(CTN News) – COVID-19 mRNA vaccines are currently being used in the U.S. to prevent hospitalization and death. In the U.S. alone, the vaccines have prevented over 2 million deaths and over 17 million hospitalizations, according to the Commonwealth Fund.
The vaccines have not provided long-term immunity to prevent breakthrough infections – cases of COVID-19 infection in people who are fully vaccinated.
Activating longer-term immunity
We’re not sure why mRNA vaccines work so well at preventing COVID-19, but not so well at protecting against breakthrough infections. For stopping new infections and controlling the pandemic, it is crucial to understand this concept.
Compared to other infections, COVID-19 is unusual in that most people who get it recover with mild to moderate symptoms, while a small percentage get the severe form that can lead to hospitalization and death.
As part of the process of developing more targeted vaccines, it is important to understand how our immune system responds to mild versus severe forms of COVID-19.
Why booster shots?
After mounting an initial immune response, B cells and T cells become memory cells. Memory cells can remain in the body for several decades and mount a rapid response when they encounter the same infectious agent. Some vaccines against diseases such as smallpox provide protection for decades due to such memory cells.
However, for certain vaccines, such as hepatitis, multiple doses of a vaccine are necessary to boost immunity. As a result, the first or second dose is not sufficient to elicit robust antibodies or to sustain memory B- and T-cell responses.
Increasing the number of B cells and T cells that can respond to the infectious agent is achieved by increasing the immune response. In addition to boosting immunity, it also triggers the memory response.
COVID vaccine boosters
In spite of the fact that the third dose – or first booster – of COVID-19 vaccines was highly effective in preventing the severe form of COVID-19, protection against infection lasted less than four to six months.
The diminished protection even after the third dose is what led the CDC to recommend the fourth shot of the COVID-19 vaccine – or second booster – for people who are immunocompromised or who are over 50 years old.