the following article identifies how, although antibodies may diminish in months, they are not the 'whole story'; how the 'memory response is more important and how some vaccines may better be able to give a long immune memory
IMMUNE MEMORY IS MORE IMPORTANT
"Antibody responses are usually short-lived because once they have done their job you don't need them," said Jonathan Stoye, head of virology at Britain's Francis Crick Institute.
"But that doesn't mean that immunity, either induced by infection or by vaccination, is necessarily short-lived: Memory cells can respond to and combat a new infection."
Since SARS-CoV-2, the virus that causes COVID-19, is a new human virus, scientists don't yet know what levels of immunity will turn out to be protective. But many of the vaccine makers are touting both the antibody and T-cell responses, which are increasingly seen as important to lasting immunity.
"The immune system is very complicated. We know antibodies are important, but they're not the whole story," said Lawrence Young, a professor of molecular oncology at Britain's Warwick University. "The important thing here is immune memory."
Key to the process of immunity are memory cells known as T- and B-lymphocytes. Having made antibodies to a certain virus in an initial infection, the body uses these cells to remember that pathogen, "so when you are next exposed to the virus, the antibody response kicks in much sooner", Young said.
With vaccines, a key feature is that scientists developing them can select as targets the most important bits of the pathogen - in COVID-19's case these include the so-called "spike protein" on the surface of SARS-CoV-2 virus - to get the strongest and most lasting memory responses from T and B lymphocytes.
Some vaccines also contain stimulators or boosters, known as adjuvants, which can supercharge the response, and others are designed to be given in multiple doses to ensure higher concentrations of antibodies will create stronger memories.
"The idea is that while the natural infection may give you poor memory that may not last, the vaccine will give you strong memory that does last," said Danny Altmann, a professor of immunology at Imperial College London. https://www.medscape.com/viewarticle/939994