. Author manuscript; available in PMC: 2016 Oct 18.

Published in final edited form as: Lancet Respir Med. 2014 Sep 2;2(10):823–860. doi: 10.1016/S2213-2600(14)70168-7

Table 2. Causal relationships: household air pollution and the introduction of pneumococcal conjugate and Haemophilus influenzae type b vaccines.

	Mechanism	Affects

HAP affecting vaccine effectiveness or vaccine programme impact
HAP increases risk of pneumonia in a vaccinated child (eg, through impaired ciliary clearance)	Causal	Vaccine effectiveness
HAP associated with high risk of pneumonia in a vaccinated child through confounding associations (eg, poverty, overcrowding)	Confounding	Apparent vaccine effectiveness
HAP associated with lower rates of vaccine uptake through confounding associations	Confounding	Programme impact
HAP increases risk of pneumonia in an unvaccinated child who is in contact with a vaccinated child	Causal	Programme impact through indirect effects
Vaccine affecting impact of HAP
Vaccine reduces the effect of smoke exposure on carriage	Effect modification	Programme impact through direct and indirect effects
Vaccine and HAP as independent factors
Vaccine reduces the rate of pneumonia independently of smoke exposure	Independent protective effect	Vaccine effectiveness and programme impact