Following the completion of farm activity for Phase 2 of the cattle vaccine field trials in 2023, the government announced a third phase (Phase 3) would be undertaken.

Phase 3 will focus on collecting additional field data from a wider group of cattle to inform options to optimise the performance and reliability of the DIVA (Detect Infected among Vaccinated Animals) test.

The National TB Partnership published its reaction and opinion on the TB Hub following Defra’s announcement.

UK policy

The BCG vaccine is currently not authorised for veterinary use in the UK because it can trigger false-positive results in the official tuberculin skin test, which is the primary method for monitoring bTB in cattle.

The UK follows a ‘test and slaughter’ policy and, if cattle were BCG vaccinated, some may incorrectly test positive. To address this issue, a validated DIVA test is needed to accurately identify infected animals among those that have been vaccinated.

The BCG vaccine provides a broad spectrum of TB protection to cattle, with an expected distribution of around 30% fully protected (no visible lesions or TB culture), 30% partially protected (reduced disease severity), and the remaining cattle being unprotected.

To truly gauge the efficacy of the BCG vaccine in cattle, ongoing monitoring, and evaluation in real-life field conditions, involving extensive sampling, is essential.

It is recognised that collecting performance data from vaccinated cattle exposed to natural transmission in diverse epidemiological situations and in conjunction with other disease control measures is crucial in determining the effectiveness of BCG vaccination in cattle and its potential to reduce disease transmission.

More information can be found on the TBhub.

Progress so far

Progress has been made since a suitable companion test – the Diva skin test – was developed. To date, 300 animals have been vaccinated with BCG in the UK in a global first clinical field trial.

In a joint statement, the Chief Veterinary Officers from England, Scotland and Wales said: “Bovine Tuberculosis represents one of the most difficult animal disease challenges we face today.

“However, the start of these ground-breaking field trials will be welcome news for many farmers who have been greatly impacted by this disease and represents an important step forward in our efforts to deploy a working cattle vaccine by 2025.

“Subject to successful completion of the field trials applications for UK marketing authorisations for cattle BCG and the DST-F (DIVA Skin Test Fusion) will be submitted to the Veterinary Medicines Directorate.”

Vaccination schedule

Once a vaccine is available for use, the vaccination schedule for cattle is likely to vary depending on the specific circumstances and the disease prevalence in the area.

The frequency of vaccination is typically determined based on local disease control strategies, epidemiological factors, and the objectives of the vaccination programme.

Vaccination strategies for bTB may involve single or multiple rounds of vaccination for cattle, and re-vaccination may be considered in areas with persistent bTB challenges.

Our current knowledge, derived from experimental data on the duration of immunity, suggests that an annual vaccination with cattle BCG would be required to sustain maximum protective effect.

WOAH guidance and acceptance

Before starting vaccine field trials in the UK, Defra shared technical information with WOAH (World Organisation for Animal Health) and the EU (European Union) Commission.

Upon successful completion of the field trials, alongside an application for UK marketing authorisations, Defra will also request WOAH validation of cattle BCG and the DIVA test.

Amendments would be required to the WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals and WOAH Terrestrial Animal Health Code. Most countries base their trade conditions on WOAH guidance and acceptance is a crucial step to mitigate any impact to international trade.

According to current guidelines the following items are considered safe commodities and should not require any bovine TB-related conditions, regardless of the health status of the animal populations in the country, zone, or herd of origin:

• Fresh meat and meat products from animals that have undergone both ante- and post-mortem inspections.
• Cured hides, skins, and trophies.
• Gelatine, collagen, tallow, and meat-and-bone meal.

Importing countries require certification for milk and milk products declaring they come from TB-free cattle herds or have undergone pasteurisation or equivalent controls.

The current WOAH standards do not include provisions for vaccinating cattle against TB, as BCG vaccination can disrupt internationally accepted tuberculin-based tests that are crucial for certifying cattle herds as TB-free.

EU trade

Currently, the EU expressly prohibits the use of BCG in live cattle due to its incompatibility with the approved tuberculin-based TB tests. In 2013, the European Food Safety Authority published a scientific opinion on the field trials for bTB vaccination.

Bovine meat exports do not have TB-related restrictions in the EHC (Export Health Certificate). Exporting raw milk requires that the milk comes from TB-free herds.

An amendment to the bovine semen regulations would be necessary for both domestic and EU trade, pending Commission agreement.

Trade requirements are agreed on a bilateral basis between trading partners.

Are products from BCG vaccinated cattle safe to eat?

Meat and related products from BCG vaccinated cattle pose no public or animal health risk when the prescribed withdrawal period has been followed.

Prior to commencing field trials in the UK, the APHA (Animal and Plant Health Agency) submitted a quantitative risk assessment to the VMD (Veterinary Medicines Directorate) to obtain the required Animal Test Certificates.

The Advisory Committee on the Microbiological Safety of Food considered the risk to the consumer from milk, milk products and beef products.

The VMD established a precautionary 90-day meat withdrawal period due to BCG persistence near injection sites and lymph nodes. No milk withdrawal is necessary.

Cattle tested with the DST-F (DIVA Skin Test Fusion) test have no withdrawal requirements for meat, offal, or milk.

BCG vaccine availability for people

The use of cattle BCG vaccine would not reduce the BCG vaccine available for people. 

Its supply for use in cattle will be subject to additional good manufacturing practice manufacturing capacity and a distinct procurement contract.

Approximately six billion doses of the BCG vaccine are administered to humans annually, primarily in childhood immunisation programmes worldwide. Individual countries set their vaccination strategy according to their epidemiological situation.

The World Health Organisation Tuberculosis Report 2023 indicates that global BCG vaccination coverage for infants in 2022 has returned to pre Covid-19 pandemic levels, reaching 87%.