**7. Cocoon strategy**

For several years, the cocoon strategy, which foresees the protection of infants in the first months of life through vaccination of the mother in postpartum and of the family contacts as potential sources of infection, has been considered a promising strategy of vaccination [2].

The rationale of this approach is related to fact that the source of infection for the newborn is represented by parents (5–55% of cases), grandparents (6–8%), and siblings (up to 20%) [36, 37].

However, it is necessary to consider that the maximum immunological response to vaccination does not occur within 14 days after the administration of a booster dose and, for this reason, postpartum immunization does not allow to immediately protect the mother [38].

Anyway, the cocooning was recommended in the early 2000s in some developed countries and since 2005 by ACIP [39, 40].

This strategy has not been completely successful for several reasons [41]: the poor effectiveness, due to the large number of subjects to be vaccinated in order to prevent a single case of pertussis; the inadequate acceptance by family and close contacts of the newborn, especially if there is no pertussis epidemic ongoing (which leads to a perceived low risk); the difficulty in reaching all potential candidates for vaccination, especially if large families are involved; the high economic resources needed to implement such a program in all newborns.

A study conducted in Italy has calculated the number needed to vaccinate (NNV) within the cocoon strategy, that is, the number of people to be vaccinated in order to prevent one hospitalization due to pertussis in 1 year in children <12 months old. The NNV was very high, ranging between 5404 and 9289, depending on the considered variables [42].

The difficulties in implementing the cocoon strategy, its related high costs, and the not completely satisfactory results achieved, lead to the design of a new approach, which is currently considered the main strategy: woman's vaccination during pregnancy.
