Dear Dr. Roach: I’ve read that there’s a big increase in whooping cough. I am pregnant and want to know the best way to protect my baby. Is it exclusive breastfeeding? Getting the vaccine? Making sure that visitors are vaccinated or wear masks? — D.G.

Answer: Whooping cough is caused by a species of bacteria called Bordetella pertussis. This causes a respiratory infection that can be very serious in infants, with over 80% of the youngest babies needing hospitalization. You are right that there have been massive increases in the risk of this infection during the past two years. An infant normally receives a pertussis vaccine at 2 months, although it can be given as early as 6 weeks in an outbreak setting.

The most important way for a pregnant woman to protect her baby from pertussis before the baby can be vaccinated is to get vaccinated herself during the second trimester of pregnancy. This vaccine is recommended for all pregnant women for every pregnancy, even if they’re already vaccinated.

This is more to protect her baby than to protect her, since the antibodies she makes after the vaccine will be transmitted across the placenta. This gives her baby 80% to 96% protection against whooping cough during the critical period before the baby can be vaccinated. Although breastfeeding has many benefits, the evidence that it protects the baby against whooping cough is weak, with a large study showing minimal benefit.

It’s a good idea to keep people who are sick away from your baby. If this isn’t possible, they should wear a mask and wash their hands. Unfortunately, making sure that visitors are vaccinated, although reasonable, wasn’t as effective as we hoped.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYour

GoodHealth@med.cornell.edu.