Effectiveness of 2 of 3 COVID-19 Vaccines Used in US Drops Below 50 Percent After 6 Months: Study

An 11-year-old girl watches as a nurse prepares a syringe with a dose of Pfizer's COVID-19 vaccine, at The Children's Hospital at Montefiore in New York City on Nov. 3, 2021. Mary Altaffer/AP Photo

The effectiveness of the three COVID-19 vaccines available in the United States has declined in recent months, with protection against infection falling under 50 percent for two of them after six months, according to a new study.

Moderna’s COVID-19 vaccine dropped to 58 percent in September from 89.2 percent effectiveness in March, researchers found. During the same time frame, Pfizer’s COVID-19 vaccine fell to 43.3 percent from 86.9 percent, and Johnson & Johnson’s shot declined to 13.1 percent from 86.4 percent.