How Long Does Immunity Last in COVID-19 Vaccinated People

California-based La Jolla Institute for Immunology (LJI) scientists’ new study helps answer the question: how long does immunity against COVID-19 last in vaccinated people?

As reported in the journal Science on September 14, 2021, a low dose of the Moderna, Inc. vaccine known as SpikeVax, immunity lasts for at least six months.

And no indicator vaccinated people will need a booster shot from this mRNA vaccine.

“This time point is critical because that is when true immune memory has formed,” stated LJI Research Assistant Professor Daniela Weiskopf, Ph.D., in a press release.

While the SpikeVax vaccine led to strong CD4+ (helper) T cell, CD8+ (killer) T cell, and antibody responses for at least six months after clinical trial participants were fully vaccinated, it is likely that the immune response could last much longer. 

The researchers also show that this strong immune memory lasted in all age groups tested, including in people over age 70, a demographic especially vulnerable to severe COVID-19.

“The immune memory was stable, and that was impressive,” added Dr. Crotty, who co-led the study. “That’s a good indicator of the durability of mRNA vaccines.”

The researchers compared recovered COVID-19 patients to vaccine trial participants who received a 25-microgram dose of the SpikeVax vaccine during the phase 1 clinical trials.

“We wanted to see if a quarter of the dose is able to induce an immune response,” says study first author Jose Mateus Triviño, Ph.D., a postdoctoral fellow at LJI.

“We had the opportunity to receive the samples from the original Moderna/ NIH phase 1 trial participants who had received two 25-microgram injections of the vaccine, 28 days apart.”

This vaccine dose is a quarter of the 100-microgram Moderna dose given emergency authorization by the U.S. Food and Drug Administration (FDA). 

While researchers don’t know whether this smaller dose is as effective as the standard dose, this new study shows that the T cell and antibody response in the smaller dose group is still strong.

In fact, the researchers found that the SpikeVax vaccine spurs an adaptive immune response to the SARS-CoV-2 spike protein (a key target) nearly identical to the immune system’s response to a natural SARS-CoV-2 infection. 

“The response is comparable,” says Weiskopf. “It’s not higher, and it’s not lower.”

The new study does not show that a lower dose of the Moderna SpikeVax vaccine provides the same protection as the standard dose. 

“It would take a clinical trial to tell you how protective the lower dose is,” says Crotty.

The new research also shows the power of “cross-reactive” T cells. 

In a 2020 Science study, the LJI team showed that T cells in people who had recovered from common cold coronaviruses could respond to the novel coronavirus, SARS-CoV-2. But, at the time, they didn’t know whether this cross-reactivity could protect against COVID-19. 

For the new study, the researchers found that people with cross-reactive T cells had significantly stronger CD4+ T cell and antibody responses to both vaccine doses.

The team also filled in a significant gap in COVID-19 vaccine research. 

Until now, many studies had shown an effective CD4+ T cell response to the SpikeVax vaccine, but CD8+ T cell data was lacking. 

“We know naturally infected, and recovered people develop excellent CD8+ T cell responses against SARS-CoV-2.”

“However, there was concern about the generation of CD8+ T cells by mRNA vaccines,” says Mateus Triviño. 

The new study shows a robust CD8+ T cell response to the low dose Moderna vaccine, similar to the response after a patient fights a natural SARS-CoV-2 infection, says Sette, a renowned T cell expert.

“We see a robust CD8+ T cell response—and we showed that using multiple assays,” adds Weiskopf.

This study, “Low dose mRNA-1273 COVID-19 vaccine generates durable T cell memory and antibodies enhanced by pre-existing cross-reactive T cell memory,” was supported by the National Institutes of Health’s National Institute for Allergy and Infectious Diseases, LJI Institutional Funds, and others.

Additional study authors include first author Jose Mateus, Jennifer M. Dan, Zeli Zhang, Carolyn Rydyznski Moderbacher, Marshall Lammers, and Benjamin Goodwin. No industry conflicts of interest were disclosed.

The La Jolla Institute for Immunology is dedicated to understanding the intricacies and power of the immune system so that we may apply that knowledge to promote human health and prevent a wide range of diseases. Since its founding in 1988 as an independent, nonprofit research organization, the Institute has made numerous advances leading toward its goal:  life without disease.

PrecisionVaccinations publishes fact-checked research-based vaccine news.