The question of reinfection has arisen since the start of the Covid-19 pandemic. It is indeed difficult to know if the fact of having been infected with SARS-COV-2 implies that we are immune : if the antibodies have developed well, they are not necessarily neutralizing (capable of preventing the development of the disease). Thus, the presence of antibodies testifies to the fact that the organism has been in contact with the virus, without being certain that it offers protection against a new infection. And even in the presence of neutralizing antibodies, it is difficult to say how long the immunity provided will persist.
Rare re-infections, which do exist
In the current state of knowledge, scientists agree that the reinfection phenomenon remains rare, but a study by researchers at Imperial College London indicates it is not as rare as they might think.
Published in February in the Journal of Infection, their results come from an analysis of 33 recurrent Covid-19 cases in Brazil confirmed by PCR test, after a disease-free period following the first infection. Researchers say that a acquired natural immunityagainst SARS-CoV-2 does not guarantee complete protection against subsequent infection. Underlying biological factors were also found: 42% of cases had a blood group A +. In addition, analysis of anti-SARS-CoV-2 antibodies for 17 of these cases showed a weaker antibody response after the first infection compared to the control group. Recurrence of infection therefore tended to be more serious.
“This is the largest case series to date that provides evidence to suggest that people who produce a weak antibody response to SARS-CoV-2 may be more likely to be re-infected with the virus. in the future.
Our results could be important when examining herd immunity thresholds and levels of naturally acquired protection against the virus, ”explains Prof. Danny Altmann.
More frequent re-infections in people over 65
Researchers of the Statens Serum Institut (Copenhagen) are also among those who study this phenomenon. Their study published in March 2021 in The Lancet was based on the 10 million PCR tests carried out last year in Denmark: four million Danes have done at least one test. The researchers analyzed the data, focusing on people who tested positive more than once. Their results show thatprevious infection with Covid-19 protects most people from re-infection.
Among those who tested positive in the first wave, 0.65% of them tested positive again during the second wave. In comparison, 3.3% of those who tested negative in the first wave tested positive in the second wave. “Those who had not tested positive before were therefore about five times more likely to test positive later. 80.5% degree of protection against subsequent infection “, explain the researchers. There was no difference in protection between the two sexes, nor between the first part and the last part of the total period of the study. In other words, “there was no indication that protection had started to decline after six months,” notes the scientific team.
However, dividing the population by age groups, a different trend emerged for the elderly because among those over 65, the protection was estimated at only 47%. Which indicates that they are more likely to catch Covid-19 again: people over 65 would be more at risk of reinfection with only 47% protection against repeated infection, compared to 80% for younger people. A finding that highlights the importance of measures such as social distancing and prioritization of vaccines.
“Our study suggests that most people will be protected against a new infection for at least six months. But not everyone is protected and especially in the elderly, alone. about half of it seems to be protected after a first infection “, explains Prof. Steen Ethelberg who conducted the study.
“Even if you have already been infected, our results suggest that it is advisable to continue to follow the advice on how to protect yourself from infection. Additionally, the results highlight the need for vaccination for everyone because natural protection, especially in the elderly, cannot be invoked “.
To note that the study took into account the “classic” Covid-19 strain and not the variants.
According to a study published on August 12, 2020 in the journal The Lancet Infectious Diseases by a team of American researchers, the cases of reinfection could be explained by:
- the fact that the patients have been exposed to very high dose of virus the second time ;
- the fact that the patients have been exposed to a more virulent strain of the virus (coronavirus variants);
- the presence of antibodies due to the first infection (as can be the case with dengue).
It is not necessarily a re-infection with the coronavirus
When an apparently “cured” patient presents symptoms of the coronavirus, it is not necessarily a question of reinfection. Several elements could lead to confusion:
- a failure of screening tests ;
- the possibility that samples were poorly preserved ;
- or that the insufficient viral load to be detected.
But according to the most probable hypothesis, the patients in question would suffer from prolonged coronavirus infection, not from reinfection. In other words, the virus would still be present in their body, in the form of undetectable traces, and could be “reactivated”, due to a secondary disease for example. But the precautionary principle is in order.
Immunity against covid-19: what do we know about the lifespan of antibodies?
In theory, a person already infected with a virus is immune to it. When our body comes into contact with a virus, it develops specific antibodies capable of recognizing and combating said virus more effectively when they are faced with it again. The first studies of the lifespan of antibodies assumed a relatively short period of immunity. A study conducted in May 2020 by the Institut Pasteur with 160 caregivers working at Strasbourg University Hospitals and affected by a minor form of the disease, indicated that “the levels of antibodies are, in most cases, compatible with protection against a new infection with SARS-CoV-2, at least up to 40 days after the onset of symptoms “.
8-month protection according to new studies
A study published on February 5, 2021 in the review Science believes that the immune memory persists for up to eight months after infection with the coronavirus. 188 patients with asymptomatic, moderate and severe symptoms of the disease were followed for eight months (80 men and 108 women). Verdict? The neutralizing antibodies (which prevent the coronavirus from infecting cells) persisted beyond six months: 90% of participants were still HIV positive when tested between six and eight months.
Study supports idea that natural immunity to SARS-CoV-2 is long lasting
One of the key questions to better predict the evolution of the COVID-19 pandemic is the duration of natural immunity. A growing number of studies suggest that most people generate a humoral (antibody) and cellular (T cell) response that lasts for months or even years. By exploring in more detail the evolution of the immune response in the months following infection with SARS-CoV-2, researchers from the Barcelona Institute for Global Health (ISGlobal) are optimistic on this subject. This tells them that a year after infection, most people keep anti-Spike antibodies regardless of the severity of their symptoms.
Results published in BMC Medicine are important because they “suggest that immunity generated by the vaccine will also be of long duration ”, estimates the scientific team. During the first wave of the pandemic, it began a follow-up study of a cohort of healthcare workers with COVID-19. A total of 173 people working in health centers in Catalonia and most of whose infections were mild to moderate, although some cases required hospitalization. The research team took regular blood samples from them starting in September 2020 to measure the level and type specific antibodies to SARS-CoV-2.
“The results obtained so far lead us to believe that immunity to SARS-CoV-2 will last longer than we initially thought. Being a new virus, it is very important to understand how it behaves and affects different people, ”says Anna Ruiz Comellas, co-author of the study. Researchers were interested in different types of antibodies or immunoglobulins (Ig) sent by B lymphocytes to defend the body during infection: IgG, IgM and IgA. The study notes that no significant decrease antibody levels was observed during the first five months of follow-up, and at nine months 92.4% of people remained seropositive.
Specifically, 90% of the participants had IgG in their blood, 76% of IgA and 61% of directed IgM against the “S” or Spike protein. As Inserm explains on this subject, “the Spike protein is the key that allows SARS-CoV-2 to enter our cells. It is also one of the targets of our immune system in the face of infection, and that of vaccines currently in development. It is therefore crucial to characterize it as finely as possible. ” “These data confirm that IgGs last longer but IgM levels, that are supposed to last less have surprisingly received enough support over time. ”, Adds Gemma Moncunill, co-lead author of the study.
In addition, it turns out that having been hospitalized, having had a fever and loss of smell and taste were associated with higher antibody levels at five or nine months. Four re-infections were observed among the participants. Two of them were symptomatic and occurred in seronegative individuals while another asymptomatic reinfection occurred in a subject with very low levels of antibodies. Which suggests, the researchers conclude, that anti-Spike antibodies appear to protect against symptomatic infections, but also that people who have not been previously infected should be given priority for vaccination because those who have already been infected can be protected for at least a year.
Women would be immune longer than men
A team of researchers from Strasbourg recently looked at the evolution of the immune response in the months following an infection with SARS-CoV-2. Their conclusions, reported by the National Institute for Health and Medical Research (Inserm) in a communicated published on April 12, 2021, indicate that women develop a more stable antibody level than their male counterparts.
“The researchers generally observed that women had more effective immune protection than that of men,” says Insem.
“Immediately after infection, the level of anti-Covid-19 antibodies is on average lower in women. But over time, it follows a decline which is generally less pronounced in them than in men, regardless of their condition. age or weight, ”the organization continues. In question ? A both hormonal and genetic explanation. Note: these results, established 6 months after infection, must be confirmed by longer-term follow-up.