Microbiology · Short notes

Immunology and Vaccines: Short Notes & Cheat Sheet

Innate and adaptive immunity, antibody classes, types of immunity, vaccine types, the Pakistan EPI schedule and the cold chain.

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Short notes

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Pakistan routine immunisation (EPI) schedule

Check the current provincial EPI schedule, as new vaccines are added from time to time.

The immune system

Innate immunity is immediate and non-specific (skin, phagocytes, complement, NK cells). Adaptive immunity is specific and has memory.
Humoral immunity is antibody-mediated (B cells). Cell-mediated immunity uses T cells: CD4 helper cells and CD8 cytotoxic cells.
MHC class I is on all nucleated cells and presents to CD8 cells. MHC class II is on antigen-presenting cells and presents to CD4 cells.
Antibodies: IgG (most abundant, crosses the placenta, dominates the secondary response), IgM (pentamer, first in a primary response), IgA (secretions and breast milk), IgE (allergy and parasites) and IgD (B-cell receptor).
Active immunity (from infection or vaccination) is slow to develop but lasting. Passive immunity (maternal antibodies, immunoglobulins, antitoxins, antivenom) is immediate but short-lived.

Vaccine types

Live attenuated: BCG, oral polio (OPV), measles–rubella, rotavirus, varicella, yellow fever. They give strong, long immunity but are contraindicated in pregnancy and immunosuppression.
Inactivated: injectable polio (IPV), hepatitis A, rabies, inactivated influenza.
Subunit or recombinant: hepatitis B (recombinant surface antigen), HPV.
Toxoids: tetanus and diphtheria.
Conjugate vaccines join a polysaccharide to a protein carrier so they work in infants under 2 years: Hib, pneumococcal (PCV) and typhoid conjugate (TCV).
Newer platforms include mRNA and viral-vector vaccines.

Pakistan EPI and the cold chain

At birth: BCG, OPV-0 and hepatitis B birth dose.
At 6, 10 and 14 weeks: OPV, pentavalent (DTP–HepB–Hib) and PCV; rotavirus at 6 and 10 weeks; IPV at 14 weeks.
At 9 months: measles–rubella (MR-1), typhoid conjugate vaccine and a second IPV dose. At 15 months: MR-2.
Most vaccines are stored at 2–8 °C. Adsorbed vaccines (DTP-containing, hepatitis B, PCV, IPV, tetanus toxoid) must never be frozen; the shake test detects freeze damage.
Vaccine vial monitor: use the vial only while the inner square is lighter than the outer circle.

Cheat sheet

High-yield facts in one place. Cover the right-hand column and test yourself.

Antibody classes

Class	Key fact
IgG	Most abundant; crosses placenta
IgM	Pentamer; first in primary response
IgA	Secretions, breast milk
IgE	Allergy, anaphylaxis, parasites
IgD	Receptor on naive B cells

Vaccine type → examples

Type	Examples
Live attenuated	BCG, OPV, MR, rotavirus, varicella
Inactivated	IPV, hepatitis A, rabies
Recombinant subunit	Hepatitis B, HPV
Toxoid	Tetanus, diphtheria
Conjugate	Hib, PCV, typhoid conjugate
mRNA / vector	COVID-19 vaccines

Memory aids

IgM is the 'Main first', IgG 'Goes across': IgM appears first in a primary response; IgG crosses the placenta.

Exam traps

Oral polio vaccine can be frozen at central stores, but adsorbed vaccines such as pentavalent must never freeze.
Live vaccines are contraindicated in pregnancy and immunosuppression.
Conjugate vaccines work in infants because the protein carrier recruits T-cell help.
Passive immunity gives immediate protection but no memory.

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