Question

as covid - 19 spread throughout the world in late 2019 and 2020, scientists raced to develop an effective vaccine to stop the spread of the lethal virus. by june 2020, there were over 120 vaccine candidates in various stages of progress. given the phases of vaccine approval shown in the image below, rank the following vaccine candidates studied in june 2020 from most advanced in development to least advanced in development.

a new vaccine is extensively tested.
the first trials are performed on animals or cell lines (collections of identical cells).
three phases of clinical trials are conducted on adult human volunteers.
if the vaccine proves to be safe and effective, the fda approves it for commercial sale.

takis biotech: developing five dna - based vaccine candidates based on the spike protein of covid - 19; each contains pcr (polymerase chain reaction) - produced pieces of linear dna instead of traditional circular plasmids; vaccines could be quickly produced

moderna: reported successful animal antibody response and positive response in the initial group of 45 human volunteers; testing an additional 600 human volunteers and recruiting the next group of 30,000 human volunteers

oxford university/astrazeneca: reported successful antibody response in monkeys; tested 1,100 adult human volunteers initially; began testing on two groups of 10,000 human volunteers simultaneously; reported data for the 10,000 - person group limited to subjects 18 years of age and older

medicago: rapidly developing plant - based vaccine; previously successful with flu vaccine; reported positive antibody results in mice; recruiting human volunteers

Explanation:

Vaccine development phases progress from animal - cell tests to human clinical trials and then approval. More human trials mean more advancement.

Answer:

1. A new vaccine is extensively tested (most advanced, after clinical trials).
2. Three phases of clinical trials are conducted on adult human volunteers.
3. The first trials are performed on animals or cell lines.
4. If the vaccine proves to be safe and effective, the FDA approves it for commercial sale (least advanced as it's the final step after all testing).