Researchers at the Pirbright Institute, in collaboration with researchers at the University of Oxford, have successfully shown that two doses of the ChAdOx1 nCoV-19 (AZD1222) vaccine produce a greater antibody response than a single dose in pigs.
SARS-CoV-2, the virus that causes COVID-19 in humans, has caused a global pandemic that continues to impact the world. Researchers are furiously working to find a vaccine to combat this global emergency.
Pirbright reports in a press release that the ChAdOx1 nCoV-19 vaccine developed by researchers at the University of Oxford is now being tested in humans. They are hopeful an effective vaccine could be produced as early as later this year.
This vaccine candidate was developed by a team of scientists at the Jenner Institute using a chimpanzee adenovirus vaccine vector that contains the spike protein from SARS-CoV-2, the release said.
The studies carried out by Pirbright researchers were designed to establish whether two doses of the new vaccine in pigs (prime and boost), might elicit an even greater immune response, and maybe a more effective approach, to developing a protective response, the release said.
Pigs are a useful model because they have been known to predict vaccine outcome in humans. They are also more physiologically similar to humans than other animal models, especially in body weight and metabolic rate, and are more accessible than studies using non-human primates.
“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,” said Bryan Charleston, director of The Pirbright Institute. More research in humans is still needed, he added.
Researchers saw a marked increase in neutralizing antibodies that bind to the virus in a way that blocks infection, Pirbright noted. However, it is still unknown 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,” Pirbright said.
The researchers also compared the effect of a second vaccine dose on T-cell responses. Although their activity was not significantly boosted, the study demonstrates the vaccine candidate produces robust T-cell responses.
“Comparing the results of these studies with responses seen in humans will demonstrate whether pigs are valuable models that can be used for further evaluation of the immune responses generated by ChAdOx1 nCoV-19 and other COVID-19 vaccine candidates,” Pirbright said in the release.
The results of this research are published in bioRxiv and as such have not yet been peer reviewed.
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