A head-to-head comparison of the two mRNA-based COVID-19 vaccines has found one is performing better in the real world than the other.
While both are very effective at preventing serious illness and death, Moderna's SpikeVax - also known as mRNA-1273 - appears to be slightly more effective at preventing infection than Pfizer-BioNTech's Comirnaty, also known as BNT162b2.
In their phase III trials involving tens of thousands of volunteers, both vaccines recorded efficacy against infection in the mid-90s - 95 percent for Pfizer-BioNTech, 94 percent for Moderna.
"However, head-to-head comparisons of these vaccines have been lacking, leaving open the question of which vaccine is more effective," scientists from Harvard University wrote in the New England Journal of Medicine this week.
While based on the same cutting-edge technology, the two vaccines differ slightly in how much mRNA they contain, the recommended gap between doses and the composition of the lipid nanoparticle which carries the mRNA.
"These differences might explain emerging evidence for a higher antibody response among recipients of the mRNA-1273 vaccine than among recipients of the BNT162b2 vaccine. It has been suggested that this observed difference in antibody levels translates into a difference in the risk of Covid-19 outcomes."
The scientists looked at 440,000 vaccine recipients - half of whom got Pfizer-BioNTech, the rest Moderna - and compared infection rates. They found those who got the Pfizer-BioNTech jab were 27 percent more likely to be infected and 70 percent more likely to be hospitalised - 5.75 per 1000 compared to 4.52 per 1000.
The discrepancy could be down to how quickly protection wanes - the study finding no difference in infection rates in the first week or two after the first dose, widening at the 24-week mark.
"The risks of outcomes were low, regardless of the vaccine received," the researchers said, noting that both vaccines are "strongly recommended" considering the threat COVID-19 poses.
New Zealand pencilled in a deal with start-up Moderna late last year before deciding to go with Pfizer-BioNTech for the main rollout in 2021. It's recently also started offering the AstraZeneca vaccine for those who can't or won't get an mRNA-based jab.
Moderna's SpikeVax is on the Government's list of approved vaccines for those who got their jabs overseas and need a My Vaccine Pass.
