For the first time since 1996, there are currently outbreaks of Newcastle disease (ND, or atypical avian influenza) in Germany. ND is a Category A notifiable¹¹ animal disease (Regulation (EU) 2018/1882), which is listed in accordance with Article 5(1) of Regulation (EU) 2016/429 (Animal Health Law⁸) and constitutes an animal disease under Article 9(1)(a) of the same Regulation2.
In Germany, vaccination has been compulsory for chicken or turkey flocks since the 1990s, pursuant to Section 7(1) of the Ordinance on Protection against Avian Influenza and Newcastle Disease of 20 December 2005⁹. This applies to all commercial and private livestock holdings, regardless of the number of ^animals1,2. 
To avoid the risk of pathogen introduction, the highest possible level of biosecurity should be maintained in every flock5^,7.

Following an incubation period of 2 to 5 days, conjunctivitis, a runny nose, nasal discharge, respiratory distress, diarrhoea and, in later stages, paralysis and other central nervous system disorders, including head tilt, may occur. In laying hens, there is often a sudden drop in egg production and discolouration of the eggshell. Infected animals may die after 3 to 7 days, with up to 100 per cent of the flock being affected, particularly in younger animals. At the same time, milder disease courses with non-specific clinical signs are also being observed in the current outbreak. This applies in particular to vaccinated flocks. Waterfowl generally show few clinical signs following infection. Therefore, in cases of unexplained disease progression and deaths, testing should be carried out not only for avian influenza but also for ND4.

Vaccination can be carried out using ‘traditional’ live, vector (live) and/or inactivated vaccines. Live vaccines are administered via drinking water, as a coarse spray, or, in the case of individual animals, as eye drops. Vector vaccines can be administered by injection on the first day of life, or into the hatching egg (in ovo). The limited duration of immunity for live vaccines is approximately 6 to 8 weeks; in this case, a booster vaccination must be administered in accordance with the manufacturer’s instructions. Injectable inactivated vaccines (‘needle vaccination’) are administered as a booster vaccination following initial immunisation with a live vaccine and provide protection for approximately one laying cycle. 
In hobby flocks, an annual booster with an inactivated vaccine should be carried out following the primary immunisation. In larger flocks, booster vaccinations are usually carried out using live vaccines via the drinking water or by spray. As none of the vaccination techniques can ever guarantee that 100% of the animals in a flock will be reached or develop immunity, it is recommended in the current situation, in consultation with the flock’s attending veterinarian, to carry out more frequent booster vaccinations where necessary.

Since April 2020, live vaccines against Newcastle disease that can be administered via drinking water may also be dispensed by the herd veterinarian to non-commercial and non-professional keepers (hobby keepers) (§95a (4) TAMG)^1,3,10. In accordance with Section 95a(1) of the Veterinary Medicines Act (TAMG)¹⁰, inactivated vaccines may also be used by commercial and professional keepers if they are dispensed by the herd veterinarian10.
Further information on the correct administration of vaccinations can be found in the article by the Netzwerk Fokus Tierwohl (Animal Welfare Network) “Ensuring animal health through vaccination – how do I do it properly?⁶”, using broiler chickens as an example. It is important to note that the live vaccine must be consumed by the animals within two hours of mixing and that no partial quantities may be taken from an opened vaccine vial or bottle. The drinking water used must not be too warm, and the drinking lines/troughs must be free of residues (e.g. acids or disinfectants). To ensure the animals consume the vaccine within 2 hours of mixing, it is best to vaccinate early in the morning. On veterinary advice, the animals’ access to water may also be temporarily restricted beforehand. To estimate the amount consumed within 2 hours as accurately as possible, water consumption can be measured at the same time of day the previous day. In addition to the vaccine itself, stabilisers, available from vaccine manufacturers, can be added to the drinking water. These substances are dissolved before the vaccine and are intended to help ensure that the vaccine is not damaged by certain residues in the water during administration. Furthermore, the stabilisers often contain dyes. The dye can be used to check whether the drinking lines are completely filled with vaccine solution at the start of vaccination. A blue discolouration of the tongue 2 hours after the start of vaccination makes it easy to verify that sufficient vaccine has been taken up6. 

As with a COVID-19 vaccine for humans, protection cannot be guaranteed 100% with an ND vaccine either. The aim is to build up the highest possible level of herd immunity. Repeated vaccinations can reduce the proportion of ‘non-responders’, i.e. animals that show no immune response despite correct vaccination6. Vaccinated animals shed less virus over a shorter period. If clinical signs do appear, they are less pronounced. Young animals during the rearing phase are not yet protected, or are insufficiently protected, which is why these herds are particularly at risk.

In view of the current disease situation, the Friedrich Loeffler Institute (FLI) recommends a booster vaccination for herds. If there are any uncertainties regarding vaccination, it is advisable to consult the herd’s attending veterinarian or the relevant State Office for Consumer Protection and Food Safety.

If, despite all precautionary measures, there is a suspicion of an ND outbreak, the veterinarian responsible for the flock, or the veterinary office of the relevant district or independent city, must be notified. In accordance with the “Ordinance on Protection against Avian Influenza¹²”, the livestock owner is obliged to investigate any losses of 2% or more within 24 hours, or a drop in egg production of 5% within 24 hours. There are numerous other causes that can lead to similar symptoms and which are generally treatable. Early diagnosis is therefore always advisable in order to be able to take appropriate measures in good time. Should an avian influenza or ND investigation be necessary, the veterinary office, or veterinarians commissioned by it, will take official samples from the flock, which will be examined at the relevant regional laboratory. Once a suspected case has been confirmed by the regional laboratory or the FLI, susceptible animals in the flock must be culled and disposed of in accordance with national and EU legislation. This also applies to flocks where animals have become infected despite vaccination. Provided the animal keeper has complied with animal health regulations, they are entitled to reimbursement of the costs of culling and disposal, as well as compensation for the market value of the animals. In addition, the prescribed protection and surveillance zones are established and outbreak investigations are carried ^out by the authorities4.