Reference:  Duration of Protection, Efficacy and Effectiveness

Much of the answer is in the article itself that the question references, to wit.

‘Many vaccines used today are relatively new and data concerning the length of time that they give protection is continually being updated.

For many diseases immunity wanes following natural infection.

The duration of immunity provided by vaccines varies depending on a range of factors, particularly the vaccine itself.

Live vaccines generally induce longer lived immunity than sub unit vaccines.

Sub unit vaccines frequently require primary courses and boosters.

Polysaccharide vaccines do not generate long-lived memory cells.

If the interval between doses is too short the duration of immunity can be affected. – Hence minimum intervals are required.

In the very young and very old the duration of immunity can be limited.’

The way the question is worded suggests antibodies are the be-all and end-all of protection induced by vaccines. That’s far from the case. Antibodies are just one of many diverse types of immune responses and as such have little protective utility in diseases such as tuberculosis or many viral diseases, for example.

That being said, attenuated live vaccines are much more effective compared to sub-unit and polysaccharide (1) vaccines. Typically such vaccines can replicate even if only to a limited extent, thereby providing not just a continuous source of antigen but also the appropriate inflammatory context necessary to drive and sustain antigen-specific immune responses. However, in lockstep with public demands, regulatory climate has considerably tightened since the mid-20th century, the golden age of vaccine approvals. Stance is now much more risk-averse and seeks the impossible goal of a vaccine that’s very effective but also very safe. Such a goal is impossible because an effective immune response can neither be initiated nor sustained in the absence of a damaging/inflammatory trigger. However, given the prevailing risk-averse climate, approval path for live vaccines is almost impossible. Hence most recently approved vaccines are non-live, for e.g., sub-unit.

Problem is non-live vaccines require Immunologic adjuvant, i.e., a damaging trigger to get the immune response going (2). For the longest time, Alum was the only adjuvant approved for use in humans (3). Approved long before we understood how it worked, and in fact we don’t understand fully even today, and before the current regulatory environment came into existence, alum is quite limited in its capacity to drive and sustain a broad range of immune response classes. It seems adept at driving certain classes of antibodies but not much else. This is a severe limitation because antibodies aren’t necessarily effective against all types of infectious agents, say viruses for example. Such infectious agents are better controlled by cytotoxic CD8 T cells but alum is poor at activating them. Only recently have newer adjuvants such as MF59 received regulatory approval, in newer flu vaccines for example. Based on MF59’s path to regulatory approval, these days the process for approval of a new adjuvant in a new vaccine formulation typically takes at least a couple of decades and hundreds of millions of dollars in R&D.

Vaccination’s early successes also sowed some of the seeds of its own nemesis in the form of public pressure which have sometimes driven regressive changes in vaccine formulations. As mass vaccination campaigns took hold over the 20th century, populations in countries that industrialized earlier evolved away from daily, indelible experience of avoidable deaths and disabilities due to infectious diseases (think polio for example). This process allowed a bubble mentality to take hold that could and did drive a public demand for vaccines to be impossibly and counter-productively ‘clean’, read safe. Pertussis vaccine is a poster child for how such a process unfolds (4). Still used in countries with relatively enormous populations like India, the original pertussis vaccine causes injection site reactions ranging from mild to severe. Starting in the 1980s, public campaigns against it in USA drove the development of a cleaner vaccine that’s used in countries like USA and much of Western Europe since the early to mid 1990s. Data over this period clearly shows this cleaner vaccine, acellular pertussis, is also unfortunately much less effective compared to its older, ‘dirtier’ counterpart, whole cell pertussis. Result? Pertussis is distinctly making a comeback in countries that switched to acellular pertussis vaccine.


1. Tirumalai Kamala’s answer to What is the mechanism of action of Pneumococcal conjugate vaccine?

2. Reed, Steven G., Mark T. Orr, and Christopher B. Fox. “Key roles of adjuvants in modern vaccines.” Nature medicine 19.12 (2013): 1597-1608.

3. Tirumalai Kamala’s answer to Why is there aluminum in vaccines?

4. Tirumalai Kamala’s answer to Why is the pertussis vaccine not protecting those vaccinated for pertussis?