WASHINGTON — New results on a possible COVID-19 vaccine from Oxford University and drugmaker AstraZeneca suggest it is safe and about 70% effective. Some experts say that shows it is likely to win approval.

Partial results from tests of the vaccine in the United Kingdom, Brazil and South Africa were published Tuesday by the medical journal Lancet.

But questions remain about how well it may help protect those over 55. That’s a key concern for a vaccine that health officials hope to rely on around the world because of its low cost, availability and ease of use.

Researchers claim the vaccine protected against disease in 62% of those given two full doses and in 90% of those initially given the half dose. However, independent experts have said the second group was too small — 2,741 people — to judge the possible value of that approach and more testing is needed.