Delta, the mutation of the novel coronavirus that originally surfaced in India, is thought to be the most transmissible variant yet as it seems able to, at least partially, evade antibodies from vaccines and infections.More than half of Americans have been fully vaccinated against COVID-19, so states across the nation have lifted restrictions and mask mandates.That is not the case in some parts of the world, however, where the virus is spreading at record pace as governments struggle to contain it.Pandemic Fears Shake MarketsFears that coronavirus is about to make a comeback in a major way have upset markets across the world, according to a new report from HuffPost.In the United States, the S&P 500 fell 1.6 percent. The Dow Jones Industrial Average, meanwhile, slumped 2.1 percent, while the Nasdaq Composite slid 1.1 percent.Companies that would get hurt the most by new restrictions, such as airlines, experienced heaviest losses. United Airlines, for instance, lost 5.5 percent, while cruise operator Carnival fell 5.7 percentage points.U.S. Market Is 'Vulnerable,' Experts SayRandy Frederick, vice president of trading & derivatives at Charles Schwab, explained that the market seems to be very "vulnerable" to bad news."It’s a bit of an overreaction, but when you have a market that’s at record highs, that’s had the kind of run we’ve had, with virtually no pullback, it becomes extremely vulnerable to any sort of bad news.""The valuations, they just got too frothy. There was just so much optimism out there," Chief Equity Strategist at Stifel Barry Bannister stated.World MarketsIn Europe, several markets shrunk around 2.5 percent, signaling that fears regarding the Delta variant of coronavirus are shared across the ocean.Asian shares also fell on Tuesday. According to The Associated Press, South Korea’s Kospi slipped 0.4 percent. Hong Kong’s Hang Seng, meanwhile, lost 0.4 and the Shanghai Composite fell 0.7 percent.Notably, Japan's Nikkei 225 fell 0.6 percent, with just three days to go before the Tokyo Olympics open.The Olympics, some in Japan fear, will accelerate the spread of the Delta variant in the country.Hospitalizations, DeathsAs reported by CNN, data from Johns Hopkins University shows that there has been a surge in COVID-19 cases across the U.S.The average number of new coronavirus cases each day the past week was 32,278, with an average of 258 deaths per day. Additionally, 24,923 Americans are currently hospitalized with COVID-19.The Delta variant and vaccine hesitancy are fueling this surge in cases: John Hopkins University data shows that 97 percent of hospitalizations and 99.5 percent of deaths were among the unvaccinated.