CLEAN : S.Africa to begin vaccination rollout with Johnson & Johnson's jab: health minister

The Department of Health is continuing with phase one vaccination using the Johnson & Johnson vaccine, proven effective against the 5:01 Y V2 variant. Approval processes are in place for its use in South Africa. Pfizer vaccines have been secured for early rollout. Scientists are evaluating other candidates, including Sputnik V, and deliberating on AstraZeneca's use. Unused AstraZeneca vaccines will be exchanged before expiry to prevent waste.

What ongoing evaluations are scientists in South Africa conducting regarding vaccines?

What is the purpose of exchanging unused vaccines before they expire?