Early results from COVID-19 vaccine trials are starting to emerge, and scientists have received the first reports from three independent studies with optimism because protection against the coronavirus is possible.
Although we can be relieved that some vaccines work, we still don’t have the details about the parts of the immune system that made the most difference in these trials. The Pfizer/BioNTech team just completed their trial with 95% efficacy, and the Oxford vaccine team has just published the safety and immune response details on their study (it’s more good news for older people). Whether the Oxford vaccine can prevent COVID-19, however, remains to be determined.
So why is this news important? Vaccines are usually first tested in healthy young volunteers to confirm they are safe and to get the first data on efficacy (whether they show any benefit compared with a placebo). Subsequent clinical trials test the vaccine’s efficacy in different groups of people, such as the very young or the very old, and those with other conditions – diabetes or hypertension, say – that could affect their response to the vaccine.
Oxford vaccine results in young and old
Our immune system wanes as we get older, and it becomes more difficult to mount an effective immune response to common germs that younger people can easily expel. It is well-known that older adults are at a much higher risk of severe COVID-19, so it is critical to develop vaccines that can protect this sector of society. Fortunately, booster vaccinations can be used to bolster immunity in older people.
The Oxford vaccine team separated vaccinated people into groups of 18–55 years (160 participants), 56–69 years (160), and 70 years and older (240). Some received the candidate coronavirus vaccine and some a control meningitis vaccine at one or two doses each, to measure if booster vaccination would help. Their new study, published in The Lancet, investigated whether older adults can develop coronavirus-specific immune responses similar to younger adults.
Not only did the older adults develop similar immune responses to younger people, they also tolerated the vaccine better with fewer reports of side-effects, such as fatigue and muscle ache. Neutralising antibodies that block infection and virus-specific T cells are thought to be important for protective immunity, and older adults in the Oxford trial showed evidence of both. Those who received a booster vaccination had even better responses.
Other coronavirus vaccines in older people
Other studies with vaccine preparations similar to the Oxford group, where the vaccine is delivered by a harmless adenovirus, have reported early results in older people. A single dose adenovirus-based vaccine (CanSino Biological/Beijing Institute of Biotechnology) raised a robust immune response – but less so in those older than 55 years. The two-dose Russian Sputnik V adenovirus vaccine – which also recently reported results in The Lancet – showed consistent responses in under 60s.
Two vaccines using inactivated coronavirus were also able to elicit antibody responses. The Wuhan Institute Biological Products/SinoPharm study showed that volunteers under 59-years-old generated neutralising antibodies, and the Beijing Institute Biological products/SinoPharm study measured robust antibodies but showed lower responses in the over 60s.
A different vaccine approach involves the use of mRNA, messenger molecules that enter our cells and kick off the production of coronavirus proteins to stimulate our immune system. Two mRNA-based vaccines with two-dose protocols were tested under-55s and over-65s with positive results. The Pfizer/BioNTech vaccine was the first concluded trial with 95% final efficacy, and they estimated the efficacy for over 65s at an impressive 94%.
Early results from ongoing trials show that we are able to design vaccines that elicit potent coronavirus responses in people over 60. Vaccine efficacy will vary with different vaccine preparations, and we need to choose carefully which formulations will work best in older people, which doses are most effective and when to administer booster vaccinations to achieve the best results.
It has been less than a year since the new coronavirus jumped to humans, and we are entering the privileged position of being able to choose between different vaccines.
Zania Stamataki is a viral immunologist at the University of Birmingham, UK. She is a member of the British Society for Immunology and she cultures SARS-CoV-2 in category 3 containment labs to characterise immune responses to the virus and to support the development of disinfectants and antivirals. Her team receives funding from UKRI, the Wellcome Trust and the Medical Research Foundation and they collaborate with companies on projects unrelated to vaccines.