Wednesday, April 22, 2015

The HPAI Poultry Vaccine Dilemma


Poultry Vaccination - Photo Credit OIE


# 9967


Overnight Reuters (see U.S. could use vaccines being developed to fight bird flu in poultry) and the AP (see With bird flu spreading, USDA starts on potential vaccine) have issued reports that echo and update a story we saw from CIDRAP News several weeks ago (see USDA at work on poultry vaccine for H5N8, H5N2) – that the United States may need to reconsider its policy on the use of HPAI H5 poultry vaccines.


It should be quickly noted that any decision to use HPAI H5 vaccines in poultry is still months away, and their use would likely be limited, and targeted (as in ring vaccination around infected farms), rather than as a broad based open-ended vaccination plan. 


Throughout the United States, and indeed, most of the world, the preferred method of controlling H5 and H7 avian flu outbreaks in poultry has been immediate quarantine and the culling of infected or exposed birds. 


While vaccination may seem an easy solution to a vexing problem, the experience over the past 10 years hasn’t been entirely positive.


For some countries – mostly in Asia and the Middle East – where H5N1 has caused huge losses for a decade, poultry vaccines have long been an attractive option.  This, despite repeated warnings from the OIE that vaccination of poultry cannot be considered a long-term solution to combating  avian flu (see Does OIE recommend vaccination of animals to control the disease?)


“Any decision to use vaccination must include an exit strategy, i.e. conditions to be met to stop vaccination”. – OIE on H7N9 Poultry Vaccines.


According to 2012’s Impact of vaccines and vaccination on global control of avian influenza by David Swayne, more than 113 billion poultry vaccine doses were used from 2002 to 2010. Five countries accounted for 99% of vaccine used: 1) China (90.9%), 2) Egypt (4.6%), 3) Indonesia (2.3%), 4) Vietnam (1.4%), and 5) Hong Kong Special Administrative Region (< 0.01%).

With the exception of Hong Kong, all of these countries remain firmly entrenched with H5 viruses after more than a decade of avian flu vaccine use, and none show any signs of looking for the recommended `exit’.


While it can be argued that these vaccines have saved millions of poultry from culling, have prevented financial ruin for farmers, and has lessened food instability in developing areas of the world, there has also been a downside. 


Poultry vaccines don’t always prevent disease – sometimes they only mask the symptoms of infection, and that can not only allow viruses to spread stealthily, it can also put human health at risk.


In 2009 Professor C.A. Nidom, of the Institute of Tropical Disease, Airlangga University, Indonesia warned against relying on poultry vaccines to control Indonesia’s bird flu problem (see Indonesia: Debate Over Poultry Vaccination), while  Zhong Nanshan, a hero of the SARS outbreak and respiratory disease specialist in China, warned that vaccinated poultry can still become infected (and possibly transmit) the H5N1 virus.


Chinese expert issues new bird flu warning 2009-02-06 17:59:50

GUANGZHOU, Feb. 6 (Xinhua) -- A leading Chinese expert on respiratory diseases has warned the public to be aware that poultry can be infected with the bird flu virus but show no symptoms.

"Special attention should be paid to such animals, including those that have been vaccinated," said Zhong Nanshan.

"The existing vaccines can only reduce the amount of virus, rather than totally inactivating it," he said.

(Continue . . . )

More recently, in 2012’s Egypt: A Paltry Poultry Vaccine, a study conducted by the Virology department at St. Jude Children’s Research Hospital  looked at the effectiveness of six commercially available H5 poultry vaccines deployed in Egypt, and found only one (based on a locally acquired H5N1 seed virus) actually appeared to offer protection. 


Over the past 6 months roughly 180 Egyptians have contracted H5N1 from contact with infected poultry, and we’ve seen  reports of large numbers of poultry outbreaks – even among previously vaccinated poultry (see Egypt H5N1: Poultry Losses Climbing, Prices Up 25%).

Poorly matched vaccines, often inconsistently or haphazardly applied, have increasingly been linked to driving vaccine-escape flu variants, and may be at least partially responsible for the sudden proliferation of new avian flu subtypes we’ve seen emerge over the past couple of years (H5N3, H5N5, H5N6, H5N8, H7N9, H10N8, etc. ).


Last November the EID Journal dispatch Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China  addressed these exact concerns (bolding mine):


HPAI mass vaccination played a crucial role in HPAI control in China. However, this study demonstrated multiple disadvantages of HPAI mass vaccination, which had been suspected (13,14). For example, this study showed that H5N1 subtype HPAI virus has evolved into multiple H5N2 genotypes, which are all likely vaccine-escape variants, suggesting that this virus can easily evolve into vaccine-escape variants.

This observation suggests that HPAI mass vaccination, which is highly effective in the beginning of an outbreak, may lose its effectiveness with time unless the vaccine strains are updated. Moreover, this study showed that vaccinated chicken flocks can be infected with vaccine-escape variants without signs of illness.


Last month, in Recombinant H5N2 Avian Influenza Virus Strains In Vaccinated Chickens, which stated in its cautionary discussion (bolding mine):


In this study, three H5N2 influenza virus strains isolated from chickens were identified as novel reassortants with a highly pathogenic viral genotype. Surprisingly, the affected birds had been vaccinated with killed influenza vaccines but still showed characteristic clinical symptoms of avian influenza and eventually died.

These results are in agreement with previous work indicating that AIVs can continue genetic evolution under vaccination pressure [20]. Moreover, this study highlights the importance and necessity of periodic reformulation of the vaccine strain according to the strains circulating in the field in countries where vaccines are applied to control avian influenza.


One can’t know how things would have played out in Egypt or China had they not elected to rely so heavily on H5 avian flu vaccines, but there is enough evidence of a long-term downside to give one at least a little pause.  


The USDA has always focused on prevention and containment when it comes to H5 and H7 avian flu in this country, and it is pretty obvious they would rather not to have to go down the avian flu vaccine path if they can avoid it. 


One obvious economic downside is that vaccinated poultry may not be readily accepted by foreign markets, since it hinders testing for the virus.


But given the speed of H5’s spread this winter and its potential impact on the poultry industry, new strategies must at least be explored and considered, even those that have some potential downside to them.   


Given the less-than-sterling outcomes we’ve seen in China and Egypt with their poultry vaccination schemes - and the difficulty of `exiting’  once embarking down that vaccine road - the USDA will  have a lot they must consider before deciding on whether and what to recommend regarding the use of avian flu vaccines here in the United States.


Stay tuned.

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