Immunity generated by the Moderna COVID-19 vaccine lasts for at least six months, and there is no indicator that vaccinated people will need a booster shot, according to a study. The research, published in the journal Science, noted that this time point of six months is critical because that is when true immune memory has formed.
While the Moderna COVID-19 vaccine led to strong immune 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 said. They 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. That's a good indicator of the durability of mRNA vaccines," said Shane Crotty, a professor at La Jolla Institute for Immunology (LJI) in the US. The researchers compared recovered COVID-19 patients to vaccine trial participants who received a 25-microgramme dose of the Moderna vaccine during the phase 1 clinical trials.
"We wanted to see if a quarter of the dose is able to induce any immune response," said study first author Jose Mateus Trivino, a postdoctoral fellow at LJI. "We had the opportunity to receive the samples from the original Moderna phase 1 trial participants who had received two 25-microgram injections of the vaccine, 28 days apart," Trivino said.
This vaccine dose is a quarter of the 100-microgram Moderna dose given emergency authorisation by the US Food and Drug Administration (FDA). While researchers don't know whether this smaller dose is as effective as the standard dose, the study shows that the T cell and antibody response in the smaller dose group is still strong.
They found that the Moderna vaccine spurs an adaptive immune response to the SARS-CoV-2 spike protein nearly identical to the immune system's response to a natural infection. The coronavirus uses the spike protein to enter and infect the cells.
"The response is comparable. It's not higher and it's not lower," said LJI Research Assistant Professor Daniela Weiskopf. The study also shows the power of "cross-reactive" T cells, immune cells which trigger a faster and better antibody response.
The researchers found that people with cross-reactive T cells had significantly stronger antibody responses to both doses of the vaccine. "If you have this immune reactivity, your immune system may kick in faster against the virus. And multiple studies have shown that how quickly the immune system reacts is key, the researchers added.
