A Centers for Disease Control and Prevention (CDC) study of hospitalized veterans showed their antibody response dropped four months after receiving either of the two mRNA COVID-19 vaccines.
Published Thursday, the CDC-backed study found that both the Pfizer and Moderna vaccines were effective at preventing hospitalization for veterans four months after they got their second dose, although their COVID-19 antibody levels dropped. Among those who received the Moderna vaccine, scientists recorded “slightly higher” COVID-19 antibody levels than those who received the Pfizer shot.
The researchers noted that four months after the Moderna and Pfizer vaccines were administered to the veterans, their effectiveness at preventing hospitalizations was 86 percent and 75 percent, respectively.
After their findings, the CDC again recommended that people receive a booster shot months after getting the vaccine.
“These findings from a cohort of older, hospitalized veterans with high prevalences of underlying conditions suggest the importance of booster doses to help maintain long-term protection against severe COVID-19,” the report said.
But the CDC noted that their study’s findings “are subject some limitations, including researchers’ inability “to assess antibody levels or [vaccine effectiveness] beyond 4 months since receipt of second vaccine dose.” They also noted that “there was insufficient statistical power to detect potential small differences in [vaccine effectiveness] by vaccine product or period since vaccination.”
The study evaluated about 1,900 veterans between Feb. 1 and Sept. 30 in five Veterans Affairs hospitals in New York City, Los Angeles, Atlanta, Houston, and Palo Alto, California.
Researchers measured the antibody levels among 234 veteran patients who obtained two vaccine doses and had no evidence of a prior COVID-19 infection, which results in what some scientists have termed natural immunity. Most of the patients were male with a median age of 67.
“Everyone ages 18 and older should get a booster shot either when they are six months after their initial Pfizer or Moderna series or two months after their initial J&J vaccine,” CDC Director Rochelle Walensky said earlier this month.