Being immune to Covid over eight months after infection? This is the conclusion reached by a team of Australian scientists in a study released this Tuesday 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.
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.