Even though the antibodies against the coronavirus fade over time, the immune system has a backup plan that doesn’t rely on boosters, as per a study by scientists at the University of Pennsylvania, where technology for mRNA vaccines was developed.
For the study, the researchers at the university’s Perelman School of Medicine observed 61 people for six months after immunization with mRNA vaccines.
During the research, the team noted a gradual decline in antibodies, but that the vaccines generated long-lasting immune memory to SARS-COV-2 in the form of B and T cells that increased over time to help ward off serious illness.
“That was maybe a little bit surprising,” said Mr. John Wherry, director of the Institute for immunology. The research was released ahead of peer-review and publication.
Concerns that COVID-19 vaccines are providing a weaker shield against the more transmissible delta strain in countries that began immunizations early have prompted health authorities to consider offering third doses to boost antibody levels.
Although the third dose promise to strengthen antibodies and make them better at shielding from SARS-COV-2 for longer, the body has its own natural support to defend against COVID-19 even when circulating antibody levels decline, Mr. Wherry said. “Should antibodies wane and you get a little bit of local infection, you have memory B cells there to sort of renew or respond very rapidly to make new neutralizing antibodies,” he said.
Antibodies on mucosal surfaces lining the nose and throat block the coronavirus at its portal of entry, preventing it from causing an infection. But, as protective antibodies there fade, an infection is more likely to take hold, at least until new antibodies are triggered in response.
Mr. Wherry’s group found that memory B cells generated by the mRNA vaccines made by Moderna and Pfizer and its partner BioNTech appeared better at blocking virus variants including alpha, beta and delta, than those produced in response to a mild case of COVID-19. Additionally, high levels of vaccine-induced T cells, a type of white blood cell capable of finding and killing virus-infected cells, were detected after six months.
“We’re seeing a drop in efficacy when you only measure whether people get infected, but steady immunity if you’re measuring severe-disease outcomes. That fits with the idea that circulating antibodies are going to protect you from infection, but memory B cells and memory T cells, while they may not eliminate the ability to have some virus in your nose, they’re actually going to prevent severe disease,” Mr. Wherry said.
The findings help to explain why immunization remains effective at protecting against severe COVID-19, hospitalization and death even as more break-through infections occur.