Two COVID-19 vaccines have been shown to prompt an immune response, which may prevent COVID-19, in humans.
The results are from the University of Oxford’s ChAdOx1 vaccine candidate, and China’s Ad5-vectored vaccine candidate. While both vaccines have produced a good immune response, more testing is needed to confirm whether they can actually stop the development of COVID-19.
The SMC asked experts to comment on the papers.
Associate Professor Helen Petousis-Harris, Vaccinologist, University of Auckland, comments:
“In order to be effective, vaccines need to elicit the right type of immune response against the right targets. In the case of COVID-19, most vaccines are targeting what is called the spike protein, which the virus uses to gain entry into our cells and infect them. Last week early results from the Moderna mRNA vaccine were published, indicating that a broad immune response against the virus’s spike protein was triggered. This week data from both the Oxford viral vector vaccine and a viral vector vaccine from CanSino in China also indicate good immune responses are generated.
“While the Oxford and CanSino vaccines are both viral vector vaccines, the viruses used to carry the SARS-COVID-19 spike protein gene are different. While the Oxford vaccine uses a virus that does not normally infect humans, the Chinese version uses a virus that does commonly infect humans. There is a possibility that vaccines made with the human virus may be less effective because some people may already be immune to them.
“There are no serious safety concerns noted with these vaccines at this stage. It should be expected that some people will experience symptoms consistent with making a nice immune response. Other than pain and redness at the site of infection, this includes headache and fever – duration is short. Providing these events are not too severe it can be seen as a sign of the body making immunity.
“There are recent reports suggesting protection from a COVID-19 vaccine may be brief. These are largely based on recovered cases where antibodies are observed to wane. This does not mean that these people are not still protected and it does not mean that vaccine protection might be short-lived. There are a number of mechanisms involved in protection that we are not measuring and, with respect to COVID-19, do not yet fully understand.
“Ultimately we will only know the effectiveness of these vaccines once they have been through the next phases of study and the rates of COVID-19 in people who received the vaccine can be compared with the rates in people who received a placebo (no vaccine). The length of time people are protected for will not be known for much longer. So far, these vaccines appear to be pushing the right buttons and we can be cautiously optimistic.”
Conflict of interest statement: Helen has no COVID-19 related conflicts of interest.
Associate Professor Siouxsie Wiles, microbiologist at the University of Auckland, comments:
“The two new Lancet papers describe the results of early human trials of two of the 150 candidate COVID-19 vaccines currently under development – the Oxford/AstraZeneca vaccine candidate (ChAdOx1) and the Beijing Institute of Biotechnology/CanSino Biologics Ad5-vectored candidate. Both these vaccines are based on weakened forms of cold viruses (adenoviruses) that aren’t able to replicate in human cells and which have been engineered to express the spike protein from the COVID-19 virus. The Oxford/AstraZeneca vaccine uses an adenovirus originally from chimps and the Beijing Institute/CanSino vaccine uses a human adenovirus.
“The trials show that both the Oxford/AstraZeneca vaccine and the Beijing Institute/CanSino vaccine are safe over the short term and that the majority of healthy people vaccinated mount an immune response. This is very promising news but doesn’t mean we should be expecting a vaccine to be widely available anytime soon. The next step is to find out whether either of the candidates protects people against COVID-19. Studies to find this out for the Oxford/AstraZeneca vaccine are now underway in Brazil, the UK, and South Africa. These are designed to take a year but I imagine if they look promising we’ll hear much sooner than that.”
No conflict of interest.