Sixth wave begins to subside in Catalonia

Despite having reached peak in infections, effect of stealth variant now being closely monitored

4 min
A long line of people waiting to get the covid -19 booster vaccine.

Santa Coloma de GramenetInfections have peaked and after weeks of "slowing down", Catalonia is finally beginning to get over the most uncertain wave of covid. In the week of January 17 to 23 more than 250,000 positive cases were detected due to the rapid transmission of the virus, which mainly affected younger age groups. This is reflected in the official records thanks to the diagnostic effort in the educational environment and self-diagnosed cases in pharmacies. "The data is very clear: we have got passed the peak and this week there is already a fairly rapid drop in cases," summarises Clara Prats, a researcher in the Biocom-SC group at the UPC.

Mathematical models suggest that covid cases will decrease every week by between 15% and 20% and the drop is more evident in younger age groups. "They have the highest incidence but they will also decrease faster than the rest," Prats explains. Although it is possible that real incidence is much higher due to asymptomatic patients, since January 23 the 15-29 age group has recorded fewer infections (from 3,000 cases per 100,000 inhabitants to 2,400 in one week), and the same has happened with the 30-49 age group (from 3,400 to 2,895). Minors, who have undergone three times as many diagnostic tests as the rest of the population since the start of the second school term, have already reached their own peak, as anticipated by the Education Department last week, with nearly 7,000 cases per 100,000 inhabitants. The rate is now 5,400.

The first indicators that show the pandemic beginning to buckle is the rate of infections detected in symptomatic people and the number of covid-related consultation in health centres. On January 15, the peak in positive antigen tests among people with symptoms was reached (10,000 cases were identified in a single day, half of the tests performed), a positivity figure that is now falling progressively and already stands at 40%. Two days later, on January 17, CAPs made 102,500 consultations in just 24 hours, the highest figure in the entire pandemic. Now, on the other hand, they make half that number, about 50,000 visits per day.

Another key indicator is the rate of contagion or Rt – which indicates that the virus enters the control phase when the value is under 1 – since it has dropped from 1.16 to 0.87 in just one week. "But if you correct for weekend reporting biases, the Rt is already between 0.7 and 0.8. This is good," explains Prats. According to the expert, the case curve in Catalonia will continue to fall and no "surprises" are expected in the short term, although it is possible that in a couple of weeks the reduction will be slower due to two factors.

Omicron alters the hospital pattern

The first factor is the lifting of almost all restrictions, which could slow the decline but would have no ability to stop or reverse it. The other factor that could stall the descent of the curve would be the effect of the stealth variant (BA.2), the Omicron subvariant that has already been detected in Catalonia and whose rise has coincided with a stagnation of epidemiological improvements in countries where it is most prevalent, such as the United Kingdom. "This makes us think that perhaps incidence will drop at a good pace for a few weeks, but then it will also slow down," warns Prats, who, however, stresses that if this scenario is fulfilled, cases will have already dropped quite a lot.

In fact, the new variants (the original Omicron and its BA.2 mutation) have altered the rules of the game and it is increasingly complicated to make predictions or interpret the data. For example, the first consequence of reaching the peak number of cases has been a stagnation in the number of patients in intensive care. Whereas until now the beds in critical care areas were the last to empty when a wave was over, in this case admissions have slowed down early and the number of patients has stabilised at around 460. Although the Health Department has made changes in the registration of patients in ICU – the reason for admission is now specified in order to distinguish patients admitted due to complications caused by covid from those admitted due to another pathology who moreover have covid – this change in trend is prior to the modification of the criteria.

On the other hand, and unlike other waves, hospitalisations on the ward have not slowed down like those in intensive care and, in fact, the influx of patients has not stopped. This Monday, in the absence of discharges, the threshold of 3,000 admissions has been exceeded (there are now 3,042, 188 more than on Friday) but the rate is lower than in previous weeks. "The fact that Omicron is milder and that large swathes of the population are vaccinated or have natural immunity means that the pressure on care, despite being high, has stabilised," says Prats. According to the researcher, replacing the delta variant with the Omicron reduces the risk of hospitalisation of a 70-year-old person by three and a half times. If this person is vaccinated, the risk of becoming seriously ill drops from 7.5% to 1.5% and, if they have also received a booster dose, the chances drop to 0.25%

"These are good prospects but please let's get vaccinated to protect against severe disease. The circulation of the virus is still very high," recommends Biocom, which notes that deaths have also decreased. While 285 fatalities were reported during the week of January 14-20, in the last week the number dropped to 238 deaths. While the number is high, it is unrelated to the explosion in contagions. Most of this week's victims (198) were over 70 years of age, as this virus is particularly harmful for the elderly.