After problems with earlier samples, a fuller picture of the outbreak is emerging following another round of testing.
An estimated 263 million cases and 597,000 malaria deaths occurred in 2023.
Of 12 samples, 10 were malaria-positive, but officials continue to investigate other contributing factors.
Researchers find partial resistance to artemisinin in 11 of 100 children with complicated malaria.
The report also spotlights the urgency of vaccines for pathogens such as group A Streptococcus and Klebsiella pneumoniae, which are increasingly resistant to antimicrobials.
PAHO says it will provide countries in the Americas with affordable access to respiratory syncytial virus vaccine.
Activity has persisted beyond seasonal spikes, fueled by multiple factors including vector-control gaps, weather anomalies, and population displacement.
Since the 1970s, cases of travel-associated malaria have ticked upward in the United States.
The first phase of Nigeria's campaign will begin in November, targeting Kebbi and Beyelsa states, where malaria activity is especially high.
Researchers say the findings highlight the need for more comprehensive approaches to managing fever in children under 5 in sub-Saharan Africa.
