Covid-19 vaccines using mRNA technology were found to be the best in preventing symptomatic infection against variant strains, a comparison of the efficacy levels of different vaccines against the variants showed.
mRNA vaccines, especially those developed by Pfizer-BioNTech and Moderna, involve injecting clips of the genetic material of the virus – not the entire virus – into the body to elicit an immune response.
Vaccine mRNAs were found to induce high levels of neutralizing antibodies against the parent strain, as well as against British strain B117 and the Brazilian variant P1.
However, these levels of neutralizing antibodies decline when used against the South African version of B1351.
Neutralizing antibodies bind to specific, important sites of the virus, preventing it from initiating invasion.
The success of the mRNA vaccine is likely due to the high levels of antibody and T-cell responses they induce in the body, according to Associate Professor David Allen of Yong Loo Lin School of Medicine at National University.
“Antibodies have the ability to completely block the infection … and when it comes to limiting the spread and severity of the infection in an already infected person, T cells and antibodies play a role,” said Prof. Allen.
More traditional, inactivated vaccines use killed virus particles. They may cause lower reactions or none at all.
People with low levels of neutralizing antibodies can still be protected from Covid-19 if they have robust T-cell immunity. The immune system depends on T cells, a type of white blood cell, which together with antibodies eradicate the virus.
These findings were shared in a monthly webinar titled “Second Season of Covid-19: Updates from Singapore” on Thursday. The webinar brought together domestic and international experts to discuss the latest medical and scientific findings around the coronavirus.
The show was hosted by prof. Allen; Professor Dale Fisher, Director of Medicine at the National University Health System and Chair of the World Health Organization’s Global Warning and Response Network; and Dr. Louisa Sun, assistant advisor to the infectious diseases team at National University Hospital and Alexandra Hospital.
Work on variant-specific vaccines has already begun globally, said Dr. Richard Hatchett, a special guest on the show. Dr. Hatchett is the CEO of the Coalition for Epidemiological Preparedness, an international coalition formed to prepare for future threats of infectious diseases.