Our study showed that Olyset® Net and pyriproxyfen was successful in the control of Ae. aegypti immature stages, although seroprevalence rates were not significantly different between the trial and control areas. While more containers had immature mosquitoes in the trial area than in the control area before treatment, the number of positive containers and the number of pupae in the trial area were both less than in the control area after Olyset® Net and pyriproxyfen treatment, which suggests that the suppression of mosquitoes can be attributed to the treatments tested.
The container types favorable for Ae. aegypti immature stages can be dramatically different among local areas [36–38]. The ceramic jar was the main container to store rain water and the most important breeding container for Ae. aegypti in Tan Chanh. Compared to other provinces, the prevalence, i.e. the proportion among all the containers, and the container index of ceramic jars is higher in southern Vietnam [9, 25]. In our study, the prevalence of ceramic jars was more than 80% and its container index was 35% before intervention in the trial area of Tan Chanh. However, the prevalence and container index of ceramic jars were 30.2% and 26.0%, respectively, in Hanoi City (northern Vietnam)  and 5.9% and 16.3% in Nha Trang City (central Vietnam) [9, 25]. Thus, it is important to suppress immature stages mainly in ceramic jars as the dengue control strategy in southern Vietnam.
People in southern Vietnam store water because of the unreliable water supply and/or distaste for tap water . In many areas throughout Vietnam the contribution of poorly designed or maintained water tanks to Ae. aegypti proliferation is well recognized . However, as it is difficult to drain the heavy containers completely, a small amount of water invariably remained at the bottom of some ceramic jars in Tan Chanh, underscoring a practical difficulty, even though the jar is recognized as a breeding habitat of vector mosquitoes by the locals.
Unfortunately, most of villagers prefer not to cover their water containers, and furthermore, the government supplies insufficient number of lids for outdoor containers . Our results indicate that containers with FL lids, which ensured a complete cover over the opening, was effective in reducing the positive rate of containers with Aedes immature stages. However, more covered ceramic jars were infected with Ae. aegypti immature stages than uncovered ones located outdoors . Gravid Ae. aegypti are known to find small gaps between the lid and the lip of the ceramic jars, as seen with those that were covered by an unmodified commercial aluminum lid in four of six trials in laboratory cages . In our study, the density of pupae in containers with GL lids in the trial area was the highest in February. These results suggest that GL lids attract gravid females, which then lay eggs inside the container, as GL lids make more shade than NL lids.
In a laboratory test, Olyset® Net reduced landing attempts of mosquitoes and increased the flying time , which suggests that the Olyset® Net operates as a repellent. Our results showed that Olyset® Net reduced the number of positive containers with Aedes immature stages, which suggests that females avoided laying eggs in containers with Olyset® Net.
The percentage of properly used insecticide-treated (IT) covers was high for 5 months in the trial area in our study. A study in Cambodia shows that when about 88% of IT cover was used properly, a 58% reduction in the pupa per person index was shown at 13 weeks after treatment . Researchers did not find a significant effect of IT covers on entomological indices in north-west Venezuela because the usage of IT cover was low . In light of this study, our findings suggest that a widespread and proper use of IT covers is critical for the suppression of Ae. aegypti.
In addition to IT covers, we used pyriproxyfen, insect growth regulator (IGR), in flower vases and ant traps in the trial area. In Vietnam, people offer flowers on an altar on the first and fifteenth days of the lunar calendar. It takes 13 days for Ae. aegypti to develop in a temperature range of 20-27°C . As the average lowest temperature is 22°C in Ho Chi Minh City , adult mosquitoes may emerge before the next floral tribute. Therefore, it is necessary to add IGR to the flower vase when people change water, or the water needs to be cleaned or exchanged at least once in the 15 day interval.
Dengue infection rates among young children and women have sometimes been higher than in older children and adult males [45, 46]. Our monitoring of anti-dengue IgM and IgG in healthy residents in both control and trial area revealed seroconverted cases in both the trial and control area. A lower seroconversion rate in the trial area was evident in children 2–5 years old but there were no clear differences between the men and women of our study, which indicates that our treatment was effective on young children since they stay home most of the time. The seroconversion rates at the trial area were lower than the rates observed in the control area but not enough to be statistically significant. Further research is needed to clarify exactly how human age and gender are related to the seroconversion rate.