Great amount of research and clinical studies are being done to increase the efficacy of vaccines for seasonal influenza virus, an epidemic of global concern. Currently available candidates lack effectiveness against different strains of flu. As a result, the reformulation of vaccines is needed more frequently and is a global challenge. Against this backdrop, a team of researchers at Perelman School of Medicine at the University of Pennsylvania have come up with a vaccine candidate that claims to have broader protection—long-term protective immunity—against several common types of influenza virus strains. The vaccine candidates made from in modified vitro-transcribed messenger RNA (mRNA) are shown to induce long-term protective immunity against multiple virus strains in mice, rabbits, and ferrets.
Constant Mutation by Glycoprotein on Virus Surface evades Protection against Vaccines
The researchers showed that the vaccine candidate essentially targets a glycoprotein found on the surface of influenza viruses called hemagglutinin HA. A large number of HA immunogens have been formulated over recent years but these have been found to be ineffective against the escape mutations that the virus undergoes to protect against killing by host cells.
A key limitation of all candidate vaccines have been their inability to get over plasticity of the HA head that underlies the cause between antigenically distant influenza virus strains. In recent years, most vaccine candidates based on mRNA have been found to be incapable of combating viral antigenic drift.
Next Step to develop Universal Vaccine for Humans
The researchers claimed that for the first time they developed vaccines formulated with mRNA molecules for the lower stalk of HA, the part of the virus not easily affected by mutation. This vaccine when injected in animals generated copies of HA to induce responses in a conserved region, leading to a broad protection. In one of the experiments the effects of the vaccine response on the mice were studied was 30 weeks with vaccine given over an interval of over four weeks. The response was then measured for three different flu strains.
The researchers are next contemplating to test the effectiveness of the vaccine candidates against non-human primates as well as humans. The findings of the study are published in the open journal Nature Communications on August 22, 2018.