Should we fear reinfections with COVID-19?

Since the Omicron variant emerged, the number of people getting a new SARS-CoV-2 infection has been steadily increasing. What causes these reinfections? How often can they occur? Do they increase the risk of long-term sequelae? Here is what epidemiological observations indicate.

Reinfections seem to be becoming more and more common. Is this really the case?

Prior to the introduction of Omicron, reinfections were rare and accounted for no more than 1% of all infections. The arrival of the variant in the country changed the situation. Last January, as the Omicron wave gained momentum, their number increased tenfold, reaching 10% of infections in Quebec. Currently, this proportion is around 20%. “It is not a complete portrait of what is happening in the general population [québécoise], because we no longer test everyone. It is our data among health care workers, who are tested more diligently, that allow us to see that, indeed, there is an increase in the proportion of infections that are reinfections”, specifies Dr. Éric Litvak, vice- Associate President for Scientific Affairs at the National Institute of Public Health of Quebec.

What are the causes of these reinfections?

Two phenomena explain the occurrence of these reinfections.

First, the immunity induced by vaccination and coronavirus infections (a large family of viruses responsible for certain colds, but also for COVID-19) does not last very long, unlike that conferred by other infectious diseases that can persist for several years, or even for life, underlines the D^r Litvak. “We see that antibodies gradually disappear after vaccination or infection, particularly neutralizing antibodies, which need to be present in large numbers to stop the virus quickly,” said Dr.^D Caroline Quach, microbiologist-infectiologist at CHU Sainte-Justine.

The other thing is that the COVID-19 virus, SARS-CoV-2, is changing very quickly. And the mutations it undergoes often target its spicules, these spines with which it attaches to our cells to infect them. However, the antibodies that are generated following vaccination (which was designed against the ancestral strain) or a first infection no longer bind as well to the modified spicules of the new variant; they are therefore less effective in their attempts to prevent the virus from attaching to our cells.

Can we be reinfected by the same variant or sub-variant?

To answer this question categorically, it would have been necessary to sequence the samples taken during the successive infections experienced by the same person. For each case of reinfection, one can only infer which variants are responsible for the first and second infection “from what we know about the variants that are circulating,” says Dr. Litvak.

“It is possible to be reinfected by the same variant after a certain time. Cases were documented early in the pandemic, when the same variant circulated for a long time. But that’s not common,” he says.

Experts agree, however, that at this time, reinfections are largely attributable to a variant or subvariant different from the one that caused the first infection, because the new mutations it has allow it to escape the immunity acquired in the past.

Moreover, recent studies have demonstrated that people who have been infected with Omicron’s BA.1 subvariant have produced abundant antibodies allowing them to later cope with this same subvariant and the variants that have circulated. previously. But these antibodies proved ineffective in countering the variants that appeared later, such as BA.4, BA.2.12.1 or even BA.5, which is all the rage at the moment. “These studies suggest that the immunity we gain during an infection protects us against this variant and the previous ones, but not against future variants”, summarizes the D^r Donald Vinh, microbiologist-infectiologist at the MUHC.

“Right now, variants other than BA.5 are circulating: in particular the BA.2.75 sub-variant, which appeared in India and reached the Netherlands, as well as BE.1 and BG.2, which were detected in Quebec. However, we do not yet know if an infection with BA.5 will protect us against these other variants on which we have very little information at the moment,” he warns.

How long are we protected against reinfections?

In the majority of cases, reinfections occur three months or more after the first infection. A few cases were observed within two months. “In people who believe they have been reinfected two to three weeks after their first infection, it would rather be remnants of their previous infection that would manifest themselves,” says Dr.^D Quach.

“In the acute phase of the infection, we have all the weapons of our immune system in motion. It will be very difficult for any virus to break through this antiviral defense which is in full swing. During the first two to three weeks of infection, it is therefore very difficult to be re-infected, but when things calm down, immunity begins to wane and, over time, you can be re-infected if you encounter a new varying”, explains the D^r Vinh.

The duration of this protection depends on the immunity profile of the person, specifies the D^r Litvak. “When was the person infected? By what variant? How many doses of vaccine did she receive? When did she receive them? All these parameters modulate the duration of protection and the risk of reinfection. But generally, it remains quite high during the first two months, and then it gradually decreases according to the profile we have,” he says.

Does being vaccinated reduce the risk of reinfection?

“What protects us the most is combined or hybrid immunity. People who have been vaccinated (with at least two doses) and who have had an infection have the best protection and the one that lasts the longest,” says Dr.^r Litvak.

Do reinfections increase the risk of long-term sequelae?

Reinfections usually cause less severe symptoms than the first infection. But a large study that has yet to be peer-reviewed warns of the risks associated with multiple reinfections. This study indicates that each reinfection increases the risk of mortality, hospitalization and pulmonary, cardiovascular, renal, neurological, gastrointestinal and psychiatric sequelae, in particular. As the study only involved American veterans (the vast majority of them elderly men), these conclusions probably do not apply to the general population, but are mainly aimed at the elderly, immunocompromised and with health problems. pre-existing. They nevertheless invite caution and take measures to avoid being reinfected.

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