CDC advisory focuses H3N2v surveillance, case definitions
Recent identification of the first variant H3N2 (H3N2v) cases linked to county fairs this summer prompted the US Centers for Disease Control and Prevention (CDC) to issue a Health Alert Network (HAN) advisory today to health providers that contains the latest information about testing patients and investigating outbreaks.
The CDC said it expects that states will detect more cases and, because the number of cases could exceed those reported in 2012, it recommends a surveillance strategy designed to flag potential increases in person-to-person transmission or disease severity.
In Jul 3 H3N2v enhanced surveillance recommendations, CDC urged states to expand surveillance to include reverse-transcription polymerase chain reaction (RT-PCR) testing of specimens from ILINet providers that are collected from people who attended fairs or had contact with swine. It also suggested that states collect samples from flulike illness outbreaks in childcare or school settings, which were liked with human-to-human spread of H3N2v in 2011.
The CDC also called attention to a Jul 3 update of its H3N2v case definitions. The udpate deletes the probable case definition from its 2012 guidance and instead lists definitions for confirmed cases and cases under investigation. In the latter designation for people with flulike symptoms, close contact is defined as being within 6 feet of a confirmed H3N2v patient within 7 days of illness onset. The definition also includes recent (within 7 days) direct or indirect contact with swine or recent attendance at an event such as a fair where swine were present. Indirect contact is defined as coming within about 6 feet of a pig.
Jul 5 CDC HAN advisory
Jul 3 CDC interim enhanced H3N2v surveillance recommendations
Jul 3 CDC updated H3N2v case definitions
Study: Live intranasal vaccine may stop H3N2 from spreading in pigs
US researchers reported this week that an experimental live-attenuated swine influenza vaccine worked better than commercial inactivated vaccines in stopping the spread in pigs of an H3N2 flu strain similar to variant H3N2 (H3N2v), the virus that has been infecting some people at agricultural fairs.
The researchers say the findings suggest that vaccines like theirs could be useful for preventing H3N2v infections in people exposed to pigs. H3N2v has been associated mainly with exposure at fairs, with 309 cases reported last year and 12 so far this summer.
The investigators, from the US Department of Agriculture and two universities, note that vaccines may not block infection and pathogen transmission even when they are effective in limiting disease. They tested the efficacy of three commercially available inactivated swine flu vaccines and two experimental intranasal live-attenuated influenza virus (LAIV) vaccines in preventing infection with an H3N2 virus and subsequent transmission to other pigs. The strain they used was similar to H3N2v found in humans in 2012.
The authors found that one commercial vaccine provided partial protection as shown by reduced nasal shedding of virus; however, indirectly exposed pigs became infected, indicating that the vaccine did not prevent aerosol transmission. In contrast, one LAIV vaccine provided complete protection as shown by lack of viral replication in the lungs, and none of the indirect-contact pigs became infected.
No clinical disease was seen in either the vaccinated or unvaccinated pigs, which has been a consistent finding in pigs infected with contemporary reeassortant H3N2 swine viruses, the report says.
The authors conclude, "While vaccination with currently approved commercial inactivated products did not fully prevent transmission, certain vaccines may provide benefit for limiting shedding, transmission and zoonotic spillover of antigenically similar H3N2 viruses at agriculture fairs when administered appropriately and used in conjunction with additional control measures."
Jul 3 J Virol abstract
