Vaccination FAQs
출처 : http://www.animalhealthaustralia.com.au/programs/eadp/ausvetplan/fmd-response-policy-review/vaccination-faqs.cfm
1. Are there FMD control options other than stamping out?
Yes. Especially since the FMD outbreak in the United Kingdom in 2001 when almost 6 million cattle were culled, research into FMD has offered alternative options, such as protective vaccination, for responding to an outbreak of FMD.
The FMD outbreak in the United Kingdom in 2001 was the largest in history. The UK eradicated FMD by stamping out the disease, but suffered losses of more than eight billion pounds sterling (approximately A$19 billion); the country’s livestock and tourism industries were devastated as a result.
In the same year, Uruguay also suffered an outbreak of FMD. Uruguay’s cattle population was the same as that of the UK and the number of infected herds was almost identical. However, while the UK used stamping out on its own and killed a total of 5,730,000 cattle (with 3,910,000 testing positive to FMD), Uruguay used protective vaccination (‘vaccinate to live’) to assist its eradication campaign and needed to kill only 6,937 cattle (all FMD positive).
The direct cost of the FMD outbreak in the UK was US$4.6 billion, that of Uruguay US$13 million. The total economic impact of the FMD outbreak in the UK was over US$10 billion, that of Uruguay less than US$400 million.
2. Why would vaccination be considered in an FMD outbreak?
Vaccinating animals can ‘buy some time’ because it can delay or even prevent further spread of disease from the known outbreak locations.
The Australian response policy for an outbreak of FMD is to control and eradicate the disease through stamping out. Time is the essence here; if there are delays in carrying out the slaughter, the effectiveness of this approach is not guaranteed, and the disease can spread out of control.
There are two principal options for vaccination: protective vaccination (‘vaccinate to live’) and suppressive vaccination (vaccinate to die’). For their respective advantages and disadvantages see relevant questions.
3. What does ‘vaccinate to live’ mean?
‘Vaccinate to live’, more appropriately called ‘protective vaccination’, means that an animal is vaccinated against a disease for the purpose of protecting it from getting ill and possibly dying. If used as part of an FMD eradication campaign, protective vaccination greatly reduces livestock losses because fewer animals get sick or need to be killed.
Protective vaccination is what is commonly used to protect people and animals from infectious diseases, e.g. measles, influenza, tetanus. People and animals are vaccinated when they are healthy, as a measure to prevent a future infection. In an FMD outbreak, ‘ring vaccination’ would be used, that is healthy animals in a, for example, 5 km radius around an infected premises would be vaccinated to provide a ‘buffer population’.
4. What does ‘vaccinate to die’ mean?
‘Vaccinate to die’, more appropriately called ‘suppressive vaccination’, has the purpose of minimising or stopping virus shedding and ‘buying time’ in the eradication campaign. It may protect the animal against clinical disease, but it will not necessarily prevent infection.
Animals to be vaccinated under this strategy are usually those at high risk of infection, literally the ones in the middle of the outbreak. If suppressive vaccination is used as part of an FMD eradication campaign, all vaccinated animals will be killed at the end of the eradication campaign.
5. How would we use vaccination? For example, would all susceptible animals be vaccinated?
The exact vaccination strategy would depend on the circumstances of the outbreak but the key parameter would always be to quickly and effectively control the outbreak with a view to restoring business continuity.
Typically, if suppressive vaccination (‘vaccinate to die’) is used, animals to be vaccinated are those at high risk of infection, literally the ones in the middle of the outbreak. This is because the purpose of suppressive vaccination is to ‘buy time’ in the eradication campaign, that is to ‘suppress’ the spread of infection.
If a strategy of protective vaccination (‘vaccinate to live’) is followed, ring vaccination is typically used. This means that animals within a certain radius around infected premises are vaccinated so that a buffer population of vaccinated animals surrounds the infected premises, helping contain the outbreak and prevent it from spreading to the outside of the ring.
6. Why do vaccinated animals need to be killed if suppressive vaccination is used as part of an FMD eradication campaign?
Depending on the time between vaccination and infection, vaccinated animals may not show clinical signs, but they may still carry the virus. That is why even those vaccinated animals are ultimately killed.
The purpose of suppressive vaccination is to ‘buy time’ in the eradication campaign, that is to ‘suppress’ the spread of infection. Animals to be vaccinated under this strategy are usually those at high risk of infection, literally the ones in the middle of the outbreak. If they’re not infected already, they’re expected to become infected. Depending on the time between vaccination and infection, they may not show clinical signs, but they may still carry the virus. That is why even those vaccinated animals are ultimately killed.
Emergency vaccination of at-risk stock (suppressive vaccination, ‘vaccinate to die’) may result in the need to destroy animals that would otherwise have avoided destruction in a conventional stamping-out approach.
7. What are the advantages and disadvantages of protective vaccination in an FMD outbreak?
One advantage is that – while eradication is still achievable and remains the goal – far fewer numbers of healthy animals need to be killed to achieve eradication, reducing not just livestock losses but also collateral damage to e.g. commercial activity in rural locations. On the downside, concern is sometimes expressed that the use of protective vaccination doubles the waiting period required to regain the OIE status of FMD free country when compared to stamping out or stamping out with suppressive vaccination (6 months versus 3 months).
Using protective vaccination as part of the eradication campaign also means there are fewer resources required to kill animals and safely dispose of the carcases.
Not having to kill large numbers of healthy animals would attract wide community support.
Regarding regaining freedom from FMD, in reality, the OIE does not determine the length of trade exclusion. The point in time following eradication of FMD when export trade resumes will be determined between Australia and its trading partners; regardless what eradication strategy is chosen, exclusion of some commodities from some export markets will most likely last for at least 12 months.
8. Has protective vaccination ever been used effectively in an FMD outbreak?
Yes, for example by Uruguay in 2001, the same year that the UK had an FMD outbreak and used stamping out on its own. The Uruguay outbreak lasted 18 weeks, half as long as the UK outbreak, and the total economic impact was less than 4% of that in the UK.
Uruguay’s cattle population was the same as that of the UK at the time of the 2001 outbreak and the number of infected herds was almost identical. However, while the UK used stamping out on its own and killed a total of 5,730,000 cattle (with 3,910,000 testing positive to FMD), Uruguay used protective vaccination to assist its eradication campaign and needed to kill only 6,937 cattle (all FMD positive).
The direct cost of the FMD outbreak in the UK was US$4.6 billion, that of Uruguay US$13 million.
The total economic impact of the FMD outbreak in the UK was over US$10 billion, that of Uruguay less than US$400 million.
9. Does Australia have FMD vaccine available?
In Australia, governments and livestock industries have invested in FMD vaccine supply arrangements.
A supply contract with a commercial manufacturer has been secured over 5 years (ending in 2014) to provide 500 000 cattle-equivalent doses of any of nine FMD strains within 7 business days of notification. This number of doses has been calculated to be sufficient in the early stages of a response but will be supplemented by further purchases if needed.
10. What are ‘DIVA tests’?
DIVA stands for ‘Differentiating Infected from Vaccinated Animals’.
If animals are vaccinated against FMD, they will – for a period of time – give a positive result in blood tests. However, the animal could also be infected with ‘real’ FMD virus. Standard tests cannot tell the difference between a positive result due to vaccination and a positive result due to actual FMD infection.
FMD DIVA tests are tests that can determine whether an animal that tests positive to FMD screening tests does so because it is infected with FMD virus or because it is vaccinated.
11. What is the relevance of ‘DIVA’ testing for FMD vaccination?
DIVA tests are needed to demonstrate FMD disease freedom after an FMD outbreak has been eradicated when protective vaccination has been part of the response.
Before we can claim success that we have eradicated an FMD outbreak, we need to demonstrate that there are no animals left that are infected with FMD virus. This is done by laboratory tests of samples taken from animals in the ‘proof of freedom’ phase after the outbreak.
If animals are vaccinated against FMD, they will – for a period of time – give a positive test result for FMD.
Under Australia’s current FMD response policy, suppressive vaccination (‘vaccinate to die’) is possible under certain circumstances. Under that policy, all vaccinated animals would be killed during the eradication campaign, that is, there would be no vaccinated animals still alive in the ‘proof of freedom’ phase. Therefore, any animals testing positive in the ‘proof of freedom’ phase would be considered as infected (which means eradication wasn’t as yet successful).
If vaccinated animals have been allowed to live (‘vaccinate to live’; protective vaccination), standard tests cannot tell the difference between a positive result due to vaccination and a positive result due to actual FMD infection. This is where DIVA tests are required, that is, tests that differentiate infected from vaccinated animals.
12. How long would it take for Australia to regain its FMD-free status after an outbreak?
The World Organisation for Animal Health (OIE) recognises Australia as a country ‘free from FMD without vaccination’. According to the OIE standards, the waiting periods – after a successful eradication campaign – required to regain the OIE status of FMD free country are 3 months when stamping out or stamping out with suppressive vaccination (‘vaccinate to die’) has been used, and 6 months when stamping out with protective vaccination (‘vaccinate to live’) has been followed.
For Australia to regain its FMD-free status as quickly as possible (in 3 months rather than 6 months), it would be necessary for a stamping-out policy to apply and – if suppressive vaccination has been used – for all vaccinated animals to be destroyed, in line with the OIE standards. Emergency vaccination of at-risk stock (suppressive vaccination, ‘vaccinate to die’) may result in the need to destroy animals that would otherwise have avoided destruction in a conventional stamping-out approach.
In reality, the OIE does not determine the length of trade exclusion. The point in time following eradication of FMD when export trade resumes will be determined between Australia and its trading partners; regardless what eradication strategy is chosen, exclusion of some commodities from some export markets will most likely last for at least 12 months.
