In the last two weeks, 20,890 infections were reported, according to the latest data from Spain’s state-backed Carlos III Health Institute (ISCIII). The data includes confirmed and suspected repeat infections.

This is higher than the 17,140 cases of repeat infection registered from the start of the pandemic to December 22nd.

The reinfections were due to the highly contagious Omicron variant, immunology professor Alfredo Corell told Spanish news site NIUS.

“Prior to this variant, reinfections were anecdotal at the global level. They were people who had lost their protection or were immunosuppressed. Omicron has changed this paradigm. We cannot say that there are no reinfections now – there are many,” he explained. 

The findings reinforce a December report from the UK’s Imperial College, which said that people were over five times more likely to get reinfected with Omicron than with Delta.  

Fortunately, reinfections are “rarely serious,” according to Julian Olalla, doctor and spokesperson for the Spanish Society of Infectious Diseases and Clinical Microbiology, adding there were currently no hospitalisations for cases of repeat infection.

“I haven’t seen any for a long time,” he added.

The most likely reason for the higher number of reinfections with Omicron is the more-than-40 mutations that the variant has in its spike protein, Corell said, explaining that this made it easier for the virus to evade the body’s antibodies.

But the body also has cellular immunity, which resists mutations better. Although this type of immunity won’t stop people becoming reinfected as it takes a few days to become active, it does prevent most serious disease, he explained.