Cleaning has begun at the Suffolk farm where 159,000 turkeys were culled after a bird flu outbreak.
All the empty sheds that housed the birds at the Bernard Matthews plant in Holton will be disinfected.
The Health Protection Agency (HPA) said more than 320 farm workers had taken the antiviral drug Tamiflu and so far no-one had reported being ill.
Strict controls are in place around the site near Lowestoft, but officials say the risk to humans is "negligible".
The HPA said workers who had taken the antiviral drug included the small group who may have handled more than 2,000 birds who died from the virus.
Following the outbreak, Japan, South Africa, South Korea and Hong Kong have banned imports of UK poultry.
Russia is still allowing the importation of cooked meats.
Britain is Europe's second-largest poultry producer after France, with annual exports totalling £300m.
But Bernard Matthews commercial director Bart Dalla Mura insisted there would be no adverse effect on the poultry industry.
He said consumers were "savvy enough" to see that the disease was being dealt with.
Chief veterinary officers from the 27 EU member states discussed the outbreak at a meeting on Tuesday.
In a statement afterwards, the European Commission said the UK was doing everything correctly to deal with the outbreak and advised against a widespread vaccination of birds.
An international conference on vaccination will take place in Verona in March.
A 3km (1.9 miles) protection zone and a 10km (6.2 miles) surveillance zone are in place around the farm.
Poultry owners in a wider restricted zone, covering 2,090 sq km (807 sq miles) around Holton, have been told to keep their flocks isolated from wild birds.
After the culling operation, the carcasses of the birds were transported to a plant in Cheddleton, Staffordshire, for incineration.
BBC correspondent Richard Bilton said the cleaning and disinfection of the area could last for weeks.
Experts are trying to find the source of the outbreak of the disease which was identified as the potentially deadly Asian strain of the H5N1 bird flu virus.
Tests could take weeks and it is possible the exact cause will never be known.
The government says it is preparing for the "very remote possibility" the disease could mutate into a form that could spread from human to human, causing a flu pandemic.
The Department of Health has taken the advice of scientists to stockpile enough Tamiflu antivirals to cover a quarter of the population.
The H5N1 virus, which causes bird flu, does not pose a large-scale threat to humans as it cannot pass easily from one person to another.
But experts fear the virus could mutate and trigger a flu pandemic, potentially putting millions of human lives at risk.
Scene of outbreak
All poultry to be culled
Visitors disinfected and restricted access
3km Protection Zone
Poultry kept indoors and tested
10km Surveillance Zone
No movement of poultry to or from area except for slaughter
Trains carrying live poultry are prevented from stopping in the protection zone
Bird fairs and markets banned
Increased surveillance of wetland areas
Domestic birds not to share water used by wild birds
Footpath restrictions likely only on free-range farms
People in towns not affected unless they keep poultry.
Isolation of poultry from wild birds
Poultry movements to be licensed