View source for 22. Prevention of infectious diseases: vaccination, chemoprophylaxis

* Vaccination prevents 2-3 million deaths every year
** An additional 1.5 million deaths could be avoided with further vaccination
* Immunogenicity
** = the ability of a vaccine to provoke an immune response
** Can be measured by measuring circulating antibodies
* Protectivity
** = how well the vaccine protects against the disease
** Must be measured with long-term observational studies
* Reactogenicity
** = how many adverse reactions the vaccine produces
* Complications of vaccines
** = serious side effects
** Very rare
** Most commonly severe allergic reactions
*** Staff is trained to handle it
** The Hempt-vaccine against rabies was used until ’89, but was stopped because it caused demyelination
* Accidents related to vaccination
** Misdosage
** Inappropriate administration technique
** Using expired vaccines
** Not following the correct schedule
** Using contaminated vaccines
* “Ideal” vaccine
** 100% efficiency for all ages
** Only needs a single administration
** Does not cause side effects
** Stable under various environmental conditions
** Easily administrated (preferably oral)
** Low price
** Obviously doesn’t exist

Types of vaccines

* Live, attenuated vaccine
** The pathogen is attenuated, meaning that it is manipulated to become much less pathogenic
** The attenuated pathogen has limited ability to reproduce in humans
** Advantages
*** The closest vaccine to a natural infection
*** Provokes both humoral and cellular immune response
*** Long-term effective protection with only one or two doses
** Disadvantages
*** Can’t be given to immune compromised patients
*** Need to be continuously refrigerated
*** Small risk of the pathogen turning virulent
*** Currently very hard to make for bacteria
** Examples
*** MMR
*** Chickenpox (varicella)
*** BCG (Tuberculosis)
*** OPV (oral polio vaccine, Sabin)
* Inactivated vaccine (= killed vaccine)
** The pathogen is killed with chemicals, heat or radiation
** Advantages
*** No risk of the pathogen turning virulent (as it is dead)
*** No refrigeration needed (as it is dead)
** Disadvantages
*** Stimulates weaker immune response
*** Several doses and booster shots are necessary, requiring regular access to healthcare
** Examples
*** IPV (Salk polio vaccine)
*** HAV (Hep A)
*** Rabies
*** Influenza
* Toxoid vaccine
** Can be made for bacteria who produce toxins
** Toxin is extracted from the bacterium and inactivated with formalin, so that it is no longer pathogenic -> now called a ''toxoid''
** Used when the illness is caused by the toxin and not the bacterium itself
** Advantage
*** Rarely causes side effects
*** Stable, doesn’t require refrigeration
*** No risk of acquiring the disease
** Disadvantage
*** Several doses may be needed
*** Stimulates weak immune response
*** Do not give herd immunity
** Examples
*** Diphtheria
*** Tetanus
* Subunit vaccine
** Instead of giving the entire microbe as a vaccine, certain subunits (antigens) are given instead
** Examples
*** Hepatitis B (HBsAg)
*** Acellular pertussis (aP)
* Conjugate vaccine
** For bacteria protected by a polysaccharide capsule
** Polysaccharides are weak antigens, meaning that they stimulate weak immune responses
** The polysaccharide antigen of a bacterium is ''conjugated'' (attached to) a highly immunogenic protein antigen
** This stimulates a strong immune response against both the polysaccharide antigen and the protein antigen
** Advantages
*** Give a strong immune response with long-term protection
** Disadvantages
*** Multiple shots or booster shots may be necessary
** Example
*** Haemophilus influenzae type b
*** Meningococcus (Neisseria meningitidis)
* RNA vaccine
** The Comirnaty (by BioNTech and Pfizer) and Spikevax (by Moderna) were the first widely available RNA vaccines, but the RNA vaccine technology has been worked on for decades
** These vaccines deliver non-replicating RNA to human host cells at the injection site. The RNA encodes the spike (S) protein from the SARS-CoV-2 virus. The host cells express this RNA, producing the spike protein, against which the immune system mounts both humoral and cellular immune responses
** The RNA vaccines are safe and effective
* DNA vaccine
** Only in experimental stages
** Genes for antigens are inserted into bacteria, which produce plasmids (circular DNA) of these antigen genes
** Plasmids are inserted into the body. Cells of the body will take up the plasmids and start synthesizing the antigen from the plasmid
** The immune system recognizes the antigen produced as foreign and triggers immune response
* Recombinant vector vaccines
** Only in experimental stages
** Genes for antigens are inserted into bacteria, which synthesize large amounts of the antigen
** Antigen is then purified and given as a vaccine

Who gets vaccines:

* Age-specific compulsory vaccines
** BCG
** Haemophilus influenzas type b
** DTaP (diphtheria, tetanus, acellular pertussis)
** IPV (Salk polio)
** MMR (measles, mumps, rubella)
** Hepatitis B
** Pneumococcus
** <abbr>HPV</abbr>
* Compulsory vaccines for at-risk groups
** Tetanus
** Rabies
** Hepatitis A
* Non-compulsory vaccines for at-risk groups
** Influenza
* Job-related vaccines
** Rabies
** Meningococcus
** Tick-borne encephalitis
* Travel-related vaccines
** Yellow fever
** Cholera
** Typhoid fever
** Japanese encephalitis

Chemoprophylaxis

* Definition: Administering drugs for the purpose of preventing disease or infection
* Can be given
** Preexposure – before the exposure to the pathogen
** Postexposure – after the exposure to the pathogen but before symptoms develop
* Examples
** Giving antiretroviral drugs to people at high risk for HIV right after being exposed to HIV
*** Like health care workers who come in contact with HIV
** Giving antimalaria drugs to people before, during and after travelling to malaria-prone areas
** Giving antibiotics to people who travel to areas where Traveller’s diarrhoea (ETEC) is common
** Giving antibiotics to people who have been exposed to bacillus anthracis
** Giving antibiotics to people who have been exposed to Neisseria meningitidis

[[Category:Public health 4 - Preventive medicine]]