Effectiveness Declines for All 3 COVID-19 Vaccines Over Time in Large Veterans Study

Efficacy of COVID-19 vaccines from Pfizer, Moderna, and J&J fell between 35% and 85% among nearly 800 000 US veterans, found a consortium of investigators.

The effectiveness of the 3 Covid-19 vaccines approved by the US Food and Drug Administration dropped off significantly as the Delta variant became the dominant strain of the coronavirus circulating throughout the US, according to research just published in the journal Science.

Specially the study found that original efficacy provided by the vaccines from Pfizer/BioNTech, Moderna, and Johnson & Johnson fell between 35% and 85% among nearly 800 000 US veterans.

Study authors report that in March 2021 as the Delta variant began to emerge in at first isolated areas of the US, the 3 vaccines provided roughly equivalent protection. By September, however, efficacy of the 2-dose series from Moderna had fallen to 58% from the original reported 89%; the Pfizer BioNTech 2-shot regimen saw a similar decline, from 87% to 45% efficacy over the 6-month period.

The largest drop in efficacy was observed for the Johnson & Johnson 1-dose vaccine—from 86% effectiveness to 13% between March and September.

The waning protection against infection remained even after adjustment for age, sex, and comorbidity, according to the investigators, led by Barbara A. Cohn, PhD, MHP, director of Child Health and Development at the Public Health Institute in Oakland, CA.

The study was conducted by researchers from Public Health Institute in Oakland, CA, the Veterans Affairs Medical Center in San Francisco, and the University of Texas Health Science Center and tracked 780 225 US veterans From February 1 to October 1, 2021. Approximately 500 000 were vaccinated and 300 000 were not. Researchers noted that the study population had 6 times as many men as women. About 48% of the study group was age ≥65 years, 29% aged 50-64 years, and 24% age <50 years.

In the oldest age group, ≥65 years, which was also the largest, Cohn et al found all 3 vaccines after just 3 months lost effectiveness to protect against death. For any vaccine at the time corresponding with the increase in prevalence of Delta infections, effectiveness against death was 71.6%; 52.2% for the J&J vaccine, 75.5% for Moderna; and 70.1% for Pfizer.

They write that risk of death was highest in veterans who were not vaccinated, regardless of age and comorbidity but stress that “breakthrough infections were not benign” and that protection against fatal breakthrough disease also varied by vaccine received.

Veterans aged ≥65 years who received the Moderna vaccine and had a breakthrough infection with SARS-CoV-2 were 76% less likely vs unvaccinated veterans to die of COVID-19 by July.

Those aged ≥65 who had received the Pfizer/BioNTech series and became infected were 70% less likely to die vs their unvaccinated peers. J&J vaccine recipients were least protected against breakthrough infection but were still 52% less likely to be fatally infected than unvaccinated veterans.

Among younger veterans, aged <65 years, vaccine effectiveness against a fatal case of COVID was 81.7% for any vaccine, 84% for Pfizer/BioNTech recipients, 82% for Moderna recipients, and 73% for J&J recipients, compared to unvaccinated veterans in that age group.

Their findings, Cohn and colleagues say, raise a number of concerns. Despite the apparent loss of efficacy of the 3 vaccines against infection, they did retain protection against death vs absence of vaccination during the surge of the Delta variant. “These results demonstrate an urgent need to reinstate multiple layers of protection,” they say, “such as masking and physical distancing – even among vaccinated persons – while also bolstering current efforts to increase vaccination.”


Reference: Cohn B, Cirillo PM, Murphy CC, et al. SARS-CoV-2 vaccine protection and deaths among US veterans during 2021. Science. 2021;10.1126/science.abm0620