Studies suggest AstraZeneca COVID-19 vaccine safe, effective

New results on a possible COVID-19 vaccine from Oxford University and AstraZeneca suggest it is safe and about 70% effective, but questions remain about how well it may help protect those over 55 — 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.

Still, experts say the vaccine seems likely to be approved, despite some confusion in the results and lower levels of protection than what some other vaccine candidates have shown.

“What we can see looks reasonable, but it’s a bit more complicated than what we’ve seen so far,” said Dr. Buddy Creech, a Vanderbilt University researcher helping to test two other vaccines. “If this had been the first report out, the field would have still been excited to have a vaccine.”

The medical journal Lancet on Tuesday published partial results from tests of the vaccine in the United Kingdom, Brazil and South Africa — safety results on 23,745 participants and protection levels on 11,636.

They’re hard to interpret because a mistake led some participants to get a half dose followed by a full one rather than two full doses as intended.

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 that more testing is needed.

The half-dose group also didn’t include anyone over 55, and among others in the study, only about 12% were in that age group. Older people also were enrolled later, so there hasn't been enough time to see whether they develop infections at a lower rate than those not given the vaccine.

It’s unclear if the results will be enough to lead...