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Active and passive immunity


There are two broad mechanisms by which we can acquire immunity to infections, actively and passively.

Passive immunity involves the transfer of pre-formed antibodies from an immune individual to a non-immune one.

This may occur naturally, for example the transfer of antibodies across the placenta from a mother to her baby, or artificially, for example the administration of human immunoglobulin to a non-immune pregnant woman who has been in contact with chickenpox.

In both cases the protection afforded is temporary.

Active immunity, as the name suggests, requires an individual’s immune system to be actively involved in generating the immune response and so the protection provided is generally more long lasting as immunological memory is induced.

Again, active immunity can be acquired naturally, by surviving an infection with a particular organism, or artificially, through the use of vaccines.

  • What’s the difference between innate and adaptive immunity in simple terms?

    The body’s immune system can be broadly categorised into two main types: innate and adaptive, sometimes referred to as general and specialised. The former (innate) is what we are born with, and the latter (adaptive) is what we acquire through exposure to bacteria and fungi and/or the chemicals these microbes release.

  • Are vaccines an example of passive immunity?

    ot generally but there are exceptions. Vaccines involve active immunity because when we receive a vaccine, our bodies go to work actively fighting off the microbial infection.

    However, in some cases a vaccine may contain antibodies or lymphocytes that another human or an animal has produced in response to the microbe. Babies also receive passive immunity through vaccines when they are in utero via the placenta.

  • What are the two types of immunity?

    Regarding our bodies’ own immune systems, the two types are innate and adaptive, what we are born with and what we acquire through exposure to microbes.

    Regarding how we develop immunity, the two types are active and passive. The first is when we actively develop antibodies through microbial exposure, and the second is when we passively receive antibodies through the transfer of preformed antibodies from an immune individual.

  • How many types of passive immunity are there?

    Two types, artificial and natural. Artificial passive immunity refers to the artificial (manual) transfer of preformed antibodies to a non-immune individual.

    Natural passive immunity occurs when antibodies are passed from a mother to a baby in utero via the placenta, which happens around the third month of gestation, or through breast milk.

  • Which is better, passive or active immunity?

    It’s not a case of better or worse per se, as each is useful. For example, when a patient urgently needs help fighting an infection, passive immunity acquired through the transfer of antibodies can provide critical support.

    In terms of longevity, though, active immunity affords better protection as the antibodies acquired in passive immunity only last as long as they are in circulation, which might be weeks or months.

  • Is herd immunity passive immunity?

    No, these concepts are not the same. Passive immunity is a term used to describe the natural or artificial transfer of antibodies to an individual.

    Herd immunity refers to how a population’s risk of a given disease decreases when the number of individuals immunised against that disease increases. For example, if the vast majority of a nation is immunised against measles, the infection has a difficult job spreading and infecting those who are not immunised. The herd immunity threshold varies according to the disease and how infectious it is. For measles, the estimated threshold is around 94%.

  • What are the pros and cons of passive immunity?

    It can provide critical support to an individual in need, such as someone who has been bitten by a snake.

    The transferred antibodies start working quickly, often within mere hours.
    Passive immunity can override a deficient immune system, making it useful when an individual doesn’t respond to immunisation.

    The cons include:

    Antibodies are not easy or inexpensive to produce regardless of the source (be it another human, an animal, or created in a lab).

    In some cases, antibodies from an animal can cause a severe reaction in the recipient.

    Artificial passive immunity is short-lived and restricted to the time the antibodies are in circulation.

  • What factors caused antibiotic resistance?

    Several factors have contributed, including:

    • The excessive use and misuse of antibiotics in humans and animals
    • Improper prescribing
    • Patients not finishing complete courses of a prescribed antimicrobial
    • Poor infection control measures
    • Lack of access to clean, running water
    • Poor sanitation and hygiene
  • Why is antimicrobial resistance a big problem?

    Because medication-resistant microbes are difficult and sometimes impossible to treat. The result is longer hospital stays and higher treatment costs, alongside higher mortality rates for infections that were once easy to cure, for instance, TB which is caused by the Mycobacteria tuberculosis bacteria.

    As antimicrobial resistance increases, our ability to handle common infections decreases. Some experts think we are heading towards a post-antibiotic era, in which these infections will be as deadly as they were prior to the advent of antimicrobials.

  • Is antibiotic resistance reversible?

    Probably not because bacteria evolve, which means we need new drugs to treat infections that were once easy to combat. While we may not be able to completely reverse antibiotic resistance, we can take steps to slow the process, such as limiting our use of antibiotics in humans and animals and prioritising optimal infection control systems in health care facilities.

    In addition, emerging research suggests that we may be able to tackle resistance through the use of antibiotic-resistance breakers (ARBs). These medications ‘re-sensitise’ microbes that are resistant to standard treatment options. Promising early trials have shown efficacy against the superbug Methicillin-resistant Staphylococcus aureus (MRSA).

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Using Infection Control to Combat Antimicrobial Resistance

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