Plasmodium vivax infects around 14 million people with malaria each year. More than 2.2 billion people in the Asia Pacific region, the main source of infections, are at risk of this serious illness. Six countries in this region have eliminated malaria: 

• Taiwan (since 1965)
• Australia (since 1981)
• Singapore (since1982)
• Brunei (since 1987)
• Maldives (since 2015)
• Sri Lanka (since 2016).

But 22 other countries in this region are aiming to eliminate malaria by 2030, with increased political commitment, better access to diagnostics, effective malaria treatments, and bed nets. 

P. vivax remains endemic in about 40 countries across Central and South Americas, the Horn of Africa, Asia and the Pacific islands. It is co-endemic with P. falciparum in most areas, and P. falciparum causes most malaria-related deaths – which is why P. falciparum is the focus for many national malaria control programmes. 

However, P. falciparum-related deaths have fallen over the last decade, while deaths due to P. vivax have risen. This is because:

• P. vivax can be harder to detect, because it usually circulates at lower levels in the blood.
• Mosquitoes can pick up the P. vivax parasite, even when the infected person has no symptoms.
• P. vivax can remain dormant in a person’s liver, becoming active again weeks to months after the first infection to cause relapses (and recurrent malaria symptoms).

The complete elimination (radical cure) of P. vivax malaria needs a combination of drugs that work against both the blood and the dormant liver stages of the P. vivax parasite:

• Primaquine is the most widely available antimalarial drug that targets the liver stages of the malaria lifecycle, reducing the risk of relapses.
• Tafenoquine is an alternative single-dose anti-relapse treatment. 

However, primaquine and tafenoquine cannot be used without additional screening for glucose-6-phosphate dehydrogenase (G6PD) deficiency, a common genetic condition that can affect up to 40% of some populations.  People with severe G6PD deficiency are at risk of their red blood cells rupturing if given these drugs.

The lack of reliable diagnostics for this enzyme deficiency until recently means that healthcare providers have been reluctant to prescribe this treatment to P. vivax patients. What’s more, patients prescribed primaquine need to take it for 7 to 14 days for it to be effective – and it is often hard for patients to keep to this prolonged regime. 

 This means that a radical cure for P. vivax is difficult. Our inability to provide radical cure safely and effectively is one of the key factors undermining the control and elimination of the parasite.

Diagnosing resistant strains is difficult, which means that strategies to detect and track drug resistant P. vivax are limited. It is now is vital to develop better tools to assess antimalarial efficacy and drug susceptibility, so that scientists and health care workers can track emerging drug resistance, and explore novel treatment strategies.