What happened Shares of e-commerce companies are falling today after Pfizer and BioNTech announced that their coronavirus vaccine candidate has demonstrated 90% effectiveness in preventing participants from contracting COVID-19. Here's how these prominent e-commerce stocks are trading as of 2 p.m. EST: Sea Limited (NYSE: SE): Down 8%. JD.com (NASDAQ: JD): Down 6%. MercadoLibre (NASDAQ: MELI): Down 8%. So what The coronavirus pandemic has driven a broad surge in engagement for e-commerce platforms throughout the year as consumers shifted purchasing patterns away from brick-and-mortar stores toward online alternatives. The prospect of an effective vaccine may reduce or reverse that trend if people are able to go back to safely shopping in physical retail stores. Sea, JD.com, and MercadoLibre operate major e-commerce platforms in Southeast Asia, China, and Latin America, respectively. Image source: Getty Images. Sea has two primary segments: digital entertainment and e-commerce. The digital entertainment segment, which publishes mobile games, has also enjoyed a surge in engagement as people need entertainment while staying home -- quarterly active users jumped 61% last quarter. Gross orders in the e-commerce business soared by 151% and gross merchandise value (GMV) skyrocketed by 110% in the second quarter. While an effective vaccine could hypothetically put a dent in those growth rates, management noted on the last earnings call that certain markets that successfully combated the virus like Taiwan still saw "heightened" growth that was stronger than pre-COVID-19 levels. Sea will report third-quarter results on Nov. 17. JD.com posted a 34% jump in revenue in the second quarter, with annual active customer accounts increasing to 417.4 million. China was able to contain the virus through aggressive lockdown measures earlier this year. The drastic restrictions have already allowed many people to return to relative normalcy in the Middle Kingdom, so the availability of a vaccine may not significantly impact JD.com's current trajectory. "Given the COVID-19 situations, now largely stabilized in China, we kind of go back to our original business plan for the second half," CFO Sandy Xu said in August. MercadoLibre reported third-quarter results last week, and they showed unique active users increasing by a strong 92% to 76.1 million. On a constant currency basis, GMV soared by 117% and total payment volume (TPV) processed through the company's Mercado Pago payment platform jumped by 161%. CFO Pedro Arnt attributed some of MercadoLibre's operating leverage to "the growth in organic demand brought about by the effects of the COVID-19 pandemic on consumer behavior." Now what Pfizer and BioNTech are still conducting clinical trials of the vaccine candidate and currently believe they may be able to produce 50 million doses this year before ramping production to 1.3 billion doses in 2021. The companies have already submitted for Emergency Use Authorization from the U.S. Food and Drug Administration. While progress on a vaccine is great news, it may not be widely available until the third quarter of 2021. 10 stocks we like better than MercadoLibreWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and MercadoLibre wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of October 20, 2020 Evan Niu, CFA has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends JD.com, MercadoLibre, and Sea Limited. The Motley Fool has a disclosure policy.Source