A new study has shown that as the Delta variant of the coronavirus has become the dominant strain in the United States, all three available vaccines for COVID-19 have lost some of their protective effects, with effectiveness ranging between 35% and 85% among a large group of veterans. Researchers who examined records of about 800,000 American veterans found that in early March, when the Delta variant began entering American communities, the three vaccines were nearly equal in their ability to prevent infection.
However, this changed significantly during the following six months. By the end of September, the effectiveness of the two-dose Moderna vaccine had dropped to just 58%, down from 89% in March. The effectiveness of the two-dose Pfizer-BioNTech vaccine decreased from 87% to 45% over the same period. More notably, the protective power of the single-dose Johnson & Johnson vaccine plummeted from 86% to 13% during those six months.
The study, whose results were published in the journal Science, was conducted by a team from the Public Health Institute in Oakland, the Veterans Affairs Medical Center in San Francisco, and the University of Texas Health Science Center.
