Half of People Who Got Pfizer Have Lower Antibodies—Here's Why

A new study has pinpointed a group that doesn't get as much protection from the COVID shot.

Over the past several months, health experts and officials have analyzed the protection granted by Pfizer's vaccine. Recent research has shown that while Moderna's vaccine remains rather stable over time, the other mRNA vaccine appears to wane in its protection against infection, despite using similar technology. Recently, the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) determined that the effectiveness of Pfizer's vaccine diminishes enough to warrant the authorization of booster shots for certain groups of people. Now, new research shows that a much larger group could have lower antibodies from the Pfizer shot.

RELATED: If You Got Pfizer, This Is When Your Protection Drops Below 50 Percent.

For a study published Oct. 6 in The New England Journal of Medicine, researchers looked at the antibody response of Pfizer's vaccine among different demographics. The study analyzed more than 4,800 health care workers in Israel over the course of six months from December to July, following their second dose of Pfizer.

According to the study, antibodies from the Pfizer vaccine decreased for everyone six months after the second dose. IgG antibodies decreased at a consistent rate, but neutralizing antibody levels decreased rapidly during the first three months before slowing to a gradual reduction level.

But the researchers also found that women had higher levels of protection and were protected significantly longer than men after receiving the Pfizer vaccine. Throughout the entire course of the study, men had significantly lower neutralizing antibodies than women did, with an overall decrease of 36 percent. "Neutralizing antibodies have been shown to correlate with protection," the researchers noted.

The separation between men and women was even more apparent with age. By the end of the study, men over the age of 65 had a 37 percent lower rate of IgG antibodies and a 46 percent lower rate of neutralizing antibodies than women of the same age. "We analyzed the association of age, sex, and coexisting conditions with immunogenicity, both at the peak and at six months after receipt of the second dose. We found that antibody levels in both periods were higher in women than in men and decreased with age, as has been previously shown for the first month after receipt of the second dose," the study confirmed.

RELATED: For more up-to-date information, sign up for our daily newsletter.

This is not the first research to suggest that women gain more protection from COVID vaccines. A Feb. 26 study from the CDC found that women reported more side effects following coronavirus vaccine shots than men. Lead author Julianne Gee, MPH, a CDC epidemiologist, told Verywell that this study—and studies conducted before the authorization of COVID vaccines—seem to suggest that women have higher antibody responses than males to certain vaccines, including the coronavirus and flu shots.

"Women generally develop stronger immune responses, including high antibody levels and greater T-cell activation, which can lead to more rapid control of infection, but may also lead to increased reactogenicity (side effects) after vaccines," Gee explained.

It's important to note that another Pfizer study published Oct. 4 in The Lancet confirmed that the vaccine's protection against severe COVID is still strong over time, regardless of gender. According to the study, which analyzed more than 3 million individuals, Pfizer's effectiveness against COVID-related hospitalization was 90 percent overall for those fully vaccinated.

"Protection against hospitalization remains high over time, even when Delta predominates," study author Sara Tartof, PhD, an epidemiologist at Kaiser Permanente Southern California, told The New York Times. Against infection, the study found a similar reduction to the Israel study, noting that Pfizer's vaccine effectiveness fell from 88 percent during the first month after vaccination to 47 percent after five months.

RELATED: If You're Over 60, This Is How Much a Pfizer Booster Protects You, Study Says.

Filed Under