Catching COVID more than once: What we know about reinfections

Since the emergence of the Omicron variant of the coronavirus, cases of COVID reinfections are becoming more common.

People wearing protective masks to help curb the spread of the coronavirus
People wearing protective masks to help curb the spread of the coronavirus wait for a traffic light at an intersection in Tokyo [File: Eugene Hoshiko/AP Photo]

As the Omicron variant of the coronavirus drives new waves of COVID infections around the world, some early studies appear to show the risk of reinfection has risen.

According to an analysis by the United Kingdom’s Office for National Statistics (ONS), the risk of reinfection is 16 times higher when Omicron was the dominant variant, compared with the period when Delta was dominant.

The analysis also showed that unvaccinated people were twice as likely to be reinfected than those who had their second dose of vaccine in the previous 14 to 89 days.

With infection rates continuing to surge across most regions around the world and as the number of reinfections also climbs, experts have said that protection from previous infections or vaccines declines over time.

What is a reinfection?

A reinfection is a medical condition that usually occurs when a person becomes infected with COVID-19, recovers, and then gets infected again. It could happen with any of the variants of the coronavirus.

According to the United States Centers for Disease Control and Prevention (CDC), a reinfection is considered such if the patient “tests positive again 90 days or more after their first positive test”. The same standard has been established by the UK Health Security Agency (UKHSA).

The 90-day period has been chosen because some patients continue to have the virus in their systems for longer than the average of about two weeks, making it difficult to distinguish between an infection or a reinfection within this time frame.

“The majority of patients with normal immunity do not have the virus beyond 10-14 days, but some harbour it for a longer time and therefore the time has been extended to three months,” Dr Pere Domingo, currently senior consultant and HIV/AIDS programme director at the Infectious Diseases Unit of the Hospital de la Santa Creu i Sant Pau, told Al Jazeera.

Is this risk of COVID reinfection rising?

According to a report published by the UK’s ONS in June 2021, reinfections were considered rare, but the rate of reinfections has increased since the Omicron variant became the dominant strain in late 2021.

An analysis published last week by the news agency Reuters, citing data collected by the UKHSA, suggested that suspected reinfections accounted for approximately 10 percent of confirmed cases in England in January. Suspected reinfections made up fewer than 2 percent of cases in the six months prior to December 6. A total of 588,000 possible reinfections have been registered in England.

Meanwhile in Italy, 3 percent of the new cases were reinfections, up from about 1.5 percent before Omicron, a spokesperson for Italy’s National Institute of Health said last week.

Dr Domingo noted that the Omicron variant has mutated significantly compared with other variants, meaning that protection developed against previous variants could be less effective against Omicron.

“Omicron has mutated many times,” Dr Domingo said. “These mutations have changed the antigens, the proteins are no longer the same as they were in Delta, nor the strain that came out in Wuhan.

“Therefore, the antibodies that one could develop against the original strain or against Delta, are no longer useful for Omicron,” he added.

According to the research by Imperial College London, the protection afforded by the past infection may be “as low as 19 percent”.

Why are cases of reinfections rising?

Viruses are constantly evolving and these changes naturally lead to the emergence of new strains that can lead to new infections.

“There is always a struggle between the forces of the individual and immunity on the one hand and the virus on the other,” Dr Domingo said.

“And the way the virus fights is by changing, by making mutations that will allow it to avoid the patient’s antibodies,” he added.

According to research from South Africa, people infected with Omicron developed an antibody response to the current and previous strains. However, according to the Gavi vaccine alliance, the immunity from a Delta infection provides limited protection against Omicron.

Previous infections or vaccines will provide protection, and the greater the exposure to the virus leads to greater protection, but the “immunity is not complete and it declines over time,” Dr Domingo said.

“And if the virus changes, the protection generated by infection, is overwhelmed.”

Are reinfections less severe?

According to early research, reinfections are generally mild. A study done in the state of Qatar found that reinfections “have 90 percent lower odds of resulting in hospitalisation or death than primary infections”.

Dr William Schaffner, professor of medicine at Vanderbilt University Medical Center, said the severity of a reinfetion depends on the patient’s immune system.

“If you are immuno-compromised, or if you are a person who is frail, or sick, then I would think a second infection could potentially be serious enough to put you in the hospital, but if you have a normal immune system, the second infection is not likely to be severe,” he added.

Experts said a reinfection would provide some level of immunity against any potential reinfection in the future, but the best immunity is the result of a hybrid immunity.

Hybrid immunity is the result of having been both infected and vaccinated against the virus. According to research, this could generate a “super-immune” response.

However, there is a risk in the long term effects of the infection.

“Anyone who recovers from COVID stands or risk of developing so-called Long COVID,” Dr Schaffner said.

“[And so far] we have no information, on whether second infections are more likely to result in Long COVID than first infections,” he added.

How can the rate of reinfections be slowed?

Experts have said the current guidance in place to combat COVID-19 are still effective. The World Health Organization (WHO) has recommended people get vaccinated.

It also advised people to maintain physical distance, avoid crowds and close contacts, wear a properly fitted mask, clean your hands frequently, and cover your mouth and nose when coughing or sneezing.

“We need people to keep [following] all these measures,” Dr Ali Fattom said.

“Precautions are very important, not only for the person itself, but you don’t want to transmit the virus to others and put them at risk,” he added.

Source: Al Jazeera