All three COVID-19 vaccines still produce strong immune response eight months later, new study finds

(NEW YORK) — All three currently authorized COVID-19 vaccines still showed signs of a strong immune response eight months later without a booster, according to a study published Friday in the New England Journal of Medicine.

The study analyzed specific markers of immunity found in the blood of people vaccinated with Pfizer, Moderna and the Johnson & Johnson vaccines.

Echoing evidence from the real world, researchers found cellular signatures suggesting that all three vaccines produce strong and long-lasting protection from severe illness.

But the analysis also hinted at differences in the way the vaccines produce antibodies — with Pfizer and Moderna antibodies spiking and then fading quickly, while Johnson & Johnson antibodies started at a lower level but remained more stable over time.

“By month eight, antibody responses were comparable for these three vaccines,” said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, who coauthored the research.

Pfizer and Moderna vaccines rely on the same type of technology, called mRNA, while Johnson & Johnson uses a different technology, called viral vector. The two technologies prompt different types of immune responses.

Thought the pandemic, scientists have used antibodies — virus fighting proteins in the blood — as one indication that vaccines are working. But antibodies are only one part of the body’s overall immune response.

This new study is among the first to directly compare not just antibodies, but also T-cells, across all three vaccines. T-cells are also a crucial part of the immune system, and may offer longer-lasting protection even after antibodies fade.

“We think the antibodies are often more relevant preventing against infection, and the T-cells are more relevant killing the virus — so preventing severe disease,” said Dr. Todd Ellerin, director of infectious diseases at South Shore Health and an ABC News medical contributor.

“T-cell responses likely contribute to vaccine protection against severe disease,” said Barouch. “T-cell responses were relatively stable for all three vaccines for eight months.”

The study helps explain on a cellular level an observation that public health experts are seeing in the real world — protection against severe disease is holding strong, even as protection against mild breakthrough infections fluctuates over time.

“The higher the neutralizing antibody titers, the more protected you are against infection,” Ellerin said. “I think that’s why there’s an advantage to two doses of mRNA vacancies compared to the single dose Johnson & Johnson against preventing infection.”

But, Ellerin said, “When it comes to severe disease, that’s a completely different story. And they all do great.”

For scientists and doctors currently debating need for booster shots, the study underscores the fact that even 18 months into the pandemic, there’s no one test that can perfectly measure how protected a person is from COVID-19 — potentially muddying the waters about the best time to boost.