Based on the available evidence of the impact “cocooning” has on transmission of pertussis to infants, no changes are currently recommended in the use of Tdap vaccine for close contacts of infants, Jennifer Liang, D.V.M., said at a meeting of the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices.
Presenting the conclusions of ACIP’s pertussis vaccines work group review on the impact of cocooning strategies, Dr. Liang, the CDC’s lead member of the work group, said that pertussis vaccination programs should be focused on vaccinating women during every pregnancy, maintaining high levels of DTap coverage, sustaining Tdap coverage in adolescents, and improving Tdap coverage in adults.
In 2005, ACIP recommended the “cocooning” strategy: vaccinating with Tdap for all close contacts of infants under age 12 months to reduce the risk of transmitting pertussis, including parents, siblings, grandparents, child care providers, and health care personnel, in addition to vaccinating pregnant women immediately post partum. In 2011, ACIP recommended Tdap during pregnancy for women who had not previously received the vaccine, or a postpartum dose for women who did not receive the vaccine during pregnancy and had not previously received the vaccine. In 2012, the recommendation was expanded to every pregnancy, whether or not the woman had received the vaccine before.
The optimal strategy to prevent the transmission of pertussis is vaccinating women during pregnancy, which has been shown to be highly effective in reducing transmission to infants, but rates of vaccination in pregnant women have not been high, said Dr. Liang, an epidemiologist in the CDC’s National Center for Immunization and Respiratory Diseases.
Rates of Tdap coverage, however, among pregnant women in the United States have ranged from 14% to 23% in studies using different sources, including a Michigan Medicaid study, she said.
Implementing and sustaining cocooning programs remain a challenge. Although uptake of Tdap has been highest in postpartum women, there has been limited success in vaccinating fathers or other family members, she said, noting that, in 2012, the rate of Tdap coverage among adults aged 19-64 years who reported living with an infant under age 1 year was 26%.
The effect of cocooning in preventing infant pertussis also is “unclear and inconclusive,” and evidence of the effectiveness of the postpartum dose in preventing infant pertussis is limited and the data are conflicting, Dr. Liang said. Another issue is that, over the past decade, the source of transmission to infants has shifted from parents (usually mothers) as the most common source to siblings, who have more recently been identified as the most common source, she said. A CDC study determined that, between 2006 and 2013, family members were the source of the infection in 66%-85% of infant pertussis cases in which the source of infection was known. Siblings were the most common source, linked to almost 40% of cases.
“Even if additional Tdap doses are recommended, this would not address the observed shift to siblings as the source of pertussis to infants and puts greater emphasis on the importance of providing newborns with antipertussis antibodies, and there is an optimal strategy in place – vaccinating women during pregnancy,” she said.
This message is emphasized in a recently launched CDC campaign to improve Tdap vaccination rates during pregnancy, which includes fact sheets for health care professionals that point out that Tdap during pregnancy provides the best protection for infants, postpartum Tdap administration is not optimal, and “cocooning alone may not be effective and is hard to implement.”
Several meeting participants pointed out that vaccine uptake during pregnancy is higher in settings where the vaccine is available on site, as high as 80%-90% of pregnancies, and that having to get the vaccine outside of the office, such as at a pharmacy, can markedly reduce the likelihood of vaccination. The CDC’s updated materials, including fact sheets and posters, are available for health care professionals at http://www.cdc.gov/pertussis/materials/hcp.html.
A single dose of Tdap is recommended for people aged 11-64 years: one dose is routinely administered at age 11 or 12 years and one dose of Tdap is recommended for pregnant women during every pregnancy. DTaP vaccine is used to vaccinate younger children starting at age 2 months and is not licensed for adolescents, adults, or children 7 years of age and older.