Booster doses of monovalent and bivalent mRNA Covid-19 vaccines provided similar and strong initial protection, showed a study conducted in Canada.
Published on MedRxiv, a portal for preprints or preliminary reports that have not yet been peer-reviewed, the study estimated the effectiveness of booster doses of monovalent and bivalent mRNA Covid-19 vaccines against Omicron-associated severe outcomes among adults aged below 50 in Canada’s Ontario.
The study counters the latest reports published in the New England Journal of Medicine (NEJM), which show that bivalent Covid-19 vaccines provide significantly better protection – an edge in the efficacy of around 37 percentage points – than their monovalent counterparts against severe disease and death from infections caused by Omicron subvariants.
“Monovalent and bivalent mRNA Covid-19 vaccines provide comparable levels of initial protection against Omicron-related severe outcomes among community-dwelling adults aged ≥50 years in Ontario,” stated the study, which was uploaded on April 11.
Vaccine effectiveness of monovalent and bivalent vaccines ranged from 85 to 88 percent and 83 to 86 percent. The effectiveness was noted seven to 29 days after vaccination.
“There was only a slight waning of protection against severe outcomes across the four-month period,” stated the study.
After 90 to 119 days, effectiveness of monovalent vaccines decreased to 82 per cent whereas effectiveness of Moderna BA.1 bivalent vaccine decreased to 76 percent. The study also noted that the effectiveness appeared “slightly lower” in the BQ variant’s predominant period compared to the BA.4/BA.5 period, where comparisons were possible adding that “though uncertainty remains whether a true difference exists”.
According to Dr Rajeev Jayadevan, co-chairman of the Indian Medical Association’s national task force on coronavirus, it is “immune imprinting” that is responsible for the lack of difference between monovalent and bivalent vaccines.
“By 2023, most people have had immune exposure to this virus, either by infection, vaccination or both. Hence, vaccines delivered in such a setting will generate a similar response because of immune imprinting,” Dr Jayadevan said.
The study – supported by funding from the Canadian Immunization Research Network, Public Health Ontario and Ontario Ministry of Health – included 16,247 unique individuals and more than 14,999 test-negative controls. Approximately 57 percent of the cases and 69 percent of controls had their fourth dose as their most recent.
Need for second generations vaccines in India
The current vaccines used in India are monovalent. It means that these vaccines are designed to target one specific variant of a virus – the original coronavirus. Whereas a bivalent vaccine targets the specific spike mutations seen in the strain, which has mutated several times to create subvariants and is termed a “second generation” vaccine.
In a recent interview with News18, former director of All India Institute of Medical Sciences, Dr Randeep Guleria said similar to flu shots, India might need to update its Covid boosters with the latest strain of the coronavirus.
A renowned pulmonologist, Dr Guleria said the vaccines in India were currently using the Wuhan strain or the strain that was circulating in December 2019.
“By now, the strain of the virus has changed and evolved dramatically. From alpha, beta, delta to now omicron and its sub-lineages, the virus has mutated long back,” he said.
Dr Guleria further said when Indian vaccines were tested in trials, they reported an efficacy of 80 to 90 percent. “But now, the effectiveness of these vaccines against the latest strain might have come down significantly,” he said.
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