[Originally published: May 20, 2021. Updated: August 6, 2021.]
If you are fully vaccinated, you may be excited about gathering with family and friends again. You might even be planning a winter vacation. But there are still nagging questions about how long protection from the coronavirus vaccines will last. For instance, will your shot wear off gradually or suddenly? Will you need a booster? Unfortunately, we can’t answer these questions with certainty yet. While the vaccines have provided strong protection against COVID-19 up to now, scientists need to monitor them over a longer period to fully understand their capabilities.
“We can only say that a vaccine is protective as long as we are measuring it,” says Yale Medicine infectious diseases specialist Jaimie Meyer, MD, MS.
In the meantime, there are a few things we know. One is that the Pfizer-BioNTech and Moderna mRNA vaccines have performed well so far. The most recent Pfizer-BioNTech data shows 91% overall efficacy falling to 84% at the six-month mark, and a steady 97% against severe disease, based on a July preprint that has not been reviewed by outside scientists. Moderna’s vaccine was 93% effective overall through six months and 98% effective against severe disease, according to a company statement in August. The latest data does not specify effectiveness against Delta.
Other research shows both mRNA vaccines set off an immune response that could last much longer—even years—against the original virus strain, based on a study published in July in Nature. That study did not include the Johnson & Johnson vaccine, which was authorized a couple months later than the other two, and which scientists are still gathering data on.
“The current data on the [Pfizer and Moderna] mRNA vaccines is very promising,” says Akiko Iwasaki, PhD, a professor of immunobiology at Yale School of Medicine and an investigator of the Howard Hughes Medical Institute.
How are we monitoring the coronavirus vaccines?
Pfizer and Moderna continue to monitor immunity in people who were given their vaccines in the initial clinical trials. One thing researchers are monitoring in vaccine recipients is levels of antibodies, which are proteins produced by the body’s immune system when it detects harmful substances, and that are easily measured from blood samples. “Antibodies are a really good marker for protection against infection, so we will be monitoring those levels for as long as we can measure them,” Iwasaki says.
A report in The New England Journal of Medicine (NEJM) in April showed that 33 participants who had received the Moderna vaccine during the Phase I trial had a gradual decline in antibody protection—and, based on the slope, Iwasaki says that is hopeful news. “If antibodies are going down very quickly, you would expect that to last for a short time.” The slow decline raises hopes that the mRNA vaccines will be protective for at least a year, if not longer, she says. (It should be noted that the trial occurred prior to Delta becoming the predominant virus variant.)