June 28 - July 4
A new study on the vaccination of people who have already been infected
Neutralising antibodies are an essential component of the immune response against SARS-CoV-2. In individuals who have not yet been infected, the 2 mRNA vaccines (Pfizer-BioNTech and Moderna), built using the original Wuhan strain of the virus, trigger the production of neutralising antibodies and have shown more than 94% efficacy. But recently, numerous SARS-CoV-2 variants have emerged, notably the Alpha (a, UK), Beta (b, South African) and Gamma (g, Brazilian) variants, which demonstrate varying levels of resistance to antibody responses as compared to the original virus. American researchers (Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, USA) have confirmed (see letter…) that vaccination of infected individuals could increase the neutralising response against the Beta variant.
The researchers studied the serum (containing antibodies) of patients vaccinated with an mRNA vaccine, who had either been naturally infected by the original strain of the virus, or not infected. It appears that in patients who had been naturally infected by SARS-CoV-2, a single dose of an mRNA vaccine enables the production of a level of neutralising antibodies superior to levels observed in non-infected individuals having received two doses of the vaccine. However, mutations found in the Beta variant reduce sensitivity to neutralisation in the serum of recovered or vaccinated patients.
So, although we knew before that this neutralising antibody response appeared to be greater, is it really more effective against the Beta variant?
To reply to this question, the scientists carried out neutralisation tests on the original strain and on the Beta variant. A single dose of the vaccine enabled neutralisation against the variant to be strengthened in individuals having already been infected by the original strain, even though their level of neutralisation did not reach levels of efficacy observed against the original Wuhan strain.
Vaccination with a dose of mRNA vaccine in patients who have already been infected by the original virus strain does therefore lead to an increased neutralisation response, even against the Beta variant. Now we need to examine whether this antibody response persists over a longer period of time and discover whether a second dose for these patients will be necessary.