Moderna COVID-19 Vaccine More Effective Than Pfizer Against Delta Variant: Study

A new preprint study published Sunday found that the COVID-19 vaccine developed by Moderna could be more effective in preventing an infection caused by the more contagious Delta variant than that developed by Pfizer-BioNTech.

In the study, which was published on preprint server medRxiv, a group of researchers from the Massachusetts data analytics company nference found that the efficacy of the Pfizer vaccine fell from 76% to 42% in July after the Delta variant became the dominant strain in the United States.

In comparison, Moderna’s shot fell from an efficacy rate of 86% to 76% in the same time period.

Additionally, Moderna’s COVID-19 vaccine was found to be 92% effective in preventing hospitalization, while Pfizer’s shot was 85% effective.

It is unclear whether the study’s results indicate that the vaccine shots become less effective over time or are less effective against the Delta variant. However, according to Venky Soundararajan, the lead author of the study, it could be a combination of both factors.

"The Moderna vaccine is likely — very likely — more effective than the Pfizer vaccine in areas where Delta is the dominant strain, and the Pfizer vaccine appears to have a lower durability of effectiveness,” Soundararajan said, according to Axios.

The authors of the observational study continue to emphasize that both mRNA vaccines are still highly effective in preventing coronavirus-related hospitalizations.

It should be noted that there are differences between both shots. Moderna has a stronger dose than the Pfizer shot, thus carrying a greater amount of mRNA. This may also account for the difference in the two vaccines’ effectiveness against the Delta variant, Soundararajan said.

"Thinking back, we think that might be because of the dose," he said, according to SF Gate. "There is more mRNA, which means it boosts a stronger immune response."

The researchers noted that a Moderna booster shot may be needed for anyone who received an mRNA shot earlier this year, as reported by Reuters.

The preprint study’s results are similar to that of a separate study that found that elderly nursing home residents and workers in Ontario produced a stronger immune response against COVID-19 when given the Moderna vaccine than the Pfizer jab.

In the study, residents who received the Pfizer shot produced antibody levels that were 3.89-fold fewer than those who received the Moderna shot.