How do COVID vaccines stimulate an immune response?

Question

UnlockIAS · Accepted Answer

Correct — C, By introducing a harmless piece of SARS-CoV-2 virus. Every COVID-19 vaccine used at scale works by showing the immune system one thing from the virus — the spike protein that studs its surface — or the genetic instructions for the body to build that protein itself. WHO's own explainer sorts vaccines into three families, and the COVID-19 vaccines occupy the second and third: those that use 'just the parts of the germ that triggers the immune system', and those that use 'just the genetic material that provides the instructions for making specific proteins and not the whole virus'. Trace India's four platforms and the pattern holds. Covishield, made by the Serum Institute of India, is the Oxford–AstraZeneca ChAdOx1 vaccine: a replication-deficient chimpanzee adenovirus, harmless in humans, carrying the SARS-CoV-2 spike gene as cargo. Corbevax and Novavax are protein-subunit vaccines — purified spike protein with an adjuvant, no virus present at all. ZyCoV-D from Zydus Cadila is a plasmid-DNA vaccine, the spike gene delivered intradermally by a needle-free jet injector in three doses. The mRNA vaccines wrap spike-coding messenger RNA in a lipid nanoparticle, and the cell reads it, builds the spike, and displays it. In none of these does a functioning SARS-CoV-2 enter the body. The immunology that follows is the same in each case: the spike acts as the antigen, the immune system makes antibodies against it and — the point of the whole exercise — leaves behind antibody-producing memory cells, so that a real infection later meets a response that is immediate rather than slow. One honest caveat: Covaxin, the Bharat Biotech and ICMR–National Institute of Virology vaccine, is a whole-virion inactivated vaccine, so it introduces the entire virus rather than a piece of it, but killed by chemical treatment and incapable of replicating. Even there, option (c) is the only defensible choice on this list, because (a), (b) and (d) each describe something a COVID-19 vaccine categorically is not.

Why the other options are wrong — (a) This is a real vaccine platform, but not the one used against COVID-19. A live-attenuated vaccine contains a living but weakened version of the pathogen — the MMR, chickenpox, shingles and oral polio vaccines are the standard examples, and WHO notes they may be unsuitable for people whose immune systems are compromised. No live-attenuated SARS-CoV-2 vaccine was deployed in India's programme or in any of the major global rollouts. The trap is Covaxin, which is indeed a whole-virion vaccine and is therefore misremembered as 'live': it is inactivated, meaning the virus has been killed with chemicals so that it cannot replicate, which WHO treats as a separate category from live-attenuated.  (b) Deliberately giving someone a functioning pathogen is inoculation of the pre-Jennerian kind, not vaccination — it would risk causing the very disease the vaccine exists to prevent. WHO states the governing principle plainly: whatever a vaccine contains, 'this weakened version will not cause the disease in the person receiving the vaccine, but it will prompt their immune system to respond much as it would have on its first reaction to the actual pathogen'. Whole-virion COVID-19 vaccines such as Covaxin use virus that has been inactivated precisely so that it is no longer real in the sense this option means.  (d) This describes passive immunisation, which is the opposite of what a vaccine does. Giving ready-made antibodies — monoclonal antibody cocktails, convalescent plasma, or the anti-tetanus and anti-rabies immunoglobulins — protects immediately but only for weeks, because the recipient's own immune system has done nothing and no memory cells are formed. A vaccine works the other way round: it supplies the antigen and makes the body manufacture its own antibodies and its own memory, which is why protection is slower to appear and far longer-lasting.

Concept: A vaccine's job is to teach the immune system a pathogen's face without letting the pathogen do any damage. WHO's account of the natural response sets the terms: a pathogen carries subparts unique to it, and the subpart that causes antibodies to be formed is called an antigen. On first exposure the body takes time to produce antigen-specific antibodies, and the person is vulnerable in the interval; once those antibodies exist they destroy the pathogen, and the body also creates antibody-producing memory cells that survive long after the infection is cleared, so a second encounter is met at once. A vaccine reproduces that first exposure using something safe. It may contain the antigen itself — a killed whole microbe, a weakened one, or an isolated protein subunit — or it may contain only the blueprint for the antigen, as DNA or messenger RNA, and let the recipient's own cells manufacture it. For SARS-CoV-2 the antigen chosen almost everywhere was the spike protein, the structure the virus uses to bind the ACE2 receptor and enter cells, which makes antibodies raised against it doubly useful: they mark the virus for destruction and they physically block the doorway.

State PCS 2023 Q18 — Science & Technology PYQ with Answer

State PCS 2023 Q18 — Science & Technology PYQ with Answer