Studies on transmission, vaccine bring focus back to Zika

Aedes aegypti mosquito
Aedes aegypti mosquito

Mark Yokoyama / Flickr cc

Two studies published yesterday in The Journal of Infectious Diseases looked at the risk of sexual and other transmission within households in Zika-endemic areas and the value of Zika vaccination strategies.

In an accompanying commentary, Hannah Clapham, PhD, of Oxford University and the Wellcome Trust, writes that although Zika cases have dropped precipitously since the 2015 and 2016 epidemic that swept from Brazil to Miami, the disease is still a public health threat and warrants further research. 

"Zika is not gone forever. Indeed there are low levels of ZIKV [Zika virus] transmission ongoing in a number of countries, and the future potential for ZIKV to have a large impact remains unclear… We know that Zika virus has had the ability to have a large detrimental health impact, particularly through congenital Zika syndrome," Clapham said.

Sexual partners have twice the risk

The first study looked at a cohort of Zika infected patients in Puerto Rico during 2016 and 2017 and members of their households.

Household contacts, including partners, children, and other family members, answered a questionnaire and were subjected to polymerase chain reaction (PCR) and immunoglobulin M (IgM) ELISA testing for Zika virus during enrollment and follow-up at 2 and 4 months. Of 366 contacts, 34.4% had evidence of Zika infection at enrollment.

Sexual partners of known cases were 2.2 times more likely to develop subsequent Zika infection compared with household partners who did not have sexual relations with the index case (95% confidence interval [CI] for the odds ratio, 1.1-4.5). But the odds ratio was seen only with PCR testing, and not on IgM testing.

The authors also found that basic household environments contained risk factors of Zika transmission and infection. Household members were 2.5 times more likely to become infected if their homes contained open and unscreened doors and windows (95% CI of prevalence ratio, 1.5-4.1) or 2.1 time more likely if their homes had open windows and doors with screens (95% CI, 1.2-3.6).

Early vaccination could be cost-effective

In the second study, a group of researchers used modeling to determine the value of developing a Zika vaccine. During the 2015-2016 epidemic, 18 groups of scientists were actively working on a Zika vaccine. Now, according to the World Health Organization, that number is down to 7.

The authors of the study attempted to determine if developing a Zika vaccine was still economically advantageous by using a model of different vaccination strategies in Honduras, Brazil, and Puerto Rico. Different vaccination strategies included vaccinating the entire population or focusing on school-age children, young adults, or women in childbearing years.

The most cost-effective strategy identified was vaccinating women of childbearing age and young adults, the authors said, as the cost of the vaccine would be less than the medical costs incurred by a nation or territory dealing with many cases of congenital Zika syndrome.

Timing of the possible outbreak was also a factor that influenced vaccine cost. The vaccination model that was most economically valuable was one that took place 5 years before a Zika outbreak—not during the outbreak itself.

See also:

Dec 13 J Infect Dis household transmission study

Dec 13 J Infect Dis vaccine study

Dec 13 J Infect Dis commentary

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