"The challenges in the development of a COVD-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from Covid-19", Chen explained.
Given that it takes several years to develop an effective vaccine for a viral disease, world leading pharmaceutical companies and universities are in the race to develop a COVID-19 vaccine because the pandemic has infected almost five million people and killed almost 600,000 within five months.
Speaking to the Sunday Telegraph, Professor Hill explained that the Oxford University Research group is facing "a race against the virus disappearing, and against time". The Oxford vaccine also uses a common cold virus as its primary delivery system, albeit a different adenovirus to the Ad5-nCoV vaccine being developed in China.
Since its inception, Bharat Biotech has been very successful in developing some of the effective vaccines which has a long-lasting impact on the health of millions across the world. However, the researchers mentioned in the study that they don't know for sure how much the vaccine would be protective against COVID-19 since they don't know much about the effectiveness of antibodies and T-cell response against the disease.
Unproven in humans, mRNA vaccines work by using the body's own cellular machinery to code for proteins found on the surface of the coronavirus - in most cases the "Spike" protein it uses to latch on to cells and infect them. Serum is carrying out phase 3 trials of recombinant BCG vaccine.
The phase 1 trial involved the substance being administered to 108 healthy volunteers in Hubei province, the original epicenter of the outbreak.
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Adrian Hill, director of Oxford's Jenner Institute, which has teamed up with drugmaker AstraZeneca Plc to develop the vaccine, said that an upcoming trial, involving 10,000 volunteers, threatened to return "no result" due to low transmission of COVID-19 in the community.
Now more than 10,200 people - including over 70s and five to 12-year-olds - will be enrolled in the study, to see the effects on their immune system. We said earlier in the year that there was an 80% chance of developing an effective vaccine by September.
Two weeks after vaccination, participants in all three groups showed some level of an immune response to the virus.
Based on the results, the researchers said the vaccine was well tolerated by the volunteers at all doses with no serious adverse events reported within 28 days of vaccination.
Candidates that demonstrate safety in small early studies will be tested in huge trials of 20,000 to 30,000 subjects for each vaccine, slated to start in July.
Trials should assess whether vaccines cause an increase in the disease, a potentially unsafe side effect in which the vaccine worsens the disease in some people rather than preventing it. Trials will need to assess if the vaccines cause disease enhancement - a potentially unsafe side effect in which the vaccine makes the disease worse in some individuals instead of preventing it. Disease enhancement has been seen in animal studies of vaccines developed to fight a close cousin of the virus that causes COVID-19.