There a lot of factors that can affect vaccine efficacy and age is just one of these factors. Others include:
1. Technology platform used
2. Clinical trial design
3. Health status of clinical trial participants (e.g. presence of comorbidities, HIV-exposure etc. )
4. COVID-19 risk exposure
5. Ethnicity
Hence, when clinical trial results are presented, an overall vaccine efficacy is usually indicated then a vaccine efficacy for the different subgroups (e.g. according to age group, ethnicity) may also be indicated. For the vaccines already approved by Philippine FDA for emergency use, the following are the age groups in which they are allowed to be administered:
1. Pfizer-BioNTech - 16 years old and above
2. AstraZeneca - 18 years old and above
3. Sinovac - 18 to 59 years old
4. Gameleya Sputnik V - 18 years old and above
The EUA terms and conditions can be updated as more clinical trial data becomes available from additional age groups or specific population groups.