The incidence rate of coronavirus cases in Spain has fallen for the first time since the current sixth wave began to rise, two and a half months ago. According to the latest Health Ministry report, the 14-day cumulative number fell 91 points on Tuesday to 3,306 cases per 100,000 inhabitants. Time will tell whether this is a one-off fall or the start of a downward trend indicating the end of the sixth coronavirus wave.
Experts warn that it is difficult to accurately analyze the daily figures, as the data is incomplete and how it is collected varies between the regions, which are in charge of their healthcare systems, Covid-19 vaccination drive and coronavirus restrictions.
After an unprecedented explosion of infections over Christmas, Spain saw a clear slowdown in the epidemiological curve last week: contagions continued to rise, but on a slower scale. This suggested that a change in trend was imminent, in line with experts’ predictions that the wave would peak in mid-January.
The problem when it comes to interpreting Tuesday’s figures is that the official statistics on daily coronavirus cases do not accurately reflect the true spread of the coronavirus. The first issue is that many people are using home antigen kits to confirm their infections, and these contagions are not always reported to authorities. What’s more, if they are reported, they may not be included in the official statistics – the regions of Madrid and Andalusia, for example, do not count these contagions in their figures. The second problem is delays in notification due to the pressure on primary healthcare centers which may take more than a week to attend to a person who has early symptoms.
Due to these issues, the data reported by the regions to the central Health Ministry is an approximation that indicates the overall trend, but is not an exact reflection of what is happening in reality. But there are other statistics that support the reported fall in transmission rates. In Navarre, which is one of the regions that is carrying out the most testing, the cumulative incidence rate has fallen by more than 2,000 points in seven days – a clear sign of a change in trend that appears to be happening in the rest of Spain as well.
But Clara Prats, a researcher in computational biology at the Polytechnic University of Catalonia (UPC), warns that it is important not to preemptively announce the peak of the sixth wave. “It is going to be harder to situate in space and time,” she says. “When it [the incidence rate] has been falling for some more days it will be clear that we are not seeing artifacts [signs that alter the statistics], but the way of measuring we have now makes it very difficult to interpret the odd rises and falls of a specific day.”
Ildefonso Hernández, from the Spanish Society of Public Health (Sespas), believes the incidence rate in Spain now is noteworthy because it is so high, but says the parameter stopped being the best way to measure the evolution of the pandemic some time ago. The best approach is to reach conclusions using several data points.
The way of measuring we have now makes it very difficult to interpret the odd rises and falls of a specific dayClara Prats, researcher at the Polytechnic University of Catalonia
Both experts, for example, are closely following hospitalizations for Covid-19. Admissions continue to rise and, in theory, will continue to do so for a few days after the peak is reached. But interestingly, the number of Covid-19 patients in intensive care units (ICUs) has stopped rising. On Tuesday, the figure actually dropped to 2,243 – a fall of nine since Monday.
Prats explains that ICU admissions, which started to increase a few weeks after the number of infections began to rise, are no longer following this pattern. According to the expert, this is because the sixth wave involved two coronavirus variants: delta and omicron. Initially, delta, which causes more serious illness, led to a spike in critical Covid-19 cases. The strain was then replaced by omicron, which causes more minor cases, and this seems to have led to a stabilization in the number of ICU admissions, something which has also been seen in Denmark and the United Kingdom.
To determine whether the sixth wave is on a downward trend, more time must pass, perhaps even weeks. “With the notification [of cases] we have today, which does not allow you to go into detail on a daily basis, it is more interesting to look at weekly trends, the number of tests being done, the positivity rate [the percentage of tests that come back positive out of the total],” says Fernando Rodríguez Artalejo, a professor of public health at Madrid’s Autonomous University.
The last data point to indicate a change in trend is the number of fatalities. This parameter also tends to take longer to fall once cases and hospitalizations have started to drop. On Tuesday, the Health Ministry added 284 deaths to the official toll. This figure represents the number of fatalities that were reported on the previous day – not the actual date of death. Once notified, each fatality must be then ordered according to the date of death, which could be days or even weeks earlier.
Spain now has a more accurate – although not exact – picture of the deaths that took place two weeks ago, when around 100 fatalities were being recorded every day. Delays in notification mean the curve in fatalities cannot be seen in real-time. That said, it is likely that this indicator will take more days to clearly fall once a drop in infections is detected.