You may be among the more than 106 million people in the United States who have taken at least one dose of a coronavirus vaccine. Or perhaps you may still be waiting for your turn. Nevertheless, there’s an important question on our minds: How long will the vaccine protect us?

The answer is not completely clear. Because although we have been battling the pandemic for more than a year, Due to the relatively recent vaccine emergency use authorization, experts have not had time to observe their long-term effectiveness.

Research is currently underway, and in the meantime, experts say we can make an educated guess.

Federal health authorities have not provided a definitive answer to this question of how long the COVID-19 vaccine lasts in the human body. However, based on clinical trials, experts do know that vaccine-induced protection should last a minimum of about three months. That does not mean protective immunity will expire after 90 days; that was simply the time frame participants were studied in the initial Pfizer, Moderna and Johnson & Johnson trials. As researchers continue to study the vaccines, that length of time is expected to grow. The protection should last longer, though the length of time still needs to be determined with further studies, experts said.

Ian Haydon helped test the Moderna coronavirus vaccine last year. Now, he’s helping test the tweaked version of that vaccine designed to fight the new, more contagious variant.

“A year ago I tried the Moderna vaccine to see if it was safe. Now, on my #COVIDvaccine anniversary, I’m happy to share that I just got a 3rd dose. This booster experiment will reveal (1) if strain-adapted vaccines boost immunity & (2) whether they are safe,” Haydon, a communications specialist at the University of Washington, said via Twitter last Saturday.

Doctors are worried that coronavirus may end up being like influenza, which requires a new vaccine every year both because the circulating strains mutate fast and because immunity from the vaccine wears off quickly.

Although initial evidence suggests immunity from vaccination against coronavirus provides long-lasting protection, vaccine makers have begun making and testing versions of their vaccines that protect against worrying variants of the virus. That includes the B.1.351 version first seen in South Africa, which carries a mutation that, in lab experiments, appears to allow it to evade the human immune response a little.

The latest report from vaccine maker Pfizer shows people in South Africa who got its coronavirus vaccine after B.1.351 became the dominant circulating virus were still very strongly protected from infection — something that backs up laboratory experiments that have shown the vaccine causes such a strong and broad immune response that it provides a cushion against any effects of mutant viruses.

“It is still matched enough that we have good protection,” said Scott Hensley, an immunologist and vaccine expert at the University of Pennsylvania.

But vaccine creators are not taking chances. The trial Haydon is taking part in is testing not only a third dose of Moderna vaccine altered to protect specifically against B.1.351 — that’s what he received — but a third dose of original vaccine in some volunteers, too, to see if the boosted immune response is both safe and provides an additional advantage.

A report released last month from Pfizer suggests people who get both doses keep strong immunity for at least six months. Experts point out that doesn’t mean immunity stops at six months. It means that’s the longest volunteers in the trials have been followed to see what their immunity is. It’s likely to last much longer, Hensley said.

“I would not be surprised if we learned a year from now that these vaccines are still producing a strong immune response,” Hensley told CNN.

“I would not be surprised if this is a vaccine that we only get once.”

That would make the vaccine more akin to vaccines against measles than flu vaccines. Vaccination against measles protects against infection for life in 96% of people.

Protection from Pfizer’s two-dose vaccine remains above 91% even at six months, according to the company. Details were recently released in a statement, not a formal scientific publication, and the data covers only a few thousand people. Experts say if it holds up, that’s an indication that both the Pfizer and Moderna vaccines elicit a long-lasting immune response.

Hensley says the technology used by both vaccines — delivery of genetic material known as messenger RNA of mRNA — is especially potent.

“The antibody responses elicited by these mRNA vaccines are incredibly high. What we know in animal models with other mRNA vaccines that have been tested previously — we know that those antibody responses are incredibly long-lived and they don’t drop over time,” said Hensley, whose lab has been testing experimental mRNA vaccines for years.

In January, a team led by Dr. Alicia Widge at the National Institute of Allergy and Infectious Diseases wrote the New England Journal of Medicine to say their research showed two doses of Moderna’s vaccine produced plenty of antibodies that declined only very slightly over time. The vaccine also caused the body to produce immune cells known as T cells and B cells that can keep defenses going for years. The vaccine-induced immune response was stronger and less variable than the immune response that follows a natural infection, they found.

“Although we do not yet know exactly what level of neutralization is required for protection against Covid-19 disease or infection, our experience with other vaccines tells us that it is likely that the Pfizer vaccine offers relatively good protection against this new variant,” Scott Weaver, director of the Institute for Human Infections and Immunity at University of Texas Medical Branch, told CNN at the time.

Nonetheless, last month, South African virologists argued that there is evidence the vaccines being developed do not work as well against B.1.351 and urged vaccine makers to start altering their formulas now.

Although he’s taking part in clinical trials that require regular blood draws to check his immunity, Haydon has no idea how well protected he is from the virus.

“I know that early on in the trial, myself and all the participants did develop neutralizing antibodies — the kind that you are looking for. That was clear many, many months ago,” Haydon said. “But the level of those antibodies, and how the levels have changed over time, is not something that I’m told. That is one of the main things that is being evaluated over the study.”

Haydon did have a strong reaction to the first round of vaccination and said the third dose he just recently received caused some effects, too.

“Flulike is the right way to describe my symptoms,” he said. “I ended up with a fever, chills, a little bit of nausea, headache”.

Immunologists say that’s a sign the immune system is responding to the vaccine, although people who report no symptoms also develop an immune response, so the symptoms do not appear to suggest someone’s having a better response than someone who doesn’t develop a fever.