As of my knowledge cutoff in September 2021, the latest regional economic block to be formed is the African Continental Free Trade Area (AfCFTA). The AfCFTA was officially launched on January 1, 2021. It is a trade agreement among 54 African Union member states, aiming to create a single market for goods and services, promote intra-African trade, and enhance economic integration across the African continent.

Out of the options provided, none of them represents the latest regional economic block formed as of my knowledge cutoff date. ASEAN (Association of Southeast Asian Nations) was formed in 1967, COMECON (Council for Mutual Economic Assistance) was dissolved in 1991, APEC (Asia-Pacific Economic Cooperation) was established in 1989, and NAFTA (North American Free Trade Agreement) was replaced by the United States-Mexico-Canada Agreement (USMCA) in 2020.

Please note that the formation of regional economic blocs can change over time, and there may have been new developments or formations since my last update. It`s always a good idea to consult up-to-date sources for the latest information on regional economic blocs.