BACKGROUND : Despite high levels of naturally-acquired immunity (NAI) within local communities in malaria high
transmission settings in Africa, such people often experience clinical disease during peak transmission months due to
high parasite challenge. Major recruiters of unskilled labour in high-transmission malaria settings in Africa generally
withhold chemoprophylactic medication from this large component of their labour force, which if administered during
peak “malaria season” could reduce incidence of clinical malaria without unduly affecting NAI.
COMMENTARY : Naturally acquired immunity confers protection against severe clinical disease and death, but does
not prevent mild clinical disease and, therefore, still results in worker absence and worker debilitation. Evidence exists
that NAI persists despite periodic parasite clearance and therefore provides opportunity for drug prophylaxis during
peak transmission months, which contributes to broader malaria elimination objectives, community well-being, and
reduced absence from work. Such chemoprophylaxis could be by way of standard daily or weekly supervised administration
of prophylactics during peak transmission months, or occasional intermittent preventive treatment (IPT), all
aimed at reducing parasite burden and clinical disease. However, challenges exist regarding compliance with drug
regimens over extended periods and high parasite resistance to recommended IPT drugs over much of Africa. Despite
withholding chemoprophylactics, most large companies nevertheless pursue social responsibility programmes for
malaria reduction by way of vigorous indoor residual spraying and bed net provision.
CONCLUSIONS : The lack of clear understanding regarding functioning of NAI and its role in malaria elimination
campaigns, concerns about drug resistance and appropriate drug choice, lack of studies in the use of IPT in people
other than pregnant women and small children, plus lack of guidance regarding drug options for IPT in the face of
widespread resistance to sulfadoxine–pyrimethamine, means that large contractors in malaria endemic settings will
likely continue to withhold malaria prophylactic drugs from locally-recruited workers, with adverse consequences on
workforce well-being. Nevertheless, if the point of chemoprophylaxis is to reduce clinical malaria by way of reducing
parasite challenge without significantly impacting NAI, then a comparable result can be achieved by implementation
of effective vector reduction programmes which minimize parasite transmission but maintain NAI.