Changes in vaccination policies can explain why whooping cough is seeing a historical resurgence in the United States, according to a study published Thursday.
Researchers with the U.S. Centers for Disease Control and Prevention (CDC), Imperial College London, and Monash University in Australia examined 60 years of data regarding whooping cough, or pertussis. They were searching for reasons why this highly contagious disease hit record highs in 2012.
Their study, published in PLOS Computational Biology, concluded that modern vaccines that use inactivated parts of the whooping cough bacteria aren’t as effective as previous methods. The older vaccines are more effective but don’t protect for as long.
“Pertussis has also been on the rise in several countries around the world, and we are eager to look at data from other countries to see whether the explanation for this is similar to what we found for the U.S.,” Dr. Thomas Clark, chief of the CDC’s Meningitis and Vaccine Preventable Diseases Branch, said in a press release.
Whooping cough is an infectious disease caused by the Bordetella pertussis bacteria. It infects the respiratory tract and produces a rapid cough as your body tries to expel a thick mucous produced in the branches of the lungs. Young infants are at the highest risk of developing a fatal case of bacterial pneumonia.
Whooping cough is highly contagious as it’s transmitted through airborne droplets from an infected person’s cough or sneeze. It’s cyclical with peaks in cases appearing every three to five years.
In 2012, the U.S. saw 48,277 reported cases of pertussis, the most since 1955 when 62,786 infections occurred. There were 20 deaths in 2012, the majority of which occurred among infants less than 3 months old, according to the CDC.
California experienced a pertussis epidemic in 2014 with 11,164 cases and five deaths in infants younger than 5 weeks old, according to the California Department of Public Health (CDPH). As of March 18 this year, 1,210 cases of whooping cough, including one death, were reported.
During the 2012 epidemic, Washington state had nearly 5,000 cases of whooping cough. So far this year, the state has seen 300 reported cases.
Vaccines: Historical Impact and Change
The whole-cell pertussis vaccine was introduced in the 1940s when an average of 175,000 cases of pertussis were reported.
At the time, whooping cough was a common childhood condition. However, with increased use of vaccinations over the next 50 years, the rates dropped to about 2,900 cases a year, or 1 case per 100,000 people, according to the CDC.
The U.S. saw a historical low of whooping cough cases, 1,248, in 1981. By 1983, cases had nearly doubled to 2,463. They continued to rise throughout the 1980s, particularly affecting infants and school-age children.
This coincided with media reports of children having adverse effects from whole-cell vaccinations, including becoming catatonic.
Developed in the mid-1930s, whole-cell vaccines used inactive B. pertussis cells and had up to 90 percent efficacy in three doses. The protection lasted up to 10 years. Because of safety concerns, these types of vaccines are no longer used in the United States.
Acellular vaccines — those that use purified, inactivated components of B. pertussis cells — were introduced in the 1990s and are the ones currently used today. They have around 80 percent protection for the first three doses.
The current whooping cough vaccine is combined with vaccines for tetanus and diphtheria. Called DTaP, it’s recommended in five doses beginning at 2 months of age. A booster, Tdap, is recommended for adolescents and expecting mothers.
Researchers for the new study say the level of protection provided by acellular vaccination is lower than the whole-cell vaccines, which could also explain the rise in whooping cough.
The researchers noted that increased case reporting through better diagnostic techniques and increased awareness among doctors also created a rise in data, but it was not as significant as between the former and current vaccines.
Vaccination Abstinence Linked to Outbreaks
Fears about the safety of pertussis vaccines first realized in the 1980s are similar to those about the measles, mumps, and rubella (MMR) vaccine.
Vaccination abstinence has contributed to a resurgence of preventable diseases, such as whooping cough and measles. So far this year, there have been 162 confirmed cases of measles in the U.S., 103 of which occurred in California, the CDC reports.
In California, almost 90 percent of children in day care have the required vaccinations. The largest group of children who were healthy enough to receive vaccinations but didn’t — 2.67 percent — were due to personal belief exemptions, according to the CDPH.
While the rates of whooping cough dropped in 2013, certain places with historically low vaccination rates are experiencing outbreaks of whooping cough.
These personal exemptions were partially responsible for a measles outbreak involving 147 people in seven states linked to Disney theme parks in Southern California.
In response to the measles outbreak, a bill was introduced into the California Senate that would eliminate these personal belief exemptions. It passed the Senate Education Committee on Wednesday.
In the current Washington outbreak, more than 50 of the approximately 300 cases occurred in Clark County, which has one of the highest vaccine exemption rates at 6 to 9 percent, according to the Washington State Department of Health.
“The bottom line is if people were getting their vaccines, we wouldn’t be seeing numbers like this,” Dr. Alan Melnick, the health officer for Clark County, told The Oregonian.