My longtime friend has asked me to write a bit on influenza and vaccination guidelines. As medical provider, I always strive to provide my patients with as much information as possible to allow them to make the best educated choices for their children based on the latest American Academy of Pediatrics (AAP) and Centers For Disease Control (CDC) guidelines.
In order for us to understand why the flu vaccine may prevent majority of flu illness in some years and be somewhat less effective in others, I will quickly go over the fascinating flu vaccine evolution.
Influenza is a highly contagious respiratory virus. The illness is usually caused by Influenza A or Influenza B virus. The same individual can be infected with two different strains of Influenza at different time in the same season. Certain groups of children (i.e. neonates, infants, children with underlying medical conditions, children on certain medications) are at increased risk of acquiring complicated illness. Usually, in healthy children, flu causes acute, uncomplicated disease. However, it’s still a great burden on a family and a child (missed days of school and work for parents). As per CDC recommendations, the best way to prevent the flu is to get vaccinated each year.
Flu virus has a really unique ability to constantly undergo genetic change. This change is called a drift. A small change in genetic makeup occurs as the virus replicates, but still resembles the parent virus. Therefore, immune system that is exposed to similar virus will recognize it and respond. As in human evolution with generation, you become less and less genetically like from your great-great-great-great-grandparent. Same happens with influenza virus, but at significantly shorter period, genetic changes significantly altered and body’s immune system will not recognize the viruses. Thus, a person infected with a particular flu virus develops antibody against the virus. As the virus undergoes multiple replications, the antibodies created against older virus no longer recognized by the “new “virus.
When proteins found on the surface of the influenza virus change, a new sub-type is created, this is called a shift. In this situation, a person with flu vaccine will have to protection against the “novel” virus. This is usually the time when pandemic occurs. While viruses are constantly change, the shift occurs rarely. Influenza A has ability to undergo drift and shift; Influenza B virus undergoes only drift. For this reason, flu vaccines are annual and ever changing.
There are two types of flu vaccine:
- Inactivated Influenza vaccine (IIV) that is administered intramuscularly. It may be trivalent (contains two strains of influenza A and one strain of Influenza B) or quadrivalent (contains two stains of Influenza A and two strains of Influenza B).
- Live-attenuated, cold adapted influenza vaccine (LAIV), administered intranasally. LAIV comes in quadrivalent form only.
The CDC’s Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics recommend annual influenza vaccination for all children 6 month and older. Children 6 month through 8 years, should receive two doses of vaccines with one month interval in between if they did not receive 2 doses prior to July 1st, 2015. The two doses of influenza vaccine during the first season optimize immune response. Children 9 years and older receive only one dose.
The choice of vaccine depends on age and risk factors. Studies have shown the efficacy of LAIV to be greater than IIV. Thus, if the following exclusions to LAIV do not apply to an individual, it would be reasonable to recommend LAIV.
The exclusion groups to LAIV are:
- Children 6 through 23 months of age
- Children younger than five years with asthma and children two through four years of age with a history of recurrent wheezing (asthma is a precaution for children ≥5 years)
- Children with medical conditions that increase the risk for severe or complicated influenza infection
- Children who are close contacts of severely immunocompromised
There are other circumstances that are not included in the blog, which may be contradictory to receiving either form of vaccine. If you have any questions, you should contact your child’s pediatrician.
Thanks, as always!
- Centers for Disease Control and Prevention (CDC). Prevention and control of seasonal influenza with vaccines. Recommendations of the Advisory Committee on Immunization Practices–United States, 2013-2014. MMWR Recomm Rep 2013; 62:1.
- Key Facts About Seasonal Flu Vaccine
- Committee on Infectious Diseases. Recommendations for Prevention and Control of Influenza in Children, 2015-2016. Pediatrics 2015.
- Seasonal influenza in children: Prevention with vaccines