When Jeannie Entin was pregnant, she insisted that anyone who planned to visit her newborn baby first get a booster shot to ward off whooping cough.
Entin knew the mandate would cause some eye rolling. Already, family members suspected she was reading too many pregnancy and parenting books. Most adults, meanwhile, are notoriously lax when it comes to updating vaccinations.
But pertussis, or whooping cough, is a highly contagious respiratory tract infection that can turn serious in infants. When Entin explained that adults are the most common source of the illness, she found most people were happy to comply.
"I would rather regret people thinking I'm overprotective or even a little crazy than to regret not protecting my baby," said Entin, 35, of San Jose.
In an effort to protect newborns and increase adult immunization rates, some obstetricians and pediatricians are promoting the concept of "cocooning," or vaccinating anyone who comes into contact with the infant.
"It's still rather new but catching on," said Dr. Bill Schaffner, a professor of preventive medicine in the infectious diseases division at Vanderbilt University School of Medicine.
Research suggests that newborn babies are most likely to catch whooping cough from someone in their own home.
To reduce the risk, the Centers for Disease Control and Prevention recommends that pregnant women receive a combination vaccine that contains tetanus, diphtheria and pertussis, also known as Tdap, during every pregnancy.
In studies where researchers have been able to pinpoint a cause, mothers were responsible for 30 to 40 percent of the infections in babies. The rest of the time, other people can make the babies sick, including siblings, grandparents, caregivers and those well-meaning visitors.
Cocooning alone may not be enough to prevent the illness in infants. But it can help provide indirect protection until the baby can get his own vaccine at 2 months of age. And if a pregnant woman is also vaccinated, some of the protection will cross the placenta and provide some immediate coverage, Schaffner said.
But getting everyone on board can be a challenge.
"It's difficult to have to ask," said Leah Sarago, a strength and conditioning specialist based in Fort Worth, Texas, who recently had her second child.
She planned to ask family members who might be staying with her to get vaccinated -- her parents and sister already had the booster -- but stopped short of requesting that visiting friends get immunized.
"It's hard enough to get friends and family to use hand sanitizer before touching the baby," she said.
New mom Jill Manrique, of Evanston, Illinois, had a home birth in February and asked everyone who was present during the delivery to get the Tdap and influenza vaccines. One family member didn't vaccinate her kids, leading to an awkward situation, she said. "I'm still pretty vigilant about it with visitors, both adults and children," Manrique said.
Whooping cough starts with coldlike symptoms and sometimes a mild cough or fever. As it progresses, the traditional symptoms appear: fits of rapid coughs followed by a high-pitched "whoop," vomiting and exhaustion. Infants, instead of coughing, may have an interrupted breathing pattern, or apnea.
Before the vaccine became widely available in the 1940s, about 200,000 U.S. children came down with whooping cough each year, and 9,000 died. Today, 10,000 to 40,000 cases are reported each year, with 10 to 20 deaths, the CDC reports.
Adults are a major threat to infants, even if they have a mild case. Most pertussis is thought to be spread by coughing, but transmission probably can occur even without symptoms present, Schaffner said. Once a person has it, he can spread it to 12 to 15 others, according to the CDC. About half of the infants younger than 1 with pertussis are hospitalized.
Whooping cough is cyclic in nature and peaks every three to five years. The vaccine's protection appears to fade, so many older children vaccinated as youngsters lose immunity to the bacterium.
Many adults fail to get a booster, meanwhile, due to a lack of funding, awareness and education. Last year, the standards for adult vaccination practices were revised because the rates were abysmally low. In 2012, 14.2 percent of adults older than 19 had received the Tdap booster in the previous seven years. For those living with an infant younger than 1, the rate was 25.9 percent, according to the CDC's National Health Interview Survey.
Ellie Forman, 31, said her OB-GYN strongly recommended she and her husband, Jeremy, get the vaccine. Forman then also asked her in-laws to get the booster, since she and her husband would be moving into her husband's parents' Glencoe, Illinois, home to save money.
"We haven't checked with friends, but we've kept that to a minimum in general, anyway," said Forman, whose daughter, Brooke, was born in April. "It's another thing on the to-do list, but I didn't feel like I was putting a huge burden on people because it's easy to run out to a pharmacy, and it's not expensive," Forman said.
Entin and her husband, Ari, asked potential visitors to get a Tdap booster and a flu shot in the same email that contained ultrasound pictures of the fetus. "Then we enlisted help from the grandparents to convince and remind older family members," Entin said.
When friends and family emailed or called to set up a visit, Entin asked if they had had their shot or if they -- or anyone they lived with -- had been sick in the past week. "I did trust them and didn't ask for proof (of the vaccine) though," she said. "People started reporting to me before my due date that they had gotten their flu and Tdap shots."
The Entins recognized the differing opinions on vaccines. Ultimately, however, the decision was easy. "Becoming a parent means you have to fiercely educate yourself and advocate for the well-being of your children," said Entin. "It's OK to channel your inner Mama Tiger."