Health authorities say people infected with SARS-CoV-2 are protected for 90 days. But experts warn that one should not assume that a person has been immune for a long time and that re -infections are possible before three months.
Re-infections are not a new phenomenon, recalls from the beginning Catherine Hankins, professor of public health and population health at McGill University and co-chair of the Task Force on Immunity to COVID-19. We have known since the early days that this pandemic exists, but it is relatively rare, especially when the viruses re -infected are identical.
However, the advent of Omicron increases the number of re -infections. According to the latest data from the UK, the risk of re -infection is 10 times higher than during the waves caused by the Delta.
Alain Lamarre, professor-researcher who specializes in immune response and virology at the National Institute for Scientific Research (INRS), pointed out that Omicron’s genetic diversity makes it easier to escape immunity conferred by infection or vaccination.
It is unclear whether the 90-day period still remains in the case of the subvariant of BA.2, which makes up 75% of COVID-19 cases in the country. Moreover, the latest report (New window) on reinfections of the National Institute of Public Health of Quebec (INSPQ) determines that it is too early to make conclusions. It’s still a relatively new variant and we still don’t understand everythingrecollection of Mr. Lamarre.
In addition, the massive volume of infections in recent months is likely to be contributing to the increasing number of re-infections, Mr. Lamarre believes.
” The more cases there are, the more likely we are to get an infection and get an infection again. “
In the UK, the latest data (New window) show that by mid -April, nearly 12% of cases were re -infected. Of the 900,000 cases of re-infection documented in the UK since the pandemic began, just over 10,000 people have been re-infected three times and only 100 have been re-infected four times.
Public health in France (New window) SARS-CoV-2 re-infections are already considered are unusual events, especially in a context of high circulation of the Omicron variant. More than 650,000 cases of SARS-CoV-2 reinfection have been identified since December 6, 2021 in France. From March 13 to 22, 5.4% of all cases were reinfections.
France does not count reinfections that occur for less than 60 days, but indicates that they bihira. From the beginning of December, 8.4% of re -infections occurred between 60 and 89 days after the first infection; 5% between 90 and 119 days; 18.6% between 120 and 179 days; 59.9% between 180 and 364 days and 8.1% for 365 days or more.
In Quebec, the latest report fromINSPQ (New window) indicates that there were approximately 8,800 re-infections between November 28, 2021 and November 1eh January 2022, i.e., approximately 5% of cases identified during this period. Approximately 16% of these reinfections occurred less than 150 days before the initial infection.
Note that the number of tests is greatly restricted, which has an influence on the confirmed number of infections and re -infections. This is for the same reason that theINSPQ no longer providing new data on re -infections.
Why are we talking about 90 days?
This 90-day period was established by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) in the USA. Generally, an infection, after 90 days, is not diagnosedsaid Mr. Lamarre.
He explained that, in the first 90 days after an infection, it is difficult to know if the infection is actually a reinfection.
Because the removal of SARS-CoV-2 can take several weeks, it can be complicated to know if it is a chronic infection, a first-stage reactivation or a reinfection, and more.INSPQ.
[L’infection] may vary over time. The virus can pass from the throat and then go to the lungs. The infection can have waves or stages in which one is more or less symptomatic. It’s hard to rely on symptoms alonehe says.
Within three months, the sample should be sequenced to determine if they are two different viruses. However, most people do not have access to this data. Thus, it is often difficult to know whether one has been reinfected or not.
This is why most countries use the 90-day period to define re-infection and do not count infections that occur less than three months after the initial infection.
So does protection after infection last at least 90 days?
Recently, researchers in Spain discovered the case of a patient who was re -infected within 20 days. So far, this case seems like an exception, but as data in the UK and French show, it is possible to re -infect before 90 days.
So is a person protected for 90 days after infection? In fact, the answer is complex and it’s hard to say that everyone infected has 90 days of protection.
Jane Heffernan, a disease modeling expert at York University who studies the immune response of the vaccine against COVID-19 through mathematical models, added that there are many factors that influence each individual’s level of immunity. and may explain why we see so many cases of reinfection.
” It depends on age, comorbidities, time since last dose, type of vaccine, etc. “
For example, older people are more at risk of re -infection, according to data from the UK (New window). In fact, the risk of reinfection drops by 6% for every 10 years of age.
Mrs. added that. Heffernan Early infections with no symptoms or with few symptoms do not provide long -term immunity.
According to CDC and the INSPQ (New window)people with low viral load or asymptomatic in the first infection have high viral load in the second stage, suggesting that there was a weak immune response to the first infection.
This is why Mr. Lamarre and Ms. Hankins and Ms. Heffernan that the population should be aware of the risk of re -infection, and sometimes within 90 days.
Is an infection equal to one dose?
No, say three experts. An infection improves a person’s immunity, but it is often short -lived. The vaccine remains the best protection, Hankins said.
People who are not vaccinated and then become infected do not develop an adequate immune response to prevent reinfection, according to a recent study. (New window) from Denmark, which has not yet been peer reviewed.
According to the UK government, people who were not vaccinated were twice as likely to be re -infected, compared to people who received two doses.
According to the INSPQ analysis (New window) published on April 21, an initial infection, even without vaccination, reduces the risk of infection with the Omicron variant by 44% and reduces the risk of hospitalization by 81%. On the other hand, the protection afforded by a previous infection increases significantly with each additional dose of vaccine.
It should be noted that in people who have not been vaccinated, protection against reinfection decreases rapidly. This is from 66% after three months, then to less than 50% after 6 months and less than 30% after 12 months.
In comparison, in someone who is infected and vaccinated with one or two doses, protection against re -infection goes from about 80% to more than 60% after two months, then remains stable for up to 12 months.
In a person who has been vaccinated three times, this protection remains at 80% for 2 to 5 months (impossible to say for a longer period, since the third dose is not available for six months).
It should be noted that this review ofINSPQ does not offer data showing how well BA.1 infection protects against BA.2 infection.
One thing is certain, people with one infection and three doses have hybrid immunity, Lamarre said, adding that immunity is more consistent with vaccination.
" This is the best form of immunity. Vaccination provides a relatively homogeneous immunity from one person to another, which is not the case with an infection. "
“Three months is still a good size, but you shouldn’t rely on an infection to think you’re safe. ad vitam aeternam. Feel free to get vaccinated after your infection, says Alain Lamarre.
The Committee on Immunization of Quebec (CIQ) recommends that infected people receive their booster dose three months after infection, but that these people will receive it as soon as their symptoms end [...] and when their period of separation was over.
Source: Radio-Canada
