SCIENTISTS HAVE made headway in Covid-19 vaccine research through a successful trial with pigs.

The Pirbright Institute, working in collaboration with the University of Oxford, have found that two doses of the 'ChAdOx1 nCoV-19' vaccine produces a greater immune response in pigs than one dose, giving greater protection against the virus. Pigs provide a useful model having previously been shown to predict vaccine outcome in humans, particularly in influenza studies.

The results showed that two doses of the vaccine elicits a marked increase in neutralising antibodies, which bind to the virus in a way that blocks infection. It is not yet known what level of immune response will be required to protect humans against SARS-CoV-2. Vaccine efficacy trials are underway in humans, and if the efficacy result is lower than hoped for after a single dose, it is important to know if giving two doses could result in a greater immune response, which could then be more protective.

Director of The Pirbright Institute, Professor Bryan Charleston, said: “These results look encouraging that administering two injections with the same vaccine boosts antibody responses that can neutralise the virus, but it is the response in humans that is important. The pig has proved to be a valuable model for testing human vaccines for other diseases to give an indication of the type of immune response induced and testing different doses. Pigs are more physiologically similar to humans than some other animal models, for example their body weight and metabolic rate, and are more accessible than studies using non-human primates.”

The researchers also compared the effect of a second vaccine dose on T-cell responses. Although their activity was not significantly boosted, the Pirbright study demonstrates that the ChAdOx1 nCoV-19 vaccine also produces robust T-cell responses, which may play an important role in SARS-CoV-2 infection.

Lead author of the study, Professor Simon Graham, said: “While it remains to be determined what immune responses are required to effectively protect people against Covid-19, the demonstration that ChAdOx1 nCoV-19 induces both neutralising antibody and T cell responses is very encouraging. It is likely that a combination of these responses would act in synergy to prevent and control infection, as we and others have recently shown in the context of experimental flu vaccines.”