We Know Less About Immunizations Than We Thought

Some vaccines lose effectiveness more quickly--and others last much longer---than previously understood.

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A report in Science magazine is rather disturbing. Some vaccines we thought lasted a lifetime, don’t. Conversely, some booster shots are unnecessary. And flu shots? They diminish in effectiveness in mere weeks.

Like millions of people in the United States last year, Stanley Plotkin and his wife got vaccinated against influenza at the start of the Northern Hemisphere’s flu season, in early October. Plotkin, a physician and emeritus professor at the University of Pennsylvania, knew well the value of the shot: He is one of the world’s most renowned vaccinologists, having had a hand in several vaccines on the market, including the one for rubella. He’s even the co-author of the standard medical textbook, Vaccines.

In January, just 3 months later, the couple got a second flu shot.

That was an unusual choice, one not recommended by the U.S. Advisory Committee on Immunization Practices (ACIP), which guides the country’s vaccine usage. But a growing body of evidence that the protective immune responses triggered by flu vaccines wane in a matter of weeks persuaded Plotkin to return to the clinic. “The time and cost was trivial compared to the importance of influenza at my age,” says Plotkin, 86. “With flu, we’re not talking about getting a case of the sniffles.”

It’s not just flu. Recent studies show vaccines for mumps, pertussis, meningococcal disease, and yellow fever also lose their effectiveness faster than official immunization recommendations suggest. Vaccines have been a crucial public health tool for decades, so it may seem strange that their durability isn’t well understood. But vaccines are approved and come to market years before it’s clear how long protection lasts. Later, fading protection can go unnoticed because a vaccine in wide use has largely eliminated transmission of the microbes it protects against, making “breakthrough” infections rare. Even if viruses or bacteria are still in circulation, people vaccinated against them will sometimes receive natural boosting of their immunity. And declining vaccine immunity is not an all-or-nothing phenomenon: A breakthrough infection often leads to much less severe symptoms of the disease.

Researchers are ramping up efforts to figure out why some vaccines protect for mere weeks but others work for life. “We simply don’t know what the rules are to inducing long-lasting immunity,” says Plotkin, who began to research vaccines in 1957. “For years, we were making vaccines without a really deep knowledge of immunology. Everything, of course, depends on immunologic memory, and we have not systematically measured it.”

Bali Pulendran, an immunologist at Stanford University in Palo Alto, California, has reached the same frustrating conclusion about vaccine durability. “I keep saying, ‘It’s not well understood, it’s not well understood.’ This is one of the major issues in vaccines.” Deepening the confusion, two essential vaccines, against diphtheria and tetanus, appear to have better durability than widely presumed.


In a 2018 review of 11 recent studies on the durability of influenza vaccines, researchers concluded that effectiveness can vanish as soon as 90 days after vaccination. The article, published in Clinical Infectious Diseases, further noted that 20% of Americans received their flu vaccines for a given season by the end of September—which means the vaccine may do nothing come peak flu spread in January and February. “The further away you get from your vaccine, the higher the risk that you’ll contract influenza,” says study co-author Kunal Rambhia, a drug delivery specialist working on a Ph.D. at the University of Michigan in Ann Arbor. “This has huge implications.”

Rambhia says ACIP has good reason to urge people to get vaccinated early, given the challenge of immunizing more than 100 million Americans each year. “They’re making the best decision they can,” he says. “They acknowledge that the vaccine might be less effective toward the end of the flu season.”

He and others also note that a vaccine can offer a benefit even if it “fails.” In people who receive the flu vaccine but become ill, the disease often is markedly less severe. Such partial protection was first recognized more than a century ago with the smallpox vaccine, which fully prevents disease for only a few decades, but powerfully shields people from severe illness and death for life.

— Jon Cohen, “How long do vaccines last? The surprising answers may help protect people longer”

Elided in the excerpt is a longish discussion about how scientists are learning to make vaccines better. The first step is admitting that we know less than we thought—and they’ve taken that step.

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James Joyner
About James Joyner
James Joyner is Professor and Department Head of Security Studies at Marine Corps University's Command and Staff College. He's a former Army officer and Desert Storm veteran. Views expressed here are his own. Follow James on Twitter @DrJJoyner.


  1. Franklin says:

    Interesting, and I’d bet a dollar that the duration of the effectiveness is different for different people.

    This is the highly complex immune system we are talking about. The same system that sometimes reacts to benign proteins and causes an allergic reaction. Allergies change over time for unknown reasons. When my son was diagnosed with a peanut allergy at age two, we were told he only had a 20% chance of outgrowing it. Luckily, it appears that he probably will. Tests show that his immune system appears to be forgetting about peanut protein and produces relatively few antibodies in reaction to it now. But why him and not other kids?

    And then there’s the link to our microbiome. There are reports of allergies changing when people get fecal transplants. We do not know everything, that is for sure.

  2. John Peabody says:

    There are many people who will read this headline and assume that vaccines are fraudulent / ineffective. ‘Tis a shame.

  3. just nutha says:

    @Franklin: I outgrew my peanut allergy at least partially–less severe reactions to ingesting peanut–but it took over 60 years by my back of the envelope calculations. I hope your child does better.

  4. Kathy says:

    Combine the short windows of immunity with the number of different strains of flu, and it’s a wonder it works at all.

    In science often the answers to questions beget more questions. I sometimes wonder whether we will ever know everything there is to know about science. I think it’s possible, if humanity endures long enough. And yet, some questions may be impossible to answer.

  5. Slugger says:

    The immune system is an evolutionary response to a variety of invaders, but while we multicellular critters were evolving the immune system, the invasive bad guys were evolving ways of eluding it in an unending arms race. Immunization provides two benefits, personal and herd immunity. If everyone was immunized against this year’s flu, it might only last 90 days, but the effect on the herd would be to create a dam, a firebreak, a wall that would stop the transmission of that virus. Of course, next year there will be another strain.

  6. Stormy Dragon says:

    My primary care doctor has, for the last few years, been recommending holding off to late October for my flu vaccination for precisely this reason.

  7. Jen says:

    I was reviewing my shot record last week after reading a piece on CNN about how changes to the measles vaccine meant that a range of people around my age (Gen X) likely received less-effective dosages. On the back of the shot record it listed the frequency suggested for members of the military serving overseas (we were overseas for much of my childhood). I don’t have it in front of me right now, but I believe I counted 4 smallpox vaccinations, yellow fever and cholera were in the dozen or so range, polio I think was four (but that’s a series, right?) along with BCG (tuberculosis) and a bunch of others. This is a long way of saying well, the military at least used to require frequent rounds of these vaccinations, so clearly there must have been some suspicion that the effects wear off?

    Edit: Yellow fever was once every 10 years, the multiples are cholera DPT, Gamma globulin, typhoid, etc.

  8. Kathy says:

    BTW, and off topic, here’s an idea for a science fiction story:

    We meet very advanced, peaceful aliens whose technology meets Clarke’s Third Law: Any sufficiently advanced technology is indistinguishable from magic.

    All well and good, until they try to explain the science behind their technology, and realize there’s a quirk in the human mind that keeps them from understanding even some very elementary concepts and ideas.

    The problem with this idea is that it wouldn’t be possible for the reader to understand the science, either, or maybe even the human quirk, assuming the author could to begin with. It would be far easier, and far less interesting, to do it the other way around.

    But if anyone wants to run with it, just make sure to mention me in the acknowledgments.

  9. Just nutha ignint cracker says:

    @Stormy Dragon: The clinic that I go to was recommending postponing until December or January because flu traditionally peaks here in February, so even November can be too early.

  10. gVOR08 says:

    @Slugger: Evolutionary response? What are you, some sort of commnist?

    It gobsmacks me that people can deny evolution when we are literally permeated with it. I get that a lot of people don’t have the basic knowledge or inclination to evaluate scientific claims, but they’re being led to their denial by opinion leaders who are capable of knowing better, or at least have access to people who are. Denial by opinion leaders requires deliberate intent. Same with AGW. And they’re all, to a first approximation, Republicans.

  11. gVOR08 says:

    @Jen: You remind me of when I first registered for classes at Illinois. You young whippersnappers got your online registration. It was computerized, but back then if you wanted a computer you had to make your own, the Illiac II. They got an IBM 360 in, IIRC, my junior year, which meant we could get our FORTRAN run greenbar printouts back in an hour or two, rather than overnight. Registration involved standing in line at the Chemistry table to get a punch card for Chem 101, then standing in line to get a card for Rhetoric 101, and so on.

    One of the stations was a vaccination station. Used the old guns. A little jaw bit thru your skin and an air jet injected the material. Stung and left a swollen pockmark. Doing it on a mass scale, some of the operators were less than expert and might miss a vein. Saw one poor bastard holding his arm with six pockmarks down it. Don’t recall any permission slips, but this was still the era of in loco parentibus, the U could require. Wonder how the anti-vaxxers would react to that setup.