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. Health officials have continued to monitor data, and with the rise of variants, such as the highly contagious Delta variant, they are keeping a close eye on breakthrough infections and waning immunity.
There is some encouraging news. In late August, the CDC got new data that the vaccines continued to provide strong protection against severe disease even after the Delta variant had become the dominant variant in the United States. The data showed that the Pfizer, Moderna, and J&J vaccines remained highly effective at preventing hospitalizations from April to July.
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.
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.