What are the odds of catching COVID-19 twice? Here’s what we know about reinfection

In January, a 31-year-old woman in Spain tested positive for COVID-19 after developing a cough, fever, and feeling generally unwell.

On the face of it, it sounds fairly unremarkable — except for one detail.

The healthcare worker, who was fully vaccinated and boosted, had tested positive for COVID-19 just 20 days before.

The woman’s first infection was picked up via routine COVID-19 screening at her workplace.

She didn’t develop any symptoms, and isolated for 10 days before returning to work.

But when she began feeling unwell a few weeks later, she tested again.

This time, genome sequencing revealed she had contracted Omicron — after catching Delta in December.

Scientists recently reported the case as the shortest-known interval between COVID-19 infections.

“People who have had COVID-19 cannot assume they are protected against reinfection, even if they have been fully vaccinated,” said Dr Gemma Recio of the Institut Català de la Salut in Tarragona and one of the study’s authors.

While a 20-day gap between infections is particularly short — and likely unusual — COVID-19 reinfections are increasingly common.

So, what are the odds of getting sick with COVID more than once?

Reinfections on the rise with Omicron

Health authorities typically define a reinfection as a case 90 days or more after a previous COVID infection, to exclude people who simply shed the virus for a long period of time.

In Australia, a growing number of people have reported catching COVID-19 twice, but it’s difficult to know exactly how common it is because publicly available data is limited.

In Victoria, one of the few jurisdictions that has reported this data, almost 10,000 COVID-19 reinfections were recorded in the three months to March 2022.

The good news is that COVID reinfections are likely to be less severe than primary infections.(ABC News: Keane Bourke)

But overseas, in countries with previously high rates of infection, data shows COVID-19 reinfections have increased significantly since the arrival of the highly-transmissible Omicron variant in late 2021.

In England, for example, more than 890,000 people have been infected with COVID-19 more than onceand most reinfections have occurred since December.

“If you go back to last year, [UK authorities] were estimating about 1 percent of COVID cases were reinfections,” said epidemiologist Hassan Vally of Deakin University.

“Now, they think that’s up at around 10 percent.”

Many of these cases are likely to be people who were infected by the Alpha or Delta variants in 2021, and then infected again by the Omicron BA.1 subvariant or its even more transmissible cousin, BA.2.

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