4.1 vaccines

Live/attenuated vaccine

A vaccine containing a living but weakened pathogen that usually generates strong, long-lasting immunity but may pose risks for severely immunocompromised individuals.

Inactivated/killed vaccine

A vaccine containing a pathogen killed through physical or chemical processes that cannot replicate in the host but often requires boosters.

Subunit vaccine

A vaccine containing only specific isolated antigens or molecular fragments of a pathogen rather than the entire microbe.

Conjugate vaccine

A vaccine that chemically links a weak polysaccharide antigen to a strong protein carrier to induce a robust immune response.

Toxoid vaccine

A vaccine made from a neutralized bacterial toxin that stimulates immunity against the toxin rather than the bacterium itself.

Similar-pathogen vaccine

A vaccine using a safe, naturally occurring related microbe to elicit cross-protective immunity against a dangerous pathogen.

Recombinant vaccine

A vaccine produced using recombinant DNA technology to insert genes encoding specific antigens into host cells for protein expression.

Antigen

Any molecular target recognized by immune receptors that can stimulate an adaptive immune response.

Antibody

A specialized Y-shaped blood protein produced by plasma cells that binds specifically to a target antigen.

Plasma cells

Fully differentiated B lymphocytes that actively synthesize and secrete large quantities of antibodies.

Memory B cells

Long-lived B cells formed after primary infection that facilitate a rapid secondary antibody response upon re-exposure.

Helper T cells

T lymphocytes that coordinate immune responses by secreting cytokines to activate B cells and cytotoxic lymphocytes.

Cytotoxic (killer) T cells

T lymphocytes that recognize and destroy host cells infected by pathogens or displaying abnormal proteins.

Active immunity

Long-term protective immunity developed when the host's own immune system produces antibodies and memory cells in response to an antigen.

Passive immunity

Short-term immunity acquired by receiving functional antibodies generated by another individual or organism without establishing memory.

Plasmid

A small, circular extrachromosomal DNA molecule in bacteria used as a cloning vector in genetic engineering.

Restriction enzyme

A bacterial endonuclease that cuts double-stranded DNA at specific recognition nucleotide sequences.

DNA ligase

An enzyme that joins separate DNA fragments by catalyzing the formation of phosphodiester bonds.

Edward Jenner

The English physician who developed the smallpox vaccine using material from cowpox lesions.

John Snow

The English physician considered a father of epidemiology for mapping cholera cases during the 1854 Broad Street pump outbreak.

Epidemiology

The branch of medicine and public health studying the distribution, determinants, and control of health and disease patterns in populations.

Attack rate formula

$$\text{Attack Rate} = \frac{\text{Number of sick individuals}}{\text{Total population at risk}} \times 100$$

Cohort study

An observational study design that classifies individuals by exposure status and tracks them over time to evaluate disease outcomes.

Case-control study

An observational study design that selects individuals based on disease outcome and looks backward to assess prior exposures.

Herd immunity

Indirect population-level protection against infectious disease spread that occurs when a sufficient threshold of individuals becomes immune.

Hepatitis A vaccine type

Inactivated/killed vaccine.

Hepatitis B vaccine type

Recombinant subunit vaccine.

MMR vaccine type

Live attenuated vaccine protecting against measles, mumps, and rubella.

Rotavirus vaccine route

Oral administration of a live attenuated vaccine.

Polio vaccine types ($\text{IPV}$ vs $\text{OPV}$)

$\text{IPV}$ is an inactivated injected polio vaccine, whereas $\text{OPV}$ is a live attenuated oral polio vaccine.

mRNA COVID-19 vaccine mechanism

Delivers genetic instructions (mRNA) encoding viral antigen proteins for host cells to synthesize, triggering an immune response without live virus.