Six to 18 months after you receive your second dose of the Pfizer vaccine, you may still be at risk for developing COVID-19, but you are highly protected from getting serious disease that can result in hospitalization, intubation and death. The CDC recommends a third booster dose of the Pfizer vaccine for people over 65, those with immune-compromising health conditions and those in high-risk environments. Similar recommendations are expected soon for Moderna and J&J vaccine boosters. In my opinion, anyone who is concerned about his or her immune status should get a booster shot.
Six months after the second Pfizer COVID-19 vaccination, antibody levels and immunity drop significantly, even though the vaccinated person is still protected from serious disease. In a study from Quatar, six months after second vaccination 20 percent were protected from disease and almost 100 percent were protected from serious disease, hospitalization and death (NEJM, October 6, 2021). An Israeli study showed that protective blood antibody levels drop significantly six months after the second Pfizer immunization (also in NEJM, Oct 6, 2021).
When a virus or vaccine enters your bloodstream, your immunity produces antibodies that try to attack and kill the virus. However, antibodies have a limited lifespan and eventually disappear from your bloodstream. Both vaccinations and infections cause your body to produce memory B cells that can last for a lifetime, so the next time that virus tries to enter your cells, the memory B cells quickly respond by stimulating your immunity to produce large amounts of antibodies that try to kill that virus. Memory B cells for the Spanish flu are still present 100 years later and those for smallpox last more than 50 years.
Vaccinations produce greater amounts of circulating antibodies than natural infection, but the live virus that causes natural COVID-19 infections stays around in your bloodstream for a longer period of time than the vaccination and produces longer-lasting and more-potent memory B cells that can produce antibodies many years later. However, a natural infection can hospitalize and kill you, while vaccinations almost never do that (Nature, October 7, 2021) https://doi.org/10.1038/s41586-021-04060-7
Dr. Gabe Mirkin is a Villager. Learn more at www.drmirkin.com