When babies are too young to get the whooping cough vaccine, vaccinating their parents might protect them from the dangerous infection, a new study suggests.

Young children were 51 percent less likely to be diagnosed with pertussis - also known as whooping cough - when their parents had been immunized against the infection at least four weeks earlier, compared to children in homes where parents weren’t immunized, researchers found.

The main message for parents is to get the diphtheria-tetanus-acellular pertussis (Tdap) vaccine, wrote Helen Quinn, the study's lead author, in an email to Reuters Health.

“They should make sure they are aware of current recommendations regarding Tdap vaccination in their country and follow this advice and also be aware if there is a pertussis epidemic in their local area, particularly at the time of the birth of a new baby,” wrote Quinn, from Australia's National Center for Immunization Research and Surveillance of Vaccine Preventable Diseases in Westmead.

Whooping cough typically isn't dangerous in adults, but it can make babies very sick. In some cases, symptoms may overwhelm the respiratory system and lead to death.

Infants receive their first dose of the whooping cough vaccine at two months of age, according to the U.S. Centers for Disease Control and Prevention (CDC) vaccination schedule. They don’t complete the full course of three doses until they’re six months old, however.

As a way to protect infants younger than six months old, some researchers and public health officials have called for so-called cocooning, which is the vaccination of people who often come in contact with the child.

The vaccine offered to adults as a booster shot is known as Tdap. Children receive a shot known as DTaP.

Quinn and her colleagues write in Pediatrics that there has been limited evidence on whether the cocooning method works.

For the new study, they analyzed data collected between April 2009 and April 2011 on Australian infants younger than four months, including 217 who were diagnosed with whooping cough and 585 who remained healthy.

In homes where the babies stayed healthy, 32 percent of mothers had received a Tdap vaccine at least four weeks before the data were collected. Among the babies with whooping cough, however, only 22 percent of mothers had received a Tdap vaccine. Similar results were seen among fathers.

After the researchers accounted for traits that may affect an infant’s risk of catching whooping cough, including the number of brothers and sisters, they found that vaccinating both parents is tied to a 51 percent reduced risk of whooping cough in a child under four months old.

Vaccinating the mother appeared to be especially important, reducing the risk of whooping cough by 42 percent alone. Vaccinating the fathers increased that protection to a 51 percent reduced risk.

Quinn said more research is needed to know when is the best time for parents to get the Tdap vaccine.

“In the United States, where vaccination during pregnancy is recommended, this is still the best recommendation,” she said.

The CDC says pregnant women should receive the Tdap vaccine between the 27th and 36th week. The recommendation is supported by the American College of Obstetricians and Gynecologists and the American College of Nurse-Midwives.

Quinn also said other family members and close contacts share the responsibility of keeping infants healthy.

“It is very important that other household members, such as siblings, are up to date with vaccinations, as they can also be a source of infection for very young babies,” she said.