# 7828
This is the second of two posts on yesterday’s updated CDC guidance on the use of antivirals with avian H7N9. The first post looked at Guidance For Antiviral Treatment, while this post will concern itself with post-exposure chemoprophylaxis.
There are basically three uses for antivirals:
- Treatment of those infected
- Outbreak Prophylaxis for people who are likely to be exposed (First responders, HCWs, etc).
- PEP (Post Exposure Prophylaxis) - giving antivirals to those exposed, but not yet symptomatic to prevent infection
PEP (Post-Exposure Prophylaxis) – is a short course of antivirals given to people who have been exposed to virus, but who have not come down with the illness. The idea is, if you can inhibit the replication of the virus in the exposed person, you can prevent subsequent infection.
This tactic has been used sucessfully with poultry cullers working with H5N1 infected birds in Indonesia, India, and Bangladesh. In the past medical personnel, exposed family members, and sometimes entire neighborhoods in Indonesia, China, and Turkey have received antivirals prophylactically to suppress the spread of the H5N1 virus.
In 2008, In the HHS's Proposed Guidance on Antiviral Drug Use during an Influenza Pandemic, the concept of HOUSEHOLD PEP was discussed, but the idea was never officially endorsed. Given the relative mildness of the 2009 H1N1 pandemic, the use of chemoprophylaxis was limited – particularly in the United States - but we do have a few studies to look at..
One of those, from 2010, was featured in CIDRAP NEWS: On Two NEJM Pandemic H1N1 Studies where we saw the following report:
Studies examine H1N1 spread in military units, households
Robert Roos
News Editor
Jun 9, 2010 (CIDRAP News) – When the H1N1 pandemic influenza began hitting Singapore's military forces last summer, health officials largely arrested its spread by giving oseltamivir to everyone in the affected units, in combination with other preventive steps, according to a report released today.
Among 1,175 soldiers in four settings, 75 were infected before the preventive steps were taken, and only seven became infected afterward, according to the report in the New England Journal of Medicine (NEJM). The findings suggest that antiviral "ring prophylaxis," along with quick identification and isolation of infected people, can be effective in halting outbreaks in "semiclosed" settings, the researchers said.
The Singapore study is valuable because it proves that ring prophylaxis (or PEP) apparently can work to slow down or contain an influenza outbreak in a closed or semi-closed setting. It also bodes well for the effectiveness of Outbreak Prophylaxis among medical personnel, although there remain open questions on the wisdom of taking antivirals for weeks or perhaps months at a time.
But to add a wrinkle, the second study in the CIDRAP report suggested that patients infected with novel H1N1 who were treated with Tamiflu produced lower levels of antibodies than those who went untreated, opening the possibility that they might be at risk for re-infection
There are also legitimate concerns that the indiscriminate use of antivirals could hasten the emergence of resistant viral strains. Still, Chemo-prophylaxis would likely have an important role in any emerging influenza pandemic.
It’s primary value would be to halt or contain initial small outbreaks, during a time when a pandemic virus is not circulating widely. Hopefully buying time for the development of a vaccine and the production of additional antiviral medications.
Given the finite supply of antiviral drugs (and the possibility that serious infections might need double the dose for double the time), once a pandemic virus is circulating widely, the best use of antivirals would be for treatment.
Here then are some excerpts from the CDC’s new guidance on Chemoprophylaxis against exposure to the H7N9 virus. Follow the link to read it in its entirety.
This document provides interim guidance to help clinicians determine when influenza antiviral agents should be used for chemoprophylaxis of close contacts of confirmed or probable cases of human infection with avian influenza A (H7N9) in the United States. (H7N9 virus updates are available at Avian Influenza A (H7N9) Virus). These recommendations are based upon expert opinion and currently available published and unpublished data for antiviral treatment and chemoprophylaxis of seasonal, pandemic, and zoonotic influenza. This guidance will be updated as additional information on H7N9 virus epidemiology and transmissibility becomes available.
These interim recommendations are based upon available information and the following considerations:
- There is no available H7N9 vaccine at this time.
- This virus has caused severe disease and substantial mortality among detected H7N9 cases to date.
- Limited, non-sustained human-to-human H7N9 virus transmission cannot be excluded in some case clusters in China.
- Sufficient supplies of antiviral agents that are expected to be effective against H7N9 are available.
The public health goal of this interim guidance is to prevent further spread of H7N9 if there is introduction/travel of infected persons into the United States. It is specific to a scenario where there are sporadic H7N9 cases associated with poultry exposure and possible limited, non-sustained human-to-human H7N9 virus transmission in China. This guidance will be updated if circumstances change.
Definition of Close Contacts
Close contacts are defined as persons within approximately 6 feet (2 meters) or within the room or care area of a confirmed or probable H7N9 case patient for a prolonged period of time, or with direct contact with infectious secretions (such as being directly in the path of a sneeze) while the patient was likely to be infectious (beginning 1 day prior to onset of signs and/or symptoms and continuing until resolution of illness). 1
In general, decisions to initiate antiviral chemoprophylaxis should be guided by the risk stratification described below,2 based on observational data for reported cases of human infections with H7N9 and H5N1 viruses, and on data from seasonal influenza studies.
- Highest-risk exposure groups (greatest possible risk of transmission)
- Household or close family member contacts of a confirmed or probable case
- Moderate-risk exposure groups (unknown risk of transmission)
- Health care personnel with higher-risk contact with a confirmed or probable case (e.g., during bronchoscopy or intubation; or while performing tracheal suctioning, delivering nebulized drugs, or handling inadequately screened/sealed body fluids without use of recommended personal protective equipment (PPE); or with a recognized breach in PPE procedures)
- Low-risk exposure groups (transmission unlikely)
- Others who have had social contact of a short duration with a confirmed or probable case in a non-hospital setting (e.g., in a community or workplace environment)3
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Post-exposure Chemoprophylaxis of Asymptomatic Close Contacts
- Oseltamivir or inhaled zanamivir chemoprophylaxis should be provided to close contacts of a confirmed or probable H7N9 case patient according to risk of exposure.
- In high-risk exposure groups, chemoprophylaxis should be administered.
- In moderate-risk exposure groups, chemoprophylaxis could be considered.
- In low-risk exposure groups, chemoprophylaxis is not routinely recommended.
- Decisions to initiate antiviral chemoprophylaxis for persons in moderate- and low-risk exposure groups should be based on clinical judgment, with consideration given to the type of exposure and to whether the close contact is at high risk for complications from influenza (see Influenza Antiviral Medications: Summary for Clinicians).
- Administration of chemoprophylaxis should begin as soon as possible after first exposure to the confirmed or probable case.
- The treatment dose for neuraminidase inhibitors (two doses per day) is recommended instead of the typical chemoprophylaxis regimen (1 dose per day). For dosage recommendations for treatment by age group, please see Guidance on the Use of Influenza Antiviral Agents: Dosage.
