WhatsApp has supported stickers for a long time, but it has always been tedious to add a new pack if your friends didn't happen to send you a sticker from the desired collection via the chat app. The latest version of WhatsApp makes that easier with support for deep links, allowing you to add stickers to WhatsApp by simply tapping an address on your phone. For example, you can add the recently announced "Vaccines for All" pack via this link: https://wa.me/stickerpack/VaccinesForAll.
Deep link support was first spotted by WABetaInfo, and the publication confirms it works for most if not all first-party stickers provided by WhatsApp. Right now, deep links even allow you to download regional sticker packs usually restricted to certain countries, like the Mexican Pictomigos or the Indonesian Hantuku. You can even download stickers meant for businesses.
Regarding the new "Vaccines for All" pack, WhatsApp announced that it created it with the World Health Organization in an effort to help people express their relief, joy, and hope as COVID-19 vaccines are rolling out internationally. The company has also reiterated that it partnered with over 150 local, state, and national governments to create helplines, with over 3 billion messages sent across these worldwide last year.
The new deep links are live in the latest stable version of WhatsApp. If the they don't work for you yet, make sure you're visiting this article from a mobile device or download the latest version of WhatsApp from the Play Store or APK Mirror.