The Pfizer-BioNTech COVID-19 vaccine, known as Comirnaty, is an mRNA vaccine that delivers genetic instructions to cells to initiate an immune response against the SARS-CoV-2 virus. This article explores how long the vaccine’s components remain in the body and the enduring immunological protection it establishes.
What Happens to Vaccine Components
The Pfizer-BioNTech vaccine introduces messenger RNA (mRNA) into the muscle cells at the injection site. This mRNA is a fragile molecule, encased within lipid nanoparticles for stability and delivery. Once inside the cells, the mRNA quickly delivers its instructions.
The mRNA is rapidly degraded by the body’s natural processes, usually within a few days, breaking into harmless pieces. The lipid nanoparticles, which carry the mRNA, are also broken down and cleared quickly, often within days. These components do not persist in the body long-term.
How the Body Builds Protection
Following injection, the mRNA instructs muscle cells to produce a harmless piece of the SARS-CoV-2 spike protein. This process occurs at the injection site and in nearby lymph nodes. Spike protein production peaks around 24 hours after vaccination and lasts for a few weeks.
The body’s immune system recognizes these newly produced spike proteins as foreign. This recognition triggers an immune response, leading to the creation of antibodies and specialized immune cells known as memory B cells and memory T cells. These immune components help recognize and fight the actual virus if a person is exposed in the future.
Measuring Lasting Immunity
The protective effect of the Pfizer vaccine involves both antibodies and memory immune cells. Antibody levels, measurable in the blood, decrease over time after vaccination. Immunity against symptomatic COVID-19 can wane within six to nine months after the primary vaccination series.
Despite declining antibody levels, the immune system retains “memory” through long-lived memory B and T cells. These memory cells reside in various tissues, including the spleen, bone marrow, and lungs. Upon re-exposure to the virus, these cells quickly reactivate, mounting a rapid and effective immune response. This cellular memory provides sustained protection against severe disease, hospitalization, and death. Updated vaccines and booster doses reinforce these immune responses against evolving variants.
Clarifying Common Concerns
A frequent concern about mRNA vaccines is whether the mRNA can alter human DNA. The mRNA from the vaccine does not enter the cell’s nucleus, which is where DNA is stored. Therefore, the vaccine’s mRNA cannot integrate into or change human DNA.
Another misconception is “vaccine shedding,” the idea that vaccinated individuals can shed vaccine components. The Pfizer-BioNTech vaccine contains no live virus particles. Its components are not infectious and are not shed from a vaccinated person. The lasting protective effects are immunological.