July 21, 2020 -- A COVID-19 vaccine developed by University of Oxford and Astra Zeneca, tested on more than 1,000 healthy adults, ages 18-55, triggered antibody and killer T cell responses up to day 56 of an ongoing trial, researchers reported today in The Lancet.

A single dose resulted in a four-fold increase in antibodies in 95% of participants a month after injection and a T-cell response was induced, peaking by day 14, and maintained 2 months later, the researchers report. T cells, a kind of white blood cell, play a central role in the body's immune response.

The vaccine, AZD1222, is made from a weakened version of a common cold virus, the adenovirus, taken from chimpanzees. The adenovirus is genetically altered and can't reproduce itself. It is genetically modified to code for the spike protein of the coronavirus causing COVID-19. When the adenovirus enters the cells of vaccinated people, it also delivers the genetic code for the spike protein, causing the cells to produce it and help teach the immune system to recognize the coronavirus causing COVID-19.

In this phase I/II trial, 543 participants got the new vaccine and 534 received the meningitis vaccine as a comparison. Of those, 113 were asked to take acetaminophen before and for 24 hours after the injections to reduce vaccine-associated reactions, since the vaccine was given in a high dose with hopes of inducing a strong immune response. Ten patients were also given an extra dose of the vaccine 28 days after the first, to see if this was safe and increased antibody and T-cell responses.

Researchers found the vaccine safe and no serious side effects were reported. Fatigue and headache were most common. The acetaminophen did not alter the effectiveness of the vaccine, and it helped reduce side effects such as muscle aches, headache and pain.

The strongest immune response was found in those who got two doses.

In a news release, Sarah Gilbert, a professor at the University of Oxford, said: "There is still much work to be done before we can confirm if our vaccine will help manage the COVID-19 pandemic, but these early results hold promise."

"This is what good would look like, and bodes well for the Phase III trials," said Litjen Tan, PhD, chief strategy officer for the Immunization Action Coalition, who reviewed the results of the Oxford vaccine trials.

Phase II/III trials are under way in the UK, Brazil and South Africa and will start in the U.S., according to Astra Zeneca.

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The Lancet: "Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-blind, randomised controlled trial."
The Lancet news release, "UK's vaccine against SARS-CoV-2 is safe and induces an immune reaction, according to preliminary results."
Astra Zeneca news release, "COVID-19 vaccine AZD1222 showed robust immune responses in all participants in Phase I/II trial."
Litjen (L.J) Tan, MS, PhD, chief strategy officer, Immunization Action Coalition. 

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