Whooping cough vaccine's immunity drops substantially over time
'I don't want it to put anyone off immunizing,' doctor says, as shot works to protect young babies
The vaccine to protect against whooping cough works well at first, but immunity drops off quickly, making it more important for babies to get inoculated when they're most vulnerable, Canadian doctors say.
Whooping cough, or pertussis, is a bacterial infection most commonly spread through coughing or sneezing. Anyone can get the illness, but it can be very serious for babies or people with weakened immune systems.
The number of cases of pertussis in Canada is considered low. Before the public pertussis vaccine program was introduced, the number of new cases averaged 156 per 100,000 people. In 1923, there 1,374 deaths from pertussis in Canada.
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After the vaccination program, incidence ranged from 2 per 100,000 in 2011 to 13.9 in 2012. Most of those cases are in under-immunized populations.
But there has been a global resurgence of the disease. More than 9,000 cases of pertussis were reported in California during 2010, the most in over 60 years, including 10 infant deaths, according to the state's Public Health Department. Similarly, in England, there were three deaths in infants with whooping cough confirmed in 2013, compared with 14 deaths in 2012's outbreak.
Recently, Ontario has experienced small outbreaks with no deaths.
To explore why Ontario didn't seem to have as big a problem, researchers with Public Health Ontario analyzed vaccine data for 5,867 people born between 1992 and 2013. Of these, 486 individuals tested positive for pertussis.
Receiving a newer version of the vaccine, known as acellular, was associated with twice the odds of contracting whooping cough compared with those who received the older vaccine when they were infants, the researchers said in Monday's issue of the Canadian Medical Association Journal.
"What we found out was the vaccine that we're using now, it works really well for young babies," said Dr. Natasha Crowcroft, chief of applied immunization research at Public Health Ontario. "But it doesn't last as long as we'd have hoped for. By about seven or eight years, it doesn't really seem to be giving very much protection."
Canada stopped using the older vaccine because it was associated with a higher rate of side-effects, such as fever, Crowcroft said.
Why it's important to vaccinate babies on time
"One thing that worries me about this research is that I don't want it to put anyone off immunizing their kids because what we do show is that it works really well in young infants," Crowcroft, a professor at the University of Toronto, said in an interview.
"Parents of young kids need to make sure their babies get their immunizations on time, as close to two months as they can get is the first thing, and then complete all three [doses]."
While babies are most at risk of catching whooping cough, the infection can cause coughing for weeks in adults that can lead to cracked ribs.
The researchers said the study highlights the need to re-evaluate strategies for pertussis vaccination in Canada and spur development of better vaccines.
It may also be prudent to consider vaccination in pregnancy, as recommended in the U.S. and the United Kingdom, as well as boosters later in life, they said.
In a journal commentary titled "Reining in the '100-day cough': unfinished business," Dr. Nicole Le Saux of the University of Ottawa and Dr. Ian Gemmill from the Public Health Department in Kingston, Ont., called the study a great start to tame the stubborn cough and to protect infants.
Timely, complete vaccine coverage in all age groups is the first step, the pair said.
Until newer vaccines with longer lasting protection are available, the editorial called for a rethinking of the current pertussis vaccine schedule.
"Perhaps a booster at 10 years of age should be recommended to reduce the incidence among preadolescents, or perhaps regular boosting throughout life is needed. We don't yet have a clear answer."
The study was funded by the Canadian Institutes of Health Research, the Institute for Clinical Evaluative Sciences and Public Health Ontario.