The number of Covid reinfections reported in Spain in the past fortnight has exceeded the total number of repeat infections documented during the rest of the pandemic, according to the latest data from Spanish researchers.
In the span of two weeks in late December and early January, 20,890 reinfections were reported in Spain, figures from the state-backed Carlos III Health Institute suggested.
While the bulk of cases appeared to be mild, the number is higher than the 17,140 cases of reinfection documented from the start of the pandemic to 22 December. The Spanish data includes both confirmed and suspected reinfections.
Researchers attributed the growing number of repeat infections to the fast-spreading Omicron variant. “Prior to this variant, reinfections were anecdotal at the global level,” the immunologist Prof Alfredo Corell, from the University of Valladolid, told the Spanish news site Nius. “Omicron has changed this paradigm.”
The Spanish data adds to previous research that has linked Omicron to an increase in reinfections. A report released by researchers at Imperial College London in mid-December estimated the risk of reinfection with Omicron to be 5.4 times greater than with Delta.
“This study provides further evidence of the very substantial extent to which Omicron can evade prior immunity given by both infection or vaccination,” the study lead, Prof Neil Ferguson, said in a statement at the time.
The report, modelled on people who tested positive in England in late November and early December, added impetus to a call by scientists to include reinfections in UK Covid figures.
In South Africa, where the Omicron variant was first identified, preliminary research suggested the variant appears to be reinfecting people at three times the rate of previous strains.
“Previous infection used to protect against Delta but now, with Omicron, that doesn’t seem to be the case,” said Prof Anne von Gottberg, from South Africa’s National Institute for Communicable Diseases, in early December.
The findings from the UK and South Africa were echoed online by the World Health Organization in late December. “Individuals who have recovered from Covid-19 are three to five times more likely to be reinfected with Omicron compared with Delta,” it said in an update on Covid-19.
A limited study in the United States suggested that those who are reinfected with Omicron may experience fewer and milder symptoms compared with infections from previous strains of the virus. The study, published by the US Centers for Disease Control and Prevention, looked at a cluster of Omicron cases in a family of six in Nebraska and found that the five reinfections were reported to be less severe than previous bouts of the virus.
In Spain, the researchers pointed to several factors that may explain the rising number of reinfections. “Either the virus mutates or a person’s immunity wanes,” said Dr Pere Domingo, the Covid coordinator at Barcelona’s Santa Creu i Sant Pau hospital, in comments to El País. “In this wave, we’ve seen both factors at play.”
Others suggested that the potential for reinfection was magnified given the large number of Covid-19 cases being reported. “Even if the possibility of reinfection is small – say, one out of 100 – if there are millions of infections, the reinfections will be in the tens of thousands,” Prof José Antonio López Guerrero, of Madrid’s Autonomous University, told Nius.
Recent weeks have seen the number of Covid cases in Spain rise to record highs, pushing the 14-day infection rate to 2,723 cases per 100,000, according to the latest figures from the health ministry. To date, the sharp rise in cases has not resulted in a surge of hospitalisations; the number of patients in intensive care units is about half that of the figure from a year earlier.
Spain’s prime minister, Pedro Sánchez, said last month he was confident that the country’s high vaccination rate – hovering at about 80% of the population – would translate into a milder wave as the country grapples with the Omicron variant. “We are obviously going to see high numbers of infections, but not hospitalisations and ICU admissions compared to previous waves,” he told reporters.
