Whether this particular 13-year-old’s life is in danger or not cannot be deduced from their question. However, a flu shot does not weaken one’s immune system, although those who are allergic to eggs should skip them.
The H1N1 virus, dealt with in a separate shot or nasal dose, is considered to be a risk for those who weren’t alive in 1976 when a different form of Swine Flu made the rounds, so a 13 yo is within the range of high-risk cases. In addition, asthmatics often have little lung reserve so a respiratory flu (such as H1N1, which does actual damage to lung tissue) is to be avoided.
The Centers for Disease Control’s Advisory Committee recommends that the following at-risk priority groups receive the H1N1 influenza vaccine:
• Pregnant women.
• Household contacts and caregivers for children younger than 6 months of age.
• Health care and emergency medical services personnel.
• All people from 6 months through 24 years of age.
• Persons age 25 through 64 with health conditions associated with higher risk of medical complications from influenza.
As you can see, a 13 yo is right in the high risk category, especially if they attend a public school,where they come in contact with a large number of people.
In any case, there is a certain standard of care expected of parents toward their minor offspring. If such an offspring has concerns about not getting appropriate medical care, they do have a right to tell a responsible adult, who then must refer the situation to Child Protective Services.