While the world waits to find out if any of the Covid-19 vaccines in development will be effective, another unknown is how well any successful vaccines will work on the elderly, the group hardest hit by the coronavirus pandemic.
According to the US Centres for Disease Control and Prevention the risk of getting severely ill from Covid-19 increases as people get older. In the United States, eight out of 10 Covid-19-related deaths have been people aged 65 or above, it said.
Less data has been collected on older adults in early trials of vaccines, which typically focus on healthy individuals. There are existing vaccines, like for flu or shingles, that can be less effective as people get older, due to a weakening of the immune system.
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However, some positive data for older adults has been reported for an experimental vaccine by US company Moderna Therapeutics.
Phase one results published on Tuesday in The New England Journal of Medicine show that the mRNA vaccine triggered an immune response in a small group of older people that is comparable to one seen in younger adults. The vaccine is currently in phase three, or final, trials.
“Older adults have been hit hard by Covid-19,” said Nadine Rouphael, interim director of the Hope Clinic of the Emory Vaccine Centre in the US and a principal investigator for the trial.
“It’s critical that they be a part of any vaccination campaign and have confidence that the vaccine is safe and effective,” she said.
Pharmaceutical companies working on Covid-19 vaccines have included older adults in large phase three trials.
“Those kinds of evaluations have to get done if you want an indication for your vaccine in the over 65 age bracket … what’s maybe a little bit unusual is doing everything at the same time,” said John Donnelly, a principal at US-based Vaccinology Consulting.
Testing vaccines “in parallel” in different adult age groups meant regulators could approve Covid-19 vaccine use for older adults at the same time as the typical 18-55 age group, he said.
Companies at the forefront of vaccine testing – America’s Moderna, Pfizer and Johnson and Johnson, and the British-Swedish multinational AstraZeneca – have included a sizeable proportion of older adults in their phase three trials.
Chinese companies also aim to have older adults in their phase three trials, registration data shows. China National Biotec Group and CanSino Biologics have vaccines in trials with adults up to age 85, while Sinovac Biotech has an over 60 group in at least one of its trials.
The immune system ages just like the rest of the body and this can affect vaccine safety or efficiency in older adults, according to immunologist Ashley St. John, an associate professor at Duke-NUS Medical School in Singapore. Part of this is down to the body’s immune memory.
As people age, more of their cells become geared to respond to specific viruses that the body has faced before or to fight chronic infection, she said.
“So you dedicate less energy towards recognising new challenges,” she said, adding that that could affect how well a vaccine could trigger a strong immune response.
But the results from the phase one trial of Moderna’s mRNA vaccine in older people give some hope that this may not be the case.
The study included 40 adults, half aged 56 to 70, and the rest 71 or older. Researchers found both groups had a strong immune response and the vaccine was well tolerated. However, the group size was relatively small and the trials did not evaluate long-term durability of the vaccine, they said.
Participants in both age groups that took a higher dose of the vaccine showed a strong response from helper T cells, another of the body’s defences thought to be a component in fighting the virus, in addition to neutralising antibodies.
“This gives a nice signpost in terms of generating what we anticipate and hope is going to be a protective response,” said Damian Purcell, head of the molecular virology laboratory at the Peter Doherty Institute for Infection and Immunity at the University of Melbourne.
He said phase three data was needed to know whether these immune responses actually blocked the virus or prevented severe disease.
Meanwhile, experts say different vaccines are likely to have varied effects on older adults and some might be more effective than others.
This appeared to be the case in phase two studies for CanSino’s vaccine candidate, published in July, which found increased age and pre-existing immunity to the virus used in the vaccine significantly reduced the immune responses. Researchers at the time said they would continue to evaluate higher doses in an older population in a subsequent trial.
But upping a dose might not be a solution for all vaccines, according to Donnelly, citing potential limitations in doing this with mRNA vaccines due to cost or tolerability.
Balancing these issues meant “it may be a little while before there’s [a vaccine] that is really potent in the elderly. That said, it may still be enough to get by”, he said.
Understanding any differences in vaccine efficacy between adult age groups is also important because it can affect people’s behaviour, according to immunologist Joanna Kirman, an associate professor at New Zealand’s University of Otago.
“Where someone might be very careful in terms of wearing a mask and not going into crowded situations, they can change their behaviour when they are vaccinated and feel invulnerable,” she said.
Meanwhile, having vaccines that covered older adults and, eventually through subsequent studies, children, could be a critical step in stopping the pandemic, Kirman said.
“We are looking at a disease that infects all age groups,” she said. “So when we’re thinking about reaching herd immunity in a community we need a vaccine that will be safe and effective across all age groups.”
More from South China Morning Post:
- Coronavirus: Chinese vaccine ready for use in November, top scientist says
- Coronavirus: Canada confirms planned Chinese vaccine trial has been scrapped after shipments delayed
- Coronavirus: Chinese researchers to test double doses of CanSino’s vaccine candidate
This article Vaccine developers seek to help group hit hardest by Covid-19: the elderly first appeared on South China Morning Post