Health Matters: What do we know about how long immunity lasts after vaccination for COVID-19?
Dr. Chacko: Initially, we knew immunity lasted at least six months after vaccination, because the first trials had six months of data at that time. However, these studies are ongoing, and we now know that immunity actually lasts longer than we anticipated. At this point, we don’t know for sure how long it will last, but we do know that it is even longer than six months, which is exciting.
How do researchers assess immunity?
The participants who are in these studies are monitored regularly after vaccination. They receive regular blood tests to have their antibody levels checked and are also checked for breakthrough infections — meaning people who are infected with COVID-19 even after vaccination. Using those two factors and others, researchers are able to obtain more information about the expected duration of immunity.
Some sources state that immunity may be higher in people who have had COVID-19 and later got vaccinated. Is this true?
There has been some suggestion of that. The idea is that people who have had COVID-19 build a natural antibody response and then subsequently, when they are vaccinated, that vaccination builds upon the initial immunity to create an even larger immune response.
That being said, the CDC recommends everyone — even people who were infected with COVID — get vaccinated, because we do not know how long one is immune after recovering from COVID.
Are there certain types of vaccines that provide longer-lasting immunity than others?
A recent Nature study demonstrated that after the mRNA vaccines, people had very long-lasting immunity. They found that even up to 15 weeks after the first vaccination, participants had really active germinal centers (where immune cells are developed and trained in the body). This suggests that immunity from mRNA vaccines may last much longer than we originally anticipated.
There has not been a comparable study for the Johnson & Johnson vaccine, so we cannot assert if the same effect would be present. It should be noted that there’s an important distinction between real-world efficacy as compared to laboratory analysis of things like antibody levels or immune cell responses. But the good news is that there are several studies going on right now which are looking at all of these different factors.
What are booster shots and how do they work?
For some vaccines, as time goes on, immunity decreases, and so a booster shot refreshes the immune response. An example of this is the tetanus shot, which you have to get every 10 years to ensure continued immunity.