Dr. Matthew Kronman addresses questions about the influenza vaccine for children and families.
Thank you to Dr. Wendy Sue Swanson, a pediatrician at The Everett Clinic in Mill Creek, a member of Seattle Children’s medical staff and executive director of Digital Health, and author of the Seattle Mama Doc blog, for submitting these questions.
What is the best way to talk with parents about the effectiveness of the flu vaccine? Given that it’s only about 60% effective, why is it still an essential vaccine for children?
Influenza vaccine effectiveness varies from year to year, based in large part on the match between the strains included in the vaccine and which strains actually circulate in the community. Because vaccine composition is chosen long before we know which strains will be circulating, sometimes the match can be poor.
Even so, getting vaccinated is important for a number of reasons. First, it’s the only way to prevent influenza. It is estimated the vaccine prevented 7.2 million illnesses and 90,000 hospitalizations in the United States in 2013-2014. Furthermore, more than 100 children die in the United States each year due to influenza; most were previously healthy, and the vast majority were unvaccinated.
Second, some people – like infants under 6 months of age and those with certain medical conditions – cannot receive the vaccine, so vaccinating those who can receive it helps protect those populations by decreasing spread of flu in the community.
Finally, the vaccine is very safe. It provides the potential for great benefit and nearly no risk of serious harm.
Although moms can protect their newborns by getting the flu vaccine during pregnancy, only about 50% of pregnant women got vaccinated last year. Please explain the evidence on transplacental protection for newborns and the effects of cocooning.
All pregnant women are recommended to get the flu shot (PDF) because:
- Pregnant women are at higher risk of serious illness with the flu.
- The flu shot is safe for pregnant women and their babies.
- When pregnant women get the flu shot, their bodies begin to make antibodies that protect them from getting the flu.
These antibodies cross the placenta into the baby in the third trimester and protect the baby for the six months when they are too young to receive the flu shot themselves.
Another practice, called cocooning, may also help protect infants. “Cocooning” means to protect someone who can’t get the vaccine by surrounding them with people who did. In this instance, it means that anyone who has contact with an infant less than 6 months old should get the vaccine to protect themselves from getting the flu and passing it to the infant.
One study published in 2013 demonstrated that giving mothers the vaccine after delivery still had an impact in preventing their babies from having flu-like illnesses and fevers. Cocooning may help protect babies, but it is even better for mothers to be vaccinated during pregnancy.
Is it true that young children are prone to the flu in part because they are “flu naïve” and build immunity and cross-protection over time? If so, how can this help guide our communication with parents?
People who have been exposed to a flu virus in the past – either from the vaccine or from having a flu infection – create antibodies to protect themselves from flu viruses circulating in subsequent years. Additionally, the immune memory from a prior flu infection or vaccination can help stimulate the immune response to a new circulating flu strain, which is why older children and those who have had the vaccine in the past only need one shot each year instead of two. Because young children haven’t had as many years to build up different kinds of flu antibodies, they are more at risk of getting the flu.
The old antibodies don’t work perfectly, though, because flu genes are constantly changing. That is why we can get the flu over and over again, and why it’s important to receive a new vaccine every year.
In 2014, the Centers for Disease Control pushed for live nasal flu vaccine for kids ages 2 to 8. Evidence suggests that it provoked a better response, but the H1N1 strain last year in the nasal vaccine was ineffective. There is no specific recommendation for one over the other this year, but do you have a preference between the nasal and injected vaccines?
Generally speaking, the live vaccine should produce a better immune response in younger kids. The live vaccine helps produce antibodies secreted in the mucosa where the vaccine was delivered – the nose. In secreting those antibodies, the body prevents the flu virus from being able to take hold in the nose, where we are often first exposed. The fact that it is a live viral vaccine means that there is a little ongoing replication of the virus, which prompts the body to make a more effective immune response. This immune response tends to provide better cross-protection against strains of flu not included in the vaccine when compared with the flu shot.
Because adults have had many episodes of flu in the past, their immune systems may stop the viral replication quicker than the immune systems of younger children. This difference may also explain why the live vaccine works better in younger children.
However, last year, the live vaccine didn’t provoke an immune response for reasons that aren’t yet clear. Assuming that last year’s problems with the live nasal vaccine don’t happen again, the live nasal vaccine would generally be slightly more effective in those kids who are eligible to receive it. But, that increased effectiveness isn’t worth delaying vaccination. Patients should receive whichever vaccine is available as soon as possible in an effort to capitalize on all our opportunities for vaccination.