The Oxford-AstraZeneca vaccine (henceforth referred to as the AZ vaccine) was approved in the UK on 30 December 2020. A joint project between Oxford University and the British-Swedish pharmaceutical company AstraZeneca, the first dose outside of a trial was given in the UK on 4 January 2021. (1) (2)
This vaccine may prove to be the game changer in the fight against COVID-19. It can be stored in a standard fridge (unlike the Pfizer vaccine which must be stored at -70’C) and thanks to its stability can be transported into care homes, GP practices and vaccination centres as well as hospitals. Unusually for the pharmaceutical industry it is a non-profit vaccine aiming for global supply and equity. AstraZeneca has committed to supplying low-income and middle-income countries with the vaccine. (3)
You can read more about the development of the AZ vaccine and how it works to create immunity here.
How big was the AZ trial?
Trials began in April 2020 and included just under 24,000 participants aged 18 years and over. The trials took place in the UK, Brazil and South Africa. Trials are also ongoing in the US, Kenya, Japan and India.
Half the participants received the vaccine as two separate doses whilst the other half received a placebo injection, also as two separate doses.
The time between receiving two doses varied from 4 to 26 weeks.
Those participants who received the vaccine mounted a high immune response to COVID-19 after their first vaccination and this response increased further after the second dose. Researchers also found that the longer the interval between doses was, the better the immune response with the optimum range falling between four and twelve weeks between doses.
Overall vaccine efficacy was calculated to be 70.4% and it is now recommended that the two doses are given between four and twelve weeks apart.
At 70.4% efficacy the AZ vaccine seems to have a much lower efficacy than the Pfizer vaccine at 91%. However, in the Pfizer trial only participants who developed symptoms of COVID-19 were tested for infection. In the AZ trial all participants were swabbed weekly irrespective of having any symptoms. This means that the AZ trial picked up asymptomatic people with COVID-19 whereas it is not known how many participants in the Pfizer trial went on to catch COVID-19 but were asymptomatic as they were not looked for.
Of particular note was that although some of the AZ vaccine recipients went on to catch COVID-19, none had severe disease or needed to be hospitalised. (Only two people who received the AZ vaccine were hospitalised with COVID-19 and based on the timescale of the start of their symptoms it became clear they were already incubating COVID-19 when vaccinated.)
What is not yet known is whether the vaccine can stop people catching, and therefore spreading, COVID-19 or if it is preventing them from becoming seriously unwell when they do catch COVID-19. If the latter, then an infected vaccinated person could still pass the virus on to an unvaccinated person despite suffering only mild symptoms themselves. (4) (5)
Side effects
All the side effects noted in the trial were described as mild to moderate by the recipients and resolved within a few days of vaccination.
Local reactions
60% of trial participants reported one or more of the following at the injection site:
Pain or tenderness
Redness
Swelling
Itching
Feeling of warmth
Systemic (whole body) reactions
Participants reported side effects very similar to those for the annual flu vaccination and the Pfizer vaccine (click here for more about the Pfizer vaccine)
The most common side effects were:
Headache - 50% of participants
Tiredness - 50% of participants
Muscle Aches - 40% of participants
Raised temperature and/or chills - 30% of participants
Joint Pain - 20% of participants
Nausea - 20% of participants
Older people (aged 65 years and over) reported fewer and milder side effects than younger people. Side effects were also less after the second dose compared to after the first dose across all age groups.
One serious adverse event was reported as possibly linked to the study vaccine. This was a case of transverse myelitis (a rare condition that causes inflammation of the spinal cord) which occurred in a trail participant 14 days after they had received their second dose. The AZ vaccine trial was paused whilst this was investigated, see here for more detail.
Transverse myelitis can be caused by COVID-19 disease itself as well as many other viruses and there have been several documented cases around the world of COVID-19 infection causing it. The participant affected in the trial has made a full recovery and remained in the trial. (6) (7) (8)
Post vaccination
As more and more people are vaccinated it is important to remember that until the pandemic is over we need to keep practicing social distancing, wearing a face mask and washing our hands frequently.
We do not yet know if any of the vaccines will prevent the spread of COVID-19 between people or only lessen the impact of COVID-19 for the individual, not preventing infection but changing it from a potentially serious disease to a mild one. Although a vaccine that reduces COVID-19 to a simple cold-like illness is still hugely preferable to no vaccine, the vaccinated individual with COVID-19 who feels well could still pass it on to the unvaccinated person....and that unvaccinated person could be the one who becomes seriously ill and needs an ITU bed or dies. Only when a substantial proportion of the population have been vaccinated can we realistically begin to talk of returning to “normal”.
The AZ vaccine is likely to be the key player in bringing an end to the pandemic and allowing that normality to return.
