Panel Backs Wider Pertussis Vaccination to Curb Outbreaks, Prevent Deaths

Clinicians should vaccinate caregivers and household contacts of infants with the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine (Tdap) even if the person has recently received the tetanus and diphtheria toxoids vaccine (Td) or cannot remember when they were immunized with either vaccine, according to new recommendations from a US Centers for Disease Control and Prevention (CDC) advisory committee.

The recommendations, which were made in October, are intended to give clinicians new tools to battle ongoing outbreaks of pertussis across the United States. The CDC's Advisory Committee on Immunization Practices (ACIP) also recommended vaccinating individuals older than 65 years who care for infants and children between the ages of 7 and 10 years whose vaccination history is unclear, even though the US Food and Drug Administration (FDA) has not approved a Tdap vaccine for these age groups. Both the interval recommendation and the recommendation on use in age groups that lack a vaccine approved by the FDA were made based on a unanimous vote by the committee. The CDC and the US Department of Health and Human Services usually approve recommendations made by the ACIP.

“The two recommendations are trying to address at least two issues identified as potential barriers to recontrolling pertussis,” explained Michael Brady, MD, chair of the department of pediatrics at Nationwide Children's Hospital in Columbus, Ohio, and chair of the American Academy of Pediatrics committee on infectious diseases, who attended the ACIP meeting.

Widespread infant vaccination has helped to minimize pertussis epidemics over much of the last half century. Between 1940 and 1945, there were as many as 147 000 reported cases of pertussis in the United States each year, including about 8000 deaths, according to the National Network for Immunization Information (NNII), an initiative by the Infectious Disease Society of America, the American Academy of Pediatrics, the American Nurses Association, and other clinical organizations, to provide the public with reliable vaccine information. After a pertussis vaccine was added to the Td vaccine in the mid-1940s, US cases gradually began to wane, reaching a low of 1010 reported cases in 1976, according to the NNII. However, around 2003 and 2004 public health officials began noticing a resurgence of large pertussis epidemics, according to ACIP Chair Carol Baker, MD, professor of pediatrics at Baylor College of Medicine in Houston. For example, there were about 26 000 reported cases in 2004, although the actual number of cases was probably closer to 1 million because of underreporting.

Baker explained that waning immunity among adolescents and adults who were vaccinated as infants and young children may have contributed to this resurgence. By about age 11 years, children who were vaccinated early in life become susceptible again. Unfortunately, adolescents and young adults are also very likely to spread this contagious bacterial infection because of their behaviors and their close contact with peers in school settings, she noted. Additionally, this age group has a less severe presentation of the illness, which may consist of a persistent cough for a few weeks, Brady noted. As such, they may not be recognized as having pertussis, which in young infants causes a distinct “whooping” sound after coughs. To help curb this resurgence, the ACIP in 2005 recommended vaccinating 11- to 18-year-olds with the Tdap vaccine (featuring an acellular rather than whole-cell pertussis component), which became available in 2005. However, uptake of these booster immunizations was only about 55% in 2009, which is far below the 90% coverage needed to protect the population, Baker noted.

Currently, many states are experiencing epidemics of pertussis. Among them is California, which is having its worst pertussis outbreak since the 1950s. As of late October, 6431 cases of pertussis had been reported since January, including 10 deaths among infants, who are the hardest hit by the epidemic. Infants are the most vulnerable to severe illness as a result of infection and are not yet fully protected by vaccination.

Infants get their first of a 5-dose series of a combination vaccine for infants and younger children called the diphtheria, tetanus, and acellular pertussis vaccine (DTaP) at 2 months and the last between 4 and 6 years. Nine of the infants who died in California were younger than 2 months of age, and one was aged 2 months but received the first dose only 14 days before the onset of illness.

Robert Schechter, MD, medical officer in the immunization branch of the California Department of Public Health (CDPH), explained that it is difficult to tease out the factors contributing to the current epidemic in California. He noted that cases of pertussis typically peak every 3 to 5 years and that the last peak in California was 2005. It is also too early to know whether what has happened in California may have implications for other states.

“Whether California is a leading edge [of a trend] or if there's something different going on, it's too soon to know,” Schechter said.

There are many other unanswered questions about the current resurgence of pertussis.

“It's very contagious and we don't know everything,” Baker said. “There's a lot more we need to learn about the epidemiology of pertussis and why are we seeing this now.”

To curb its epidemic, the CDPH has aggressively promoted an existing ACIP recommendation for the vaccination of parents and caretakers of young children, as well as other household contacts. It has also promoted the importance of boosters for adolescents and young adults. In fact, Gov Schwarzenegger signed a law earlier this year requiring parents to provide proof of pertussis immunization for students entering the seventh grade.

In July, the CDPH went a step further and recommended vaccinating with Tdap, off-label, in certain groups: 7- to 10-year-olds when there is a doubt about whether they were fully vaccinated against pertussis and individuals aged 65 years or older who are caring for an infant. Additionally, the CDPH recommended vaccinating individuals at risk of contracting or spreading pertussis even when there is doubt about the interval since their last pertussis or tetanus vaccination (http://bit.ly/cktnf0). Schechter explained that the aim of the recommendations is to help reduce the transmission of pertussis in the state and strengthen protection for vulnerable infants by “cocooning,” which means vaccinating their close contacts.

“We're trying to reduce the uncertainty and barriers that might keep providers from helping to protect the baby,” he said.

Now the ACIP has adopted these recommendations. Previously, the CDC had recommended using Tdap to replace 10-year boosters of the Td shot in older children and adults, but clinicians have been reluctant to give Tdap to children or adults whose vaccination history was unclear or included a more recent Td immunization. However, recent data suggest that Tdap vaccination after Td or DTaP is safe even given in intervals as short as 1 month apart (Beytou J et al. Hum Vaccin. 2009;5[5]:315-321; Halperin SA et al. Pediatr Infect Dis J. 2006;25[3]:195-200).

Additionally, because there is no vaccine approved for individuals older than 64 years, grandparents and health professionals in this age group are at high risk of becoming infected or spreading it to vulnerable individuals. But the data indicate vaccinating these individuals with Tdap is safe, Baker said. In fact, one of the 2 makers of Tdap have submitted an application to the FDA to allow marketing of the vaccine for use in these older adults.

“Giving them the vaccine looks very safe,” Baker said. She noted that the most common adverse effect with Tdap vaccination has been sore arm.

Children between the ages of 7 and 10 years have also posed a challenge to clinicians. Sometimes children in this age group do not have records that indicate whether they have received their final DTaP vaccination; in these cases, the CDPH and the ACIP recommend that clinicians give the child their Tdap booster early to ensure they are protected. Again, although this use is not approved by the FDA, the literature and the experience of other countries suggest such use is safe. For example, Brady noted that in Canada, Tdap is used to vaccinate children aged 4 years or older and appears safe. “From a pediatrician's perspective, we frequently have to catch up undervaccinated children,” he said. “This [recommendation] is very consistent with other approaches we take [to bring children up-to-date on immunizations].”

However, Baker noted that private insurance may not cover and Medicare will not cover such off-label use of the Tdap vaccine.

In California, Schechter said that it is not yet clear if 2010 represents the peak of the current epidemic. There have been fewer reported cases in some regions of the state, particularly in places like Fresno, where an uptick in cases was reported early. But the number of cases reported remains high in other areas, such as San Diego County, where the 10th fatality was recently reported.

Schechter urged physicians to stay on guard against pertussis and work to maintain high vaccination rates because fatalities have occurred even in years with fewer cases.

“We want to avoid complacency,” he said. “[Pertussis] can be a nasty disease at any age, but a fatal disease for young infants.”