and how people respond. “This is what we saw with the alpha variant, in some places it was said to be more contagious and more lethal based on what we saw in the United Kingdom in the earlier wave. However, and fortunately, that was not the case in other countries such as Spain, where it became dominant but did not lead to hospitals becoming overwhelmed to the same degree we saw in the United Kingdom,” he explains.

Prats warns: “What we have to prevent is the proliferation of superspreader events. We would be able to manage a soft rise [in cases], but a fast rise would be unsustainable with the measures we have now.”

While some countries have taken measures to stop the spread of the delta variant – Germany has closed its border to the UK – Spain has not and travelers from Britain are allowed into the country with no need for a coronavirus test. “I don’t think [the delta variant] will have a significant impact – it could have one, but we shouldn’t alarm people more than necessary,” said Fernando Simón, the director of the Health Ministry’s Coordination Center for Health Alerts (CCAES), last Monday.

English version by Melissa Kitson.