Does Covid immunity change depending on the seriousness of the disease? This is what seems to say the different studies conducted on the matter as for the effectiveness of antibodies and their time in one's body. According to searchers from La Sorbonne, the Hôpital de la Pitié-Salpêtrière, the INSERM and the Institut Pasteur, their could stay in some people's bodies up to two to three months maximum. Anyway, this is what their work reads, as it has been published this Monday February 8, 2021 in Nature Communications.
What does this study say exactly? That neutralizing antibodies progressively disappear from one's body, sometimes even quickly, two months after contamination for those who got mildly sick. To make it to such an outcome, searchers have investigated "persistence of neutralizing antibodies among SARS-CoV-2-infected healthcare workers".
The scientists explain that all professionals developed antibodies between 2 and 4 weeks after the onset of symptoms, along with a neutralizing response to SARS-CoV-2. They go on saying these antibodies, the systemic IgA antibodies "declines [...] from two months after disease onset". They conclude: "this neutralizing activity appears to be transient with a decline, [...] associated with a decrease in systemic IgA antibody levels from 2 months after disease onset".
What does it mean? It means the body quickly generates antibodies but they disappear just as quickly. Results go against the other two studies, like the one led by Australian searchers and released on December 22, 2020 in Science Immunology, after assessing blood samples collected in 25 patients all infected with coronavirus. Samples that have been compared to a test group, in good health, and then they injected the virus to see how blood reacts.
A study showing that eight months following contamination, "SARS-CoV-2 infection generates long-lasting B cell memory [...] that could be protective against systemic disease upon reinfection". Scientists also managed to show that these T-cell lymphocytes rapidly generate "B-cell memory to both the spike and nucleocapsid antigens".
Yet, shall we be vaccinated immediately after being infected with Covid? A question answered by head of immunology unit at Paris Hôpital de la Pitié-Salpêtrière Guy Gorochov to La Dépêche: "For people the least at risk, and not given priority, we can consider a six months to a year-delay after being contaminated by Covid-19" he explains, unlike what the Haute Autorité de Santé recommends, naming a three-month delay.
Anyway, this release echoes the study led by scientists from La Jolla Institute of Immunology in a preprint study published on November 16, 2020. A study that assessed blood samples of 185 people that have been infected by Covid, with mild symptoms, and that led to rather encouraging results, since, six months past the infection, everyone that took part in the study were still showing a strong immune response.
And what is this study about? Searchers from the Institute have analyzed in the patients’ blood three kinds of immune response: antibodies, lymphocytes T – directly destroying contaminated cells – and lymphocytes B – secreting antibodies. According to Francetvinfo, “even in the event of a reinfection, such an immune memory would enable not to develop severe form of the disease for years”.
“We feared for people that caught mild forms of this coronavirus the immune response be relatively short. But careful, we’ve had feedbacks on the disease” professor Arnaud Fontanet commented on Wednesday November 18 on France 2. Good news then, and a study completing the previous ones on the matter, reinforcing the idea of a long-term immunity.
Immunity gets clearer over the months
Speaking of the first two studies, one American, the other Canadian, both released in Science Immunology on October 8, 2020, they caught scientists’ attention from all over the world. Two studies that assessed the length of immunity against Covid-19 after being infected and developing neutralizing antibodies.
Therefore, according to results released, these neutralizing antibodies could last at least three months after the first symptoms in patients infected with Covid-19. As for the Canadian study, scientists examined “the anti-SARS-CoV-2 antibody response over a 115-day period in the serum and saliva from 439 (serum) and 128 (saliva) patients with COVID-19”. Results compared with others, collected from 339 controls.
What did they discover? That IgG antibodies (immunoglobulin G), specific to Covid-19 have been found between 16 and 30 days after the first symptoms, and decreased only 105 days after (that is to say a bit over three months). Other antibodies, IgA and IgM, yet quickly disappeared from serum (the blood freed from its cells and coagulation proteins) and saliva. “Neutralizing antibodies reached their maximum by 31–45 days PSO – Post-symptom onset – and slowly declined up to 105 days, with a more pronounced drop in the last blood draw (105–115 days PSO)”, over a period of three months.
As for the American study, same stock: 95% of patients who took part in the study developed anti-RDB IgG antibodies 14 days PSO with a peak of IgM antibodies to 38% before IgG antibodies. The IgG antibodies level slowly decayed over a 90-day period before disappearing. Beyond this period, only 3 patients still had IgG antibodies detectable. A study that included 343 patients and took place for 122 days.
For the record, a study has been already carried out back in August when possible immunity was noticed after neutralizing antibodies were found in several sailors on a ship.
More encouraging results
Several months following these studies, and one year after the pandemic broke out, searchers from Strasbourg University Hospitals carried out a new study on how long antibodies are persistant following Covid-19 infection.
With more background than their peers, Strasbourg scientists managed to study 1,309 members of the hospital staff for one year, and 393 of them caught light SARS-CoV-2 and 916 of them have not been infected.
Their assessments bring more optimistic conclusions than the aforementionned studies: they say protective antibodies are still in patients over twelve months after infection. Even better: vaccines enable to improve their effectiveness.
"Searchers showed that in positive COVID-19, antibodies against the virus spike protein decline quicker in men than in women but stay in everyone up to 13 months following infection", the hospital release reads.
With only one dose of vaccine, searchers have noticed a strong increase in the number of antibodies in people, whichever vaccine they have been given. Furthermore, Strasbourg University Hospital doctors have noticed that the reinfection risk drops by 96.7% thanks to antibodies.
"By significantly increase protective antibody titers, one-dose vaccination reinforces protection against variants" Strasbourg University Hospitals virology unit head Pr. Samira Fafi-Kremer claims.
This si very good news enabling to see things in a more optimistic light. This study might also enable to rework the vaccination plan and eventually set up a less frequent booster shot.