There are many different types of vaccines, but they all work to prevent severe disease. Viral vectored vaccines are one type of vaccine platform that use harmless viruses to deliver genetic information (like a set of instructions) for producing a small part of a pathogen, such as a bacteria, virus, or parasite, into our bodies. This allows our body to produce a harmless part of the pathogen which encourages the immune system to recognise and respond to it, providing protection against future infections.

For more than a decade, the University of Oxford has performed many clinical trials of candidate viral vectored vaccines. These included vaccines against viruses (including coronaviruses), bacteria and parasites, such as malaria. Some of the most promising vaccines used a modified chimpanzee adenovirus, a harmless version of a common cold virus. This led to the development of the ChAdOx platform– two versions of Oxford’s very own viral vectored vaccine platform known as ChAdOx1 and ChAdOx2. ChAdOx vaccines are produced using controlled production methods that enable rapid, large-scale manufacturing.

ChAdOx1 and ChAdOx2 are both non-replicating adenoviral vectors meaning they cannot multiply in the body or cause the disease the vaccine is designed to protect against. The Oxford-AstraZeneca (ChAdOx1) COVID-19 vaccine was approved for emergency use in the UK in December 2020. There are other adenoviral vectored vaccines too, including the Johnson & Johnson Ad26 Ebola vaccine licensed in July 2020.

The Oxford-AstraZeneca COVID-19 vaccine was estimated to have saved six million lives during 2021 alone and over 3 billion doses were used worldwide. In 2024, the Oxford-AstraZeneca COVID-19 vaccine was withdrawn from the vaccine market as a commercial decision. But, the ChAdOx platform does have several advantages that mean it can still play an important role in preparing for future pandemics.

ChAdOx in Outbreak Response

• Temperature Stability: Many vaccines need to be stored at extremely cold temperatures, making it difficult to transport them to remote areas. ChAdOx vaccines are stable at standard fridge temperatures, making them more suitable for regions with limited cold storage. This helps address significant public health needs in areas lacking resources

• Strong Immune Response: ChAdOx vaccines create strong immune responses, which may lead to good protection against the target disease. This is especially important for diseases with high death rates, like Crimean-Congo haemorrhagic fever (CCHF) and Nipah, where even partially effective vaccines may greatly improve survival following infection.

• Established Safety Profile: Years of research have shown that the ChAdOx platform is generally safe. Very rare blood clotting occurred with the COVID-19 vaccine,  but these risks are well understood. The risk of clotting varied by region, with Brazil, the Philippines, South Korea, and Taiwan all reporting around 0.2 cases per 1 million doses - that’s around 1 case in every 5 million doses, but some Nordic countries reported up to 17.6 cases per 1 million. For diseases such as Ebola which can spread easily between people and where up to 9 out of 10 people who are infected can die, the very small risk of blood clots is outweighed by the protection which a vaccine may bring.
  

• Rapid Response: The ChAdOx platform can be employed to produce new vaccines which protect against new or emerging diseases making it ideal for outbreak response. This adaptability may help control disease outbreaks before they escalate.  

ChAdOx vaccines ‘in the pipeline’

ChAdOx-based vaccines against a number of potential outbreak diseases are in development, and work is already underway to test these in clinical trials.  In September 2023, the first volunteers received a vaccine against CCHF, in January 2024, Phase I trials for a vaccine against Nipah virus began, as did trials for a vaccine against Marburg virus in July 2024. A vaccine against Middle Eastern Respiratory Syndrome (MERS) coronavirus has been tested in volunteers in the UK and in Saudi Arabia. Preclinical and Phase I clinical development of vaccines against a number of outbreak pathogens are also ongoing.

The ChAdOx platform plays an important role in developing vaccines for emerging infectious diseases. It facilitates the rapid creation of effective vaccines that can be utilised globally, even in low-resource areas. The Oxford-AstraZeneca COVID-19 vaccine, having saved an estimated 6 million lives in 2021 alone, serves as a powerful reminder of the ChAdOx platform's potential.