Herd Immunity for Zika Virus?

With more cases of the Zika virus showing up in the news, the international medical community has been working towards solutions. The lessons learned from a very recent pandemic-the Ebola outbreak that peaked in 2014-could prove to be useful in determining how to best control the spread of Zika.

Proven Containment Strategy
The concept of ring vaccination, vaccinating people with a certain pathogen, their contacts, and the contacts of those contacts, has had previous successes in the public health community. It’s based on a strategy known as surveillance and containment. This style of herd immunization was responsible for eradicating smallpox, and has been used to fight tropical diseases like dengue fever and the chikungunya virus. An experimental Ebola vaccine was tested using ring vaccination.

Ira Longini, PhD, professor and co-director, Center for Statistics and Quantitative Infectious Diseases , Emerging Pathogens Institute at the University of Florida, Gainesville, who presented on the Ebola vaccine earlier this month at the American Association for the Advancement of Science’s annual meeting, remarked, “For any infectious disease transmitted through person to person contact, you see very clustered transmissions.” With Ebola, in the three West African counties where it was most prevalent, only 0.13% of the entire populations contracted the virus. Yet localized transmissions were very high. By vaccinating people in those clusters, public health workers were able to concentrate the vaccine where it was most needed and where it would have the greatest impact.

Lessons from Ebola could soon apply to the Zika outbreak. Hawkey-Nene Aminata Diallo and Gamou Saiman Gaston, from the World Health Organization Ebola vaccination team, carefully go through the consent process with a participant in the Ebola vaccine trial. Photo courtesy of the University of Florida.

Lessons for Zika
Since Zika is carried by localized mosquitos and has a high transmission rate, ring vaccination could be an effective containment plan. “The rings could consist of family members and members of your neighborhood,” said Longini. “It could be a good strategy for creating rapid and effective phase three trials for a Zika vaccine.” With conventional, random, blinded placebo-controlled vaccine trials, many people in the trial are never actually exposed to the disease, so the vaccine does not have the most bang for its buck.

 

“A reasonable strategy is needed,” said Longini of the Zika virus. He estimates there could be human safety and immunogenecity trials for a vaccine in 12-18 months. The public health community is moving as fast as safely possible. Just a short while ago, the educated guess was three to five years for a vaccine, now that time frame has shrunk. Longini explained, “It depends on how dedicated and fast the international public health community and pharmaceutical companies are in being engaged.”

Most of the current research centers on vaccines with live viruses. One complication is that cases of Guillen-Barre syndrome have shown up in people with Zika. That could potentially impact immunization going forward.

Zika is especially concerning to women because of the links to birth defects, like microcephaly. Since roughly 80% of infected people are asymptomatic, developing a preemptive containment strategy is paramount. One day, all women of childbearing age could be immunized against Zika as part of the routine vaccination schedule for girls.

SEE ALSO: Poll: Zika Virus Preparation

Preparing Nurses
Longini cautioned, “Vaccines are not totally harmless. You don’t have to vaccinate everybody. Vaccinate those at risk.”

One of those groups at potential risk for Zika are frontline healthcare workers, like nurses. “By definition, healthcare workers are the contacts of cases,” said Longini. In the ring vaccination theory, pre-emptive immunization of nurses and other medical professionals could be part of the strategy. “You might want to vaccinate before there are any cases,” Longini recommended. Especially if the microcephaly connection grows more evident, which he strongly guesses it will, “Female frontline workers of childbearing age would want to be vaccinated.”

He continued, “Nurses are well trained in barrier protection,” when it comes to infection prevention. “A vaccine is just another layer of protection.”

Danielle Bullen is on staff at ADVANCE. Contact: dbullen@advanceweb.com

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