Is Plasmodium vivax Malaria a Severe Malaria?: A Systematic Review and Meta-Analysis

Background: Plasmodium vivax is one of the major species of malaria infecting humans. Although emphasis on P. falciparum is appropriate, the burden of vivax malaria should be given due attention. This study aimed to synthesize the evidence on severe malaria in P. vivax infection compared with that in P. falciparum infection. Methods/Principal Findings: We searched relevant studies in electronic databases. The main outcomes required for inclusion in the review were mortality, severe malaria (SM) and severe anaemia (SA). The methodological quality of the included studies was assessed using the Newcastle-Ottawa Scale. Overall, 26 studies were included. The main meta-analysis was restricted to the high quality studies. Eight studies (n = 27490) compared the incidence of SM between P. vivax infection and P. falciparum mono-infection; a comparable incidence was found in infants (OR: 0.45, 95% CI: 0.04-5.68, I-2 : 98%), under 5 year age group (OR: 2.06, 95% CI: 0.83-5.1, I-2 : 83%), the 5-15 year-age group (OR: 0.6, 95% CI: 0.31-1.16, I-2 : 81%) and adults (OR: 0.83, 95% CI: 0.67-1.03, I-2 : 25%). Six studies reported the incidences of SA in P. vivax infection and P. falciparum mono-infection; a comparable incidence of SA was found among infants (OR: 3.47, 95%: 0.64-18.94, I-2 : 92%), the 5-15 year-age group (OR: 0.71, 95% CI: 0.06-8.57, I-2 : 82%). This was significantly lower in adults (OR: 0.75, 95% CI: 0.62-0.92, I-2 : 0%). Five studies (n = 71079) compared the mortality rate between vivax malaria and falciparum malaria. A lower rate of mortality was found in infants with vivax malaria (OR: 0.61, 95% CI: 0.5-0.76, I-2 : 0%), while this was comparable in the 5-15 year-age group (OR: 0.43, 95% CI: 0.06-2.91, I-2 : 84%) and the children of unspecified-age group (OR: 0.77, 95% CI: 0.59-1.01, I-2 : 0%). Conclusion: Overall, the present analysis identified that the incidence of SM in patients infected with P. vivax was considerable, indicating that P. vivax is a major cause of SM. Awareness of the clinical manifestations of vivax malaria should prompt early detection. Subsequent treatment and monitoring of complications can be life-saving.