how did decide which vaccines were very effecrtive effective or somewhat effective
The effectiveness of vaccines is determined through rigorous clinical trials and studies conducted by researchers and experts in the field. These studies typically involve large groups of participants who are vaccinated and then monitored to see how well the vaccine protects them from the disease it is intended to prevent.
In general, the effectiveness of a vaccine is measured by its ability to reduce the incidence of the disease in vaccinated individuals compared to unvaccinated individuals. If a vaccine is found to significantly reduce the risk of contracting the disease, it is considered very effective. If it provides some protection but is not as effective at preventing the disease, it may be classified as somewhat effective.
Additionally, factors such as the duration of protection, the level of immunity provided, and the safety profile of the vaccine are also considered when determining its effectiveness. Ultimately, regulatory agencies such as the FDA and CDC review the data from these studies and make recommendations on the use and effectiveness of vaccines.