The main purpose of this study is to evaluate immune persistence at 30 and 36 Months of Age and Pertussis Breakthrough Infections between 19 and 36 Months of Age following two regiments of DTaP-IPV/Hib Pentavalent Vaccine in Healthy 2-Month-Old Infants and Children in China.

This study was based on the DTaP-IPV/Hib Pentavalent Vaccine Basic Immunization Strategy Optimization Study Cohort ("Pentavalent Vaccine Cohort") and the Epidemiological Investigation of Carrying Status of Pathogens Causing Acute Respiratory Infections (ARIs) in Infants and Young Children Cohort ("Pathogen Surveillance Cohort").

DTaP-IPV/Hib vaccine basic immunization strategy optimization study is a single-center, randomized, prospective and open clinical trial. The study was designed for two groups: 2, 3, 4, 18 months of age (control group) and 2, 4, 6, 18 months of age (intervention group). Subjects were randomly assigned to two groups according to the principle of informed consent. Collect basic demographic information of children and their families. The control group received 3 doses of acellular DPT vaccine at 2, 3 and 4 months of age respectively, and 1 dose at 18 months of age; The intervention group received 3 doses of acellular DPT vaccine at 2, 4 and 6 months of age respectively, and 1 dose at 18 months of age. The immunogenicity and safety were observed before and after 28 days of 3 doses of basal immunization, and after 28 days of enhanced immunization at 18 months of age.

The pathogen surveillance team included 2-month-old infants and caregivers with whom they shared a life history. After informed consent, the researchers followed up the subjects from 2 months of age to 19 months of age. The main contents of the visit are sample collection and unified questionnaire survey.

On the basis of the surveillance of ARI aged 2 to 19 months, follow-up was conducted for 17 months. During the follow-up period, ARI telephone visit was conducted twice a week. After ARI was found, pathogen sampling and testing were conducted for them (participants and their caregivers) to monitor the emergence of pertussis infection. Blood samples and throat swabs were collected at 30 and 36 months of age (caregivers were also required to take simultaneous samples), and penta vaccine immunity persistence was observed and multiple respiratory pathogens were monitored.

Inclusion Criteria:

- (1)Received 4 doses of DTaP-IPV/Hib pentavalent vaccines (2) Obtained consent from the participant's caregiver and sign an informed consent form

Exclusion Criteria:

-(1) Diagnosed by a physician with a coagulation abnormality (e.g., coagulation factor deficiency, coagulopathy, platelet abnormality) (2) Any other factor considered to make participation in the trial unsuitable.