The Oxford University coronavirus vaccine produces a "strong" immune response among the elderly, the latest data shows.
Analysis of the Phase II stage of the trial process reportedly found similar responses across all age groups, in findings that have been hailed as a "milestone" in the fight against the pandemic.
It comes as Matt Hancock, the Health Secretary, said he expects a vaccine to be rolled out in the first half of next year, although he said it was possible some people could get access before New Year's Eve.
While they face the highest risk from respiratory infections, elderly people often fail to mount a sufficiently robust response after being vaccinated due to their less active immune systems.
In the field of influenza, this has forced authorities to commission a boosted "adjuvanted" vaccine in recent years designed specifically for pensioners, after the normal jab was found to be ineffective.
Similar fears have dogged the development of a vaccine against Covid-19. However, on Monday both Oxford University and its industry partner AstraZeneca confirmed that the vaccine appears to boost both immunity in the form of antibodies and T-cells.
The candidate drug is currently undergoing a much larger Phase III trial across several countries to try and establish how well it protects against coronavirus in a real-world setting.
As part of a vastly accelerated logistics operation, doses of various candidate vaccines are already being manufactured, even before the results of final studies have been submitted for approval by regulators.
A spokesman for the university said: "These early results covering trial volunteers from the UK in the 56-69 and 70 plus age groups have been submitted to a peer-review journal, and we hope to see their publication in the coming weeks.
"Our ongoing trials will provide further data, but this marks a key milestone and reassures us that the vaccine is safe for use and induces strong immune responses in both parts of the immune system in all adult groups."
AstraZeneca said it was "encouraging to see immunogenicity responses were similar between older and younger adults". The company also said it was pleased to see "lower" levels of side-effects in older adults.
"The results further build the body of evidence for the safety and immunogenicity of AZD1222," a spokesman said.
The Phase II results have not yet been peer reviewed and published, but Professor Andrew Goddard, one of the architects of the vaccine, has discussed them at an academic conference.
Earlier on Monday, Mr Hancock told BBC Radio 4's Today Programme that the vaccine programme was "progressing well".
Asked how soon NHS staff could be injected with a vaccine, he said: "Well, we're not there yet. We're in very close contact with the leading candidates. On my central expectation, I would expect the bulk of the rollout to be in the first half of next year."
When asked if there could be some this year, he said: "Well, I don't rule that out, but that is not my central expectation."
Whilst promising that preparations were under way to roll out a vaccine as quickly as possible, Mr Hancock added: "But, you know, preparing for a rollout and actually having the stuff to roll out are two different things.
"It's obviously something that we want to happen as soon as safely can be done and as fast as safely can be done, but we are not there yet."