Since the level of markets’ information efficiency is key to profiteering by strategic players, Shocks; such as the COVID-19 pandemic, can play a role in the nature of markets’ information efficiency. The martingale difference and conditional heteroscedasticity tests are used to evaluate the Adaptive form of market efficiency for four (4) major stock market indexes in the top four affected economies during the COVID-19 pandemic (USA, Brazil, India, and Russia). Generally, based on the martingale difference spectral test, there is no evidence of a substantial change in the levels of market efficiency for the US and Brazilian stock markets in the short, medium, and long term. However, in the long term, the Indian stock markets became more information inefficient after the coronavirus outbreak while the Russian stock markets become more information efficient. Intuitively, these affect the forecastability and predictability of these markets’ prices and/or returns. Thereby, informing the strategic and trading actions of stock investors (including arbitrageurs) towards profit optimization, portfolio asset selection, portfolio asset adjustment, etc. Similar policy implications are further discussed.

由于市场的信息效率水平是战略参与者牟取暴利的关键，因此，Shocks; 例如COVID-19大流行，可能会在市场信息效率的本质中发挥作用。CO差和条件异方差检验用于评估COVID-19大流行期间（美国，巴西，印度和俄罗斯）受影响最大的四个经济体中四（4）个主要股市指数的市场效率的自适应形式。通常，基于the差谱测试，没有证据表明短期，中期和长期美国和巴西股票市场的市场效率水平有实质性变化。但是，从长远来看，冠状病毒爆发后，印度股票市场的信息效率降低，而俄罗斯股票市场的信息效率提高。直观地讲，这些因素会影响这些市场价格和/或收益的可预测性和可预测性。从而，将股票投资者（包括套利者）的战略和交易行为告知利润优化，投资组合资产选择，投资组合资产调整等。进一步讨论了类似的政策含义。