Booster shots with mRNA vaccines such as those made by Pfizer and BioNTech failed to block infection with the omicron coronavirus variant in the first study of its kind, South African researchers said.
Seven German visitors to Cape Town experienced so-called breakthrough Covid-19 infections between late November and early December despite being boosted, the researchers, whose investigation was authorized by the University of Cape Town and Stellenbosch University, said in findings published in The Lancet on 18 January.
The findings add to evidence of the ability of omicron to evade the antibodies generated by Covid-19 vaccines. Still, other protections such as T-cells appear to combat the strain and so far hospital and mortality data has been less severe than with the delta variant.
The rapid global spread of omicron, first identified in Botswana and South Africa in late November, has spurred countries such as the U.K., the U.S. and South Africa to step up or introduce booster programs. However, the latest research suggests the plan may only be having a limited impact.
The Germans, four of whom were participating in training at Cape Town hospitals and three of whom were on vacation, were between the ages of 25 and 39, according to the researchers. Five were women and two were men. None were obese.
Of the seven, five had received three doses of the Covid-19 vaccine made by Pfizer and BioNTech. One had received a dose of Moderna Inc.’s mRNA shot followed by Pfizer’s inoculation. Another received the AstraZeneca Plc vaccine before shots of Pfizer. None reported a prior Covid-19 infection.
MRNA vaccines are the breakthrough technology of the Covid-19 pandemic. The shots use messenger RNA to instruct cells to produce antibodies. More traditional inoculations use inactivated or dead viruses to stimulate a response from immune systems.
“The presence of this group from Germany presented a unique opportunity to study omicron breakthrough infections in individuals with mRNA vaccine boosters,” the researchers said.
All of the subjects reported an onset of respiratory symptoms between Nov. 30 and Dec. 2, and ultimately experienced mild or moderate disease, they said.
“Robust CD4 and CD8 T-cell responses” were detected in the subjects, the researchers said in reference to an additional line of the human immune system’s defenses aside from the production of antibodies. “The mild to moderate course of illness suggests that full vaccination followed by a booster dose still provides good protection against severe disease caused by omicron,” they said.
Better vaccines will ultimately be needed to stop symptomatic infections with omicron, they said.