Will this be Spain’s fifth and final coronavirus wave?

Epidemics are “very simple,” according to Miguel Hernán, an epidemiologist who teaches at Harvard University. “If there is a group that is susceptible to infection and measures are not taken, they will get infected. The question is how many and how quickly,” he explains.

This is what happened in the fifth wave of the coronavirus pandemic in Spain: young, unvaccinated people were exposed to a more contagious variant of the virus – the delta strain – as restrictions were lifted following the end of the state of alarm. This is what sparked the fastest rise in coronavirus cases Spain has seen since there have been reliable data.

The fifth wave appears to be easing, but the trend is not yet clear. Once transmission levels fall again, a situation that is likely to happen when the majority of the population is vaccinated against Covid-19, there will be a lot fewer people susceptible to the virus and there will be less likelihood of contagion rates rising back up to previous levels.

Several public health experts who spoke to EL PAÍS agree that there are two possible scenarios for what happens next. Everything depends on mutations of the coronavirus. In the best-case scenario, which most experts believe is more likely, the virus does not become more contagious nor more resistant to vaccines. In this situation, the fifth wave will ease during August, and, if the Covid-19 vaccination drive continues at a good speed, the percentage of people who are unvaccinated and haven’t contracted the virus will be small – primarily children, who in most cases, are asymptomatic or only experience mild symptoms. In this hypothesis, there will be new cases and more upticks in the epidemiological curve – given that the virus will remain with us for months and perhaps forever – if the complicated feat of reaching global group immunity is not achieved.

When the large majority of the population is vaccinated, there will be more coronavirus cases, but perhaps we won’t even know it, just like we don’t if there are a lot of colds

Miguel Hernán, professor of epidemiology at Harvard University

In the worst-case scenario, the virus mutates and is able to resist the current vaccines, and it spreads among those who have already been vaccinated – which is already happening, but only in rare instances – or worse still, the vaccines are no longer able to protect people from developing serious cases of the disease. This would not be a complete return to the starting point, but it would be a significant setback. There is a real threat that Spain could face new waves with large spikes in cases and that the country’s hospitals could once again be pushed to the breaking point. This would lead to the reintroduction of strict coronavirus restrictions and extend the health, economic and social crisis even longer. Experts believe this is the less likely scenario, but warn it is not impossible.

But these two scenarios are both simplifications. The future is not binary. Alberto Infante, who teaches at the National Health School of the Carlos III Health Institute, explains that a new variant may be able to resist vaccines and strain the country’s healthcare system but not overwhelm it completely.

Hernán, meanwhile, thinks the virus will slowly become endemic just like other coronaviruses that we live alongside. “When the large majority of the population is vaccinated, there will be more cases, but perhaps we won’t even know it, just like we don’t if there are a lot of colds in a season, because we don’t carry out systemic epidemiological vigilance, as it is not necessary,” says Hernán. “The coronavirus that today causes a cold likely caused a pandemic in its day.”

To reach this point, however, there is still a long path with many obstacles. Rafael Bengoa, an expert in public health and a former official at the World Health Organization (WHO), says that the first challenge to overcome is successfully deescalating the coronavirus restrictions introduced in the fifth wave. “We did not do this well with the fourth [wave] and we had the fifth. This could happen again. And with the delta variant, we have to be very patient because it is much more contagious. We must ensure we have two or three weeks with a very low incidence rate and in this case, we will have a good autumn,” he says.

But, will there be a sixth wave? Óscar Zurriaga, the vice-president of the Spanish Epidemiology Society (SEE), believes it’s possible, but that if it were to happen, the wave would be less widespread and less virulent – as long as there were no new mutations. “It shouldn’t be like what we are seeing now. It will be increasingly less severe, but we should still take it seriously, because people will continue to die and the health system, both primary healthcare centers and hospitals, will continue to be strained. In any wave, regardless of how mild it is, we run this risk,” he warns.

Once most of the adult population in Spain is vaccinated, the virus will spread primarily among those who have not received their shots. This was seen in the fifth wave, which saw a huge spike in cases among young, unvaccinated people. The rise in infections also affected older individuals, even those who were fully vaccinated, as the vaccine is not 100% effective, but the figures were much lower comparatively and there were fewer hospitalizations among vulnerable groups than in previous waves. Pedro Gullón, another member of SEE, believes that coronavirus cases in the future will be concentrated among age groups that have not been vaccinated and among people who have difficulty accessing the vaccine. “Seasonal fruit pickers, migrants in an irregular situation, people who have to actively seek out, could suffer outbreaks. The waves in the future will have increasingly less of an impact, both with respect to transmission and hospital admissions and deaths. It will be strange to see a wave like this one in the next few months,” he says.

Uncertainty over vaccination of children

Of the population who will still be unvaccinated in autumn, most will be children. Experts now say that due to the spread of more contagious strains of the virus, up to 90% of the population needs to be fully vaccinated in order to achieve group immunity. In order to reach this figure, Spain will need to immunize under-12s, who make up 11% of the population. But a Covid-19 vaccine has still not been approved for use in this age group, and research into this issue is not likely to be completed until the end of 2021 or the beginning of 2022.

The role that children play in the transmission of the virus or as a reservoir of it is still not known. Last year, schools showed community transmission of the coronavirus, but did not act as vectors.

Bengoa believes stricter measures are needed at schools, given that the delta variant is much more contagious. “We need to continue to create [class] bubbles in schools. It has to be an anti-delta bubble, which is not the same as the bubbles created last year,” says Bengoa. “In other words, face masks must be mandatory inside and outside for children, no matter what. A lot more ventilation, no matter what, and probably carbon dioxide sensors in schools.”

The main risk for children is not that they will develop a serious case of Covid-19, but rather long Covid. According to data from the Office for National Statistics in the United Kingdom, around 10% of children between the ages of two and 11 who contracted the virus, still had minor symptoms five weeks later such as fatigue, muscular pain and problems concentrating.

The coronavirus will no doubt continue to cause problems, regardless of whether or not there is another large wave of infections. And that is in the most optimistic scenario. Experts are trusting the Covid-19 vaccination drive to ensure these problems are only minor. Fernando Rodríguez Artalejo, a professor of public health at Madrid’s Autonomous University, highlights that as well as focusing on the percentage of fully vaccinated people in Spain, it is also important to study how the immunization drive is progressing in other countries. While the virus continues to circulate across the world, it is very likely that a new strain will emerge that rekindles the pandemic.

English version by Melissa Kitson.