Flu shots for pregnant mothers ≠ durable protection for infants

• Infants younger than 6 months are too young for flu shots.
• To protect infants younger than 6 months, the Centers for Disease Control and Prevention (CDC) suggests that pregnant mothers get the shot instead.
• Contrary to the CDC, a study showed that flu shots only protect infants for less than 2 months after birth.

Getting the flu is something most people would rather avoid. For me, this brings to mind annual influenza vaccinations — the dreaded flu shots.

For young children, the case for giving them the flu shot is more compelling. According to the CDC, infants younger than 6 months old are at the greatest risk of serious flu-related complications.

But infants younger than 6 months are too young for the shot. For these children, the CDC advises pregnant women to get the shot instead, claiming that flu shots can protect the infant “for several months after the baby is born”.

But new evidence seems to suggest otherwise.

In a study by Dr. Nunes and colleagues, published in the journal JAMA Pediatrics, the efficacy of flu shots lasted only as long as 8 weeks.

Here’s what happened. When mothers get the flu shot, their bodies learn to recognize the influenza virus and makes antibodies against it for protection. These antibodies may be passed onto their children during birth, which protects their children against influenza, until the antibodies gradually expire.

It appears that the protective antibodies infants inherit from their mothers expire fairly quickly after birth, which may explain why the flu shot showed no protection for infants older than 8 weeks.

Bottom line

• Contrary to the CDC, a flu shot for the pregnant mother may not offer much protection against the flu for infants.
• Based on this study, infants older than 8 weeks had no meaningful protection against influenza.
• That said, it wasn’t addressed in this study but mothers may still be meaningfully protected with the shot themselves. I.e., talk to your doctor before getting or skipping your shots.
• For newborn infants, perhaps it’s better to try some of the CDC-recommended everyday preventive actions against influenza.

Source study: Nunes MC, et al. JAMA Pediatr 2016;170(9):840–7. A paid subscription may be required.

References: 1. Centers for Disease Control and Prevention. Protecting against influenza (flu): advice for caregivers of young children. Available at: http://www.cdc.gov. Accessed on September 14, 2016. 2. Centers for Disease Control and Prevention. The flu: a guide for parents. Available at: http://www.cdc.gov. Accessed on September 14, 2016. 3. Nunes MC, et al. JAMA Pediatr 2016;170(9):840–7. 4. Janeway CA, et al. Immunobiology, 5th edition. Garland Science, New York, 2001.

Photo adapted from original by dfuhlert, used under license.