Vaccines

Key examples

• Childhood vaccines
• Influenza vaccine
• Pneumococcal vaccine

 

Common indications

1. Childhood vaccines are routinely offered to all children as part of the childhood immunisation schedule.
2. Influenza vaccine is offered annually in at-risk groups including people aged over 6 months with chronic respiratory, heart, liver, renal or neurological disease; diabetes mellitus; immunosuppression; or HIV.
3. Pneumococcal vaccine forms part of the childhood immunisation schedule. It is also offered for once-only administration in at-risk groups. These are similar to the at-risk groups for influenza vaccine, but with the addition of patients aged over 65 years and those with other risk factors for pneumococcal disease (cochlear implant, risk factors for cerebrospinal fluid leakage, history of invasive pneumococcal disease, occupational exposure to metal fumes and absence of a functional spleen).

 

Mechanisms of action

• Vaccination involves administration of an antigen to incite an adaptive immune response and generate an immune ‘memory,’ usually in the form of memory B cells. 
• This facilitates a more rapid and specific immune response on re-exposure to the antigen, attenuating the severity of infection and often rendering it subclinical. 
• The antigen in vaccines may be provided as an inactivated form of the infectious agent (e.g. as in the influenza vaccine); a live but attenuated form of the infectious agent (e.g. measles, mumps and rubella [MMR] vaccine); specific protein or peptide components of the infectious agent (e.g. pneumococcal vaccine); or as a detoxified form of the exotoxin that would usually be produced by the infectious agent (e.g. tetanus toxoid vaccine).

 

Important adverse effects

• Vaccines are very safe. 
• The most common side effects are local reactions comprising pain, swelling and redness; and mild systemic effects such as fever, headache and myalgia. 
• The MMR vaccine may cause a mild measles-like illness (including a rash) about 1 week after vaccination, and occasionally a mumps-like illness (with parotid swelling) in the third week. 
• Very rarely, vaccines may cause severe hypersensitivity reactions including anaphylaxis.

 

Warnings

• Mild intercurrent illness usually does not present a barrier to vaccination. 
• Vaccines are contraindicated in patients who have had an anaphylactic reaction to a past dose or to one of its constituents. 
• Live vaccines are contraindicated in patients with significant immunosuppression, and are usually avoided in pregnancy.

 

Important interactions

• Immunosuppressive drugs (including systemic corticosteroids) reduce the immune response to (and therefore effectiveness of) vaccines, and may permit generalised infection with live vaccines.