CDC Study: mRNA Vaccine Protection Against COVID-19 Is Waning

A health worker prepares a dose of the Moderna Covid-19 vaccine at a convention hall in Banda Aceh on Aug. 30, 2021. Chaideer Mahyuddin/AFP via Getty Images

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.

The study’s findings come as federal health officials have ramped up their push for more and more people to get booster shots. Meanwhile, some institutions—including colleges—have begun to mandate boosters for individuals to enter facilities.

On Thursday, the Food and Drug Administration (FDA) said it amended its emergency use authorization for Pfizer’s vaccine booster to allow youths aged 16 to 17 to get a third shot at least six months after their second dose. The CDC hours later signed off on the move.

Some scientists have raised concerns about the additional shot because of the elevated risk of rare cases of heart inflammation in young men that have been linked to messenger RNA vaccines such as the Pfizer/BioNTech shot.

All U.S. adults are currently eligible for booster shots of the three authorized COVID-19 vaccines.

Reuters contributed to this report.