How Long Will Your Coronavirus Vaccination Last?

Share

YALE MEDICINE

BY KATHY KATELLA

[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.)

Akiko Iwasaki, PhD

“Data on the gradual decline of the antibodies in recipients of the mRNA vaccines suggest that they are likely to induce strong protection for a long time,” says Akiko Iwasaki, PhD, a professor of immunobiology at Yale School of Medicine. Photo by Robert A. Lisak

Another measure is T cells, which scientists are still studying for their ability to kill virus-infected cells in the context of COVID-19, and which may also provide important protection. T cells are more difficult to measure, Iwasaki says. But they may be important—last year, a study in Nature showed that people who were infected with severe acute respiratory syndrome (SARS), a different coronavirus outbreak that killed almost 800 people in 2003, maintained T-cell immunity 17 years after they recovered.

Still another way to predict how long protection might last is by looking at natural immunity, says Dr. Meyer. This means studying immunity people developed after infection with COVID-19. “We know for at least the first few months after symptomatic disease—and even longer—that people are unlikely to become reinfected,” she says.

But it’s important to know that immunity induced by the mRNA vaccines is stronger and more reliable than natural immunity, says Iwasaki. That’s because levels of natural immunity tend to differ from person to person. “Vaccines normalize the response to a very high level, where it uniformly uplifts everybody,” she says. “If you are starting with the high level, even if you start to decline from that level, it will take much longer before you need a booster.”

This is a reason why the Centers for Disease Control and Prevention (CDC) recommends vaccinations for people who have had a COVID-19 infection as well as for those who have not.

Could one type of vaccine last longer than another?

No one knows for sure whether one vaccine will last longer than another. Instead, one question to ask might be whether Pfizer and Moderna’s mRNA vaccines, which had an especially robust response, also have potential to be the longest lasting, Dr. Meyer says.

The two mRNA vaccines use a relatively new technology that delivers a tiny piece of genetic code from the SARS CoV-2 virus into the body to provide instructions for making copies of spike proteins that will stimulate an immune response. The Johnson & Johnson vaccine takes a more traditional approach that involves an inactive adenovirus (a common virus that can cause colds and other illnesses when it’s active).

“The mRNA vaccines are a novel tool that hasn’t been widely rolled out with any other virus, and so far in clinical trials they have had a much more robust immune response,” Dr. Meyer says. Whatever the answer to the question of which will last the longest, the Pfizer and Moderna mRNA vaccines work similarly, so it seems likely that they will have a similar impact on immunity, she says.

“It’s also possible that the length of immunity is somewhat dependent on the patient,” Dr. Meyer adds. While more research is needed, there could be variations in immune responses from person to person based on such factors as age, medical conditions, and medications they may be taking. Overall, though, the mRNA vaccines appear to be so effective that they level the playing field in terms of achieving protection from infection, says Dr. Meyer.

Will you need a booster shot?

To some degree, we will have to watch and wait while researchers monitor the continued efficacy of the vaccines over the coming months and years. If there is a change in the population’s immunity, people can expect the CDC to make new recommendations.

Jaimie Meyer, MD, MS

“I tell my family, ‘It’s great that you’re vaccinated… But even the vaccines don’t have 100% guarantees, so… you want to keep weighing the risks,'” says Yale Medicine infectious diseases expert Jaimie Meyer, MD, MS. Photo by Anthony DeCarlo

Meanwhile, if a new virus variant continues to circulate or becomes predominant—as is currently the case with the Delta variant—a component of the vaccines might need to be changed to reflect that variant, and vaccinated people might be given booster shots, Dr. Meyer says. “The good news is that Pfizer and Moderna made their mRNA vaccines easy to update,” she adds. “It just has to be tweaked a little bit, like having a computer code that needs a couple of minor edits. It’s relatively easy to build.”

What can we do in the meantime?

It’s critical that as many people as possible get vaccinated, Dr. Meyer says. “The hope is that the case rate will go down and more people will be less likely to be exposed.” That advice is especially important with the Delta virus, which has proven to be more contagious than previous variants, prompting the CDC to issue stricter guidelines calling for everyone—vaccinated or not—to wear masks indoors in areas of high transmission.

Even if Delta goes away, “I think those preventive measures will become even more important as the year passes, because potentially your immunity is going to wane over time,” Dr. Meyer says. Meanwhile, people need consider the amount of virus activity in their area, and what they need to do to protect the immunocompromised, and children and others who can’t get the vaccine. “I tell my family, ‘It’s great that you’re vaccinated. That’s wonderful, and you will have a lot more freedom and flexibility. But even the vaccines don’t have 100% guarantees, so whatever you do, you want to keep weighing the risks.'” she says.