Tuesday, 28 May 2013

General recommendation on vaccination

Vaccines

Toxoids, polysaccharide conjugate vaccine, recombinant subunits , live types are common variants of vaccine available. Patients' age and immune status should be considered for safe use of vaccines.
When to receive vaccines for optimal response?
I am afraid that i will get the disease so i think i should go for the vaccine. However, i had received similar vaccine 1 year ago. So should i go for it?
This has always been a question to many people. Before we can answer this question, lets understand how vaccines work.
The optimal response of the vaccines depends on the type of vaccines, the age of the patients and the immune status of the recipients.
The Advisory Committee on Immunization Practices (ACIP) General Recommendation workgroup (GRWG) revises the General Recommendation on Immunization every 3 to 5 years. It is intended to address numerous issues such as timing of each dose, screening for contraindications and precautions, the number of vaccines to be administered, interpreting and responding to adverse events.
Vaccines are usually given to members of the youngest age group at risk of the disease, and from which the efficacy and safety is demonstrated. However, vaccinations administered too close together or too young an age can lead to sub-optimal response. Therefore, it is critical for parents to understand how healthcare professionals determine when to administer the vaccines to achieve optimal response. Essentially, administration at the recommended age and in accordance with recommended intervals between doses of multi-dose antigens provide optimal protection.
Overview of vaccines
The types of vaccines available in the market include toxoids, polysaccharide conjugate vaccine, recombinant subunits vaccines, live vaccines.
·     Toxoids require booster dose to maintain antibody concentration. For example:Tetanus vaccine
·     Conjugated vaccine improves the effectiveness of polysaccharide vaccine.
·     Live vaccine usually retain immunity even if antibody titre decreases over time. Therefore, booster dose is not required. However, live vaccine like Mumps Measles Rubella (MMR) and Varicella may need a second dose because about 5-15% of those injected once do not develop immunity against the disease.
Spacing of vaccines appropriately
Any inactivated vaccine can be administered any time before or after a different inactivated vaccine or live vaccine.
2 live vaccines (nasally administered or injectable) should be administered on the same day or separated 4 weeks apart. If administered within 28 days, immune response may be impaired. An example will be Varicella and MMR, .the risk for varicella non-responders was three fold higher if given within 28 days of MMR vaccine. This rule does not apply to oral live vaccines such as oral typhoid and rotavirus.
All patients should observe the minimum intervals and ages for vaccination. The minimum intervals and ages for vaccination can be found in table 1 of Recommended Immunization Schedules for person aged 0 through 18 years published by CDC . Vaccinations administered too close together or too young an age can lead to sub-optimal response.
Another point to note is the "4 days rule" for vaccine administration
·     Vaccine doses administered less 4 days before the minimum interval or age is considered valid, except for rabies vaccine because of the unique rabies vaccine schedule.
·     Doses administered more than 5 days before the minimum interval or age is considered invalid, and should be repeated as age appropriate. The repeated dose should be spaced after the invalid dose by the recommended minimum interval.
Consider a case:
·     Varicella vaccines are recommended to give at a minimum age of 1 year old. If your child was accidentally given the dose at 9 months of age, this dose will be considered invalid. When should the child then be administered the next dose of varicella?
·     Answer: Administer when the child is one year old. Reason is because the dose is administered more than 5 days from the minimum age.
·     If the child is accidentally given the dose at 11 months and 2 weeks of age, this dose is also considered invalid. Then, when should the next dose be?
·     Answer: the next dose should be 4 weeks from the invalid dose, and in this case is after the first birthday when the child is 1 year 2 weeks old.
Spacing of live vaccines and immunologics
Oral Typhoid, rotavirus, yellow fever, zoster, and LAIV (Life attenuated influenza vaccine) can be given at any time before, concurrent or after administration of antibody containing products.
Antibody containing products are specific immunoglobulin, whole blood, packed red blood cells and plasma. Antibody containing products can reduce the immune response to measles and rubella vaccine. In general, other than the above five life vaccines, all other live vaccine should be delayed after an antibody-containing product is received. Duration of time to delay depends on the dose of the antibody-containing products received by the patient.
Spacing of inactivated vaccines and immunologics
Antibody containing products interact less with inactivated vaccines. Therefore no intervals are necessary. If the antibody containing products need to be administered at the same time as the inactivated vaccines, they should be administered at different sites.
How will taking antibiotics affect administration of vaccines?
With the exception of oral typhoid, antimicrobial agents do not affect the response to vaccines. Oral typhoid should be started 72 hours after completion of anti-microbial. Anti-microbial drugs should not be started (if possible) until 1 week after the last dose of oral typhoid.
Anti-viral drugs have no effect on inactivated influenza vaccine LAIV should be started 48 hours after completion if anti-influenza drugs. Anti-influenza drugs should not be started until 2 weeks after the LAIV.
Antiviral drugs active against herpes viruses might reduce the efficacy of varicella and zoster vaccines. Vaccines can be given 24 hours after completion of anti-viral.
What if you miss a dose of vaccine?
Vaccines should be administered as close to the recommended intervals as possible. An increase in the interval between doses do not reduce the final aees are completed. With the exception of oral typhoid, an interruption in the schedule does not require restarting the series or addition of extra doses.
How are vaccines commonly given?
·     Oral route: Rotavirus , Oral typhoid
·     Intranasal: Live attenuated influenza vaccine
·     Injectable: Intradermal. E.g. Bacille de Calmette et GuĂ©rin BCG ; Subcutaneous E.g. MMR, Varicella; Intramuscular: hepatitis B
Note that the routes of administrations should follow that of manufacturer. Inactivated vaccines containing adjuvants may cause more adverse reactions if given subcutaneously or intradermally.
Site of injection and the vaccine validity
Two vaccines can be injected at the same site, but preferably one inch apart. Variation in site of administration can result in sub-optimal response such as for hepatitis B and rabies vaccine. Hepatitis B vaccines should be given in deltoid (shoulder) muscles in adults. If it is given subcutaneously, it is invalid. Rabies vaccines should be given in the deltoid region as well and injection in the gluteal site (buttocks) is considered invalid.
How should vaccines be considered for patients with poor immune system?
Determination of altered immunocompetence is important because in certain immunocompromised patients incidence of vaccine-preventable diseases is higher which means they should be vaccinated . Yet it should be noted that live vaccines are contraindicated in certain immunocompromised patients.
·     Aspenic patients : Patients with asplenia are at increased risk of infection by encapsulated bacteria such as S. pneumoniae, N. meningitidis, Haemophilus influenza type B. Vaccination should be administered 14 days before elective surgery. If vaccines not administered before surgery, they should be administered as soon as patient stabilize to prevent infections
·     Hematopoietic cell transplant (HCT) patients: Antibody titers to tetanus, polio, MMR and encapsulated bacteria will decreases in four years if these patients are not re-vaccinated. Furthermore, influenza vaccines is recommended 6 months after HCT. Three doses of pneumococcal conjugate vaccine (Prevenar) is recommended 3-6 months after HCT, followed by one dose of pneumococcal polysaccharide vaccine (Pneumo23). Lastly, three doses of Hib vaccine is recommended 6 months after HCT. MMR is recommended 24 months after HCT