A new study finds that infants are prone to getting pertussis or commonly known as whooping cough from their siblings. Published in Pediatrics and reported in Reuters, the study said that infants are now most likely to catch whooping cough from their brothers and sisters.

Whopping cough is an extreme contagious disease caused by the bacterium Bordetella pertussis. The distinctive hacking cough followed by a high-pitched gasp for air in many patients is the reason why it is called "whooping" cough. 

In the past, it is thought that mothers are the main source of infection. According to Medical News Today, the disease can cause prolonged illness, complications and even death especially in babies under a year old.  Half of the babies in U.S. who contract the infection are said to be hospitalized.

Researchers in the new study used data collected between 2006 and 2013 from 1.306 infants across seven states. Around 25 percent were under two months. Lead author Tami Skoff of Centers for Diseases Control and Prevention (CDC) in Atlanta said, "Knowing where they're getting their disease from is important so we can target our approach accordingly." 

The new study reveals that in 36% of the cases, the siblings were the source of infection, while 21% shows mothers were accounted for the sickness. Only 10% of the data shows that fathers were the source of the cough. 

Participants were asked who had whooping cough a week or two before the infant starts coughing.  Researchers were able to identify the source of infection in almost half of the cases.  More than 60 percent points to a family member as the source of infection.

Meanwhile, this shift has not surprised the researchers.  In 2008 mothers were said to be the main source of infection however, the whooping cough has become common in older children as vaccines for whooping cough lost its effectiveness over the years. "It makes sense that we're seeing this transition from mothers to siblings as the source of infection," Skoff told Reuters Health.

So it just follows that cocooning, vaccinating the people surrounding the infant, is not effective in protecting infants from contracting the infection. Rather, researchers suggest that mothers should get the vaccine during pregnancy to pass the antibodies to the fetus. 

"You're providing direct protection to the mom and direct protection to the infant," Skoff said. Data from United Kingdom also supports this claim. "The early data is very reassuring and promising, which is why we're pushing this strategy."