Clinical trials for the COVID-19 vaccine being developed by Oxford University are set to resume, after they were halted on September 6th following concerns about a UK participant who developed a possible neurological illness.

The pause in the study had raised public concerns about the Oxford vaccine’s viability, although it was described by a spokesperson of biopharmaceutical firm AstraZeneca as a “routine pause” which was sparked by an “unexplained illness”. The trials will be resumed as soon as possible following a confirmation that it is safe to do so by the UK Medicines and Healthcare products Regulatory Agency (MHRA). 

The nature of the participant’s illness remains unknown, although they are expected to recover, according to Stat News. During the pause, an independent safety review was conducted to determine whether the participant’s illness was linked to the vaccine. The Chief Executive Officer of AstraZeneca, Pascal Soriot, referred to a suspected diagnosis of a condition called transverse myelitis, an inflammatory syndrome affecting the spinal cord that can be caused by viral infections. 

However, Oxford said that further medical information could not be disclosed due to participant confidentiality: “We are committed to the safety of our participants and the highest standards of conduct in our studies and will continue to monitor safety closely.” AstraZeneca has also pledged, along with eight other biopharmaceutical firms, to uphold the highest possible ethical and scientific standards in developing the vaccine.

The development of the Oxford-AstraZeneca vaccine is being closely watched globally. Its position as a strong contender in the expedited race towards a vaccine has lent itself to hopes of its emergence in the market soon. Soriot said on Thursday that the vaccine could still be available by the end of this year. 

Temporary halts in vaccine trials are fairly common. Oxford says it was “expected” that some participants would fall ill in the trialling process, now underway in many parts of the world. So far, some 18,000 people have already received the vaccine. Reports of its successful Phase 1 and 2 testing and its subsequent move to Phase 3 testing in recent weeks heralded a new aim for the expansion of its participant pool to include 30,000 US volunteers. This includes participants with underlying medical conditions. 

Oxford’s Vaccine Research website explains that Phase 3 tests are conducted on thousands of people for “efficacy and safety”. This is to observe whether the experimental vaccine “is safe, leads to a strong immune response, and provides effective protection against the virus”.

The process of human trialling for AZD1222, previously known as ChAdOx1 nCoV-19, began on April 23rd this year. The initial testing of 1,100 volunteers advanced to a study on a much larger scale of more than 10,000 individuals, including those over 55 years of age, across the UK. Though it was more difficult to test the effectiveness of the vaccine due to falling infection rates in May, new confirmed COVID-19 cases have been steadily climbing in the country once again.

The news that the trials are now safe to continue has been welcomed by UK Health Secretary Matt Hancock, who stated: “This pause shows we will always put safety first. We will back our scientists to deliver an effective vaccine as soon as safely possible.”

Both Oxford and AstraZeneca’s statements did not refer to the vaccine tests happening outside the UK. The trialling also included thousands of participants in the US, Brazil, South Africa, and India, all of which were stopped during the temporary pause this week. 

The AZD1222 vaccine candidate itself is created from the ChAdOx1 virus, a weakened adenovirus or form of the common cold that causes infections in chimpanzees. It has been genetically changed so that it is unable to grow in humans, making it safe to use on a very wide range of subjects. Because the vaccine contains the genetic sequence of the coronavirus protein, it is able to produce that same protein when it enters humans to produce an effective immune response against it.

The results of the successful Phase I/II showed increased levels of protective neutralising antibodies and immune T-cells targeting and destroying infected cells, without any serious adverse side-effects. After this, Oxford researchers pressed on with trialing two doses of the vaccine after some volunteers showed stronger responses to it. It remains unclear whether the participant who fell ill received one or two doses, however.

Image credit to CDC/ Unsplash.