A whooping cough vaccine can safely be used on seniors to protect them and others around them, including as babies, a U.S. study suggests.

Pertussis or whooping cough is highly contagious respiratory illness. Vaccines are available but immunity wanes over time.

The safety of the Tdap vaccine for seniors was unclear until now. (Jae C. Hong/Associated Press)

During the 2010 whooping cough outbreak in California, more than 9,000 cases were reported and 10 infants died. Public health units in New Brunswick, Nova Scotia, Ontario, Alberta, Yukon and British Columbia have also reported outbreaks this year.

To prevent such outbreaks, public health experts aim to create a bubble of protection around babies by ensuring that parents, siblings and other relatives are up to date in their immunizations.

Two vaccines against whooping cough are available in the U.S., but there was little data on whether they worked on people aged 65 and older. One became licensed for seniors last July.

To find out more about the safety of tetanus-diphtheria-acellular pertussis (Tdap) vaccine, Hung Fe Tsent of the Southern California Permanente Medical Group in Pasadena and colleagues compared 119,573 adults aged 65 and older who received Tdap off-label with an equal number of peers the same age who received the older tetanus and diphtheria (Td)vaccine.

The researchers found a small increased risk of inflammatory or allergic events in the first six days after Tdap vaccination but it was no more common than after Td vaccination.

The safety of Tdap for those aged 65 and older was comparable to that in the younger population.

"This study provides empirical safety data suggesting that immunizing adults aged 65 and older with Tdap to reduce the risk of pertussis in the elderly and their contacts should not have untoward safety consequences," the study's authors concluded in Friday's issue of the journal Clinical Infectious Diseases.

The researchers looked for adverse events or reactions such as meningitis, encephalitis, Bell's palsy, Guillain-Barré syndrome, allergic events and anaphylaxis.

When the researchers reviewed medical records, they found two mild cases of fever as generalized reaction and one rash after Tdap.

The researchers acknowledged they were were not looking for unexpected adverse events.

The study was funded by the U.S. Centers for Disease Control and Prevention. Several authors previously received support from vaccine makers.