Whooping cough vaccine effective in first years but immunity wanes significantly over time
26 Sep 2016
The vaccine for pertussis, or whooping cough, is highly effective at protecting people from the disease during the first three years after vaccination, but immunity wanes significantly over the next four years, and there is little-to-no protection after seven years, new research from Public Health Ontario (PHO) and the Institute for Clinical Evaluative Sciences (ICES) has found.
“Despite waning immunity of the whooping cough vaccine, it’s important to note that the number of cases of pertussis in Canada is still quite low,” states Dr. Natasha Crowcroft, chief of applied immunization research at Public Health Ontario and principal investigator on the study. “The most effective way parents can prevent whooping cough is to have their children immunized on time.”
The research findings are published in the Sept. 26 issue of CMAJ (Canadian Medical Association Journal). The study was conducted with PHO researchers Dr. Kevin Schwartz, lead author on the paper and infection prevention and control physician, Dr. Jeff Kwong, second author and senior scientist at ICES, as well as other scientists from PHO, ICES, the Hospital for Sick Children, the University Health Network, the University of Toronto and the University of Alberta.
Before Canada’s public pertussis vaccine program, incidence of the disease averaged 156 cases per 100,000 people. After the vaccination program began, the number of new cases ranged from 2 per 100,000 in 2011 to 13.9 in 2012. In Canada today, whooping cough outbreaks tend to be concentrated in under-immunized communities.
The current whooping cough vaccine (known as an “acellular” version) has been used in Canada since 1997 and is also used in the rest of North America, Australia, New Zealand and much of Europe. The whole cell vaccine previously used was discontinued in North America because of side effects in children such as soreness at the injection site and fevers.
The study analyzed public health laboratory data linked with population-level vaccination data for a total of 5,867 people born between 1992 and 2013, with 486 individuals testing positive for pertussis and the remaining 5,381 testing negative. The researchers found that immunity was high during the first three years after vaccination. But after seven years, there was little-to-no protection. People who received the newer acellular version of the vaccine for their first three infant vaccine doses were twice as likely to contract pertussis compared with people who had received the older whole cell vaccine when they were infants.
The older type of vaccine is still used in most of the world (in low- and middle-income countries).
“We knew that the older whole cell vaccine used in Canada was not highly effective, particularly when compared with other brands of whole cell vaccine used in the rest of the world. But we were surprised to find that babies who received one or more doses of the Canadian whole cell vaccine still resulted in better protection years later in comparison to the newer, acellular version. This finding has profound implications for understanding the effectiveness of the pertussis vaccines,” says Dr. Schwartz.
Recent studies in the United States have also found waning immunity as time elapses after immunization.
The authors say this research highlights the need to re-evaluate pertussis immunization strategies in Canada and to spur vaccine development.
Those most at risk for serious complications due to whooping cough are infants and babies, who may be too young to receive the vaccine. Current research and practices suggest the best way to protect very young infants and babies is through vaccinating infants on time and vaccinating women while pregnant, which confers some immunity protection to infants and limits the likelihood that the child will contract the illness from their mother after birth.
Ensuring that children and others in the household are immunized on time decreases the chances of infection, say the researchers. The ultimate goal, however, is to look towards a new, more effective and longer-lasting, vaccine against pertussis.