Table 1.

Purposive sampling strategy

Key demographic characteristics	Minimum participant quota per country
Eligible chronic condition*	7 with
	7 without
Gender	8 females
	8 males
Parent/guardian of child/children under 18	4 mothers
	4 fathers
Age	8 18–49
	4 50–64
	6 ≥65
Socioeconomic group (social grade)†	7 ABC1
	7 C2DE
Adults who have had ONE of the vaccines	4 flu
	3 tetanus
Have had tetanus and flu vaccines	6
Have not had either vaccination	6
Urban/rural‡	5
Total	20

*These include asthma, chronic obstructive pulmonary disease or bronchitis, heart disease, kidney disease, liver disease, neurological conditions, weakened immune system due to conditions such as HIV and AIDS, or as a result of medication such as steroid tablets or chemotherapy.

†A=higher socioeconomic group and E=lower socioeconomic group. We used country-specific occupation and income data to determine participants’ social grade.

‡The urban/rural quotas for the UK and France were relaxed due to the quality and coverage of their public health systems.