Researchers from the United States compared the effectiveness of two mRNA vaccines – from Pfizer and Moderna, respectively-against the delta strain of coronavirus. With a general decrease in effectiveness for drugs, the risk of infection for those who received the Moderna vaccination was almost half less. The results of the study are presented in a preprint on the medRxiv website.
The “Delta” strain of coronavirus was first described in India in December 2020 and has recently become prevalent in most countries worldwide. It is more contagious, and COVID-19 is more severe with it.
The researchers observed more than 50 thousand people who were vaccinated from January to July 2021 to track the dynamics of the effectiveness of vaccines over time. Scientists tracked both cases of infection of vaccinated people and cases of their hospitalization. For the latter, the effectiveness of both drugs in July, when the “delta” strain began to dominate in prevalence, remained high-81 percent for Moderna and 75 percent for Pfizer.
“However, the effectiveness against infection has decreased for both vaccines,” the experts note in their work. While for the drug Moderna, this figure was 76 percent, it was 42 percent for Pfizer. The risk of infection for those vaccinated with the Pfizer vaccine was almost twice as high as those who received Moderna, the researchers note.
