What happened
Shares of BJ's Wholesale Club (BJ 1.15%) were among the big winners during the first half of the year as the warehouse club chain benefited from consumers stocking up on essentials during the coronavirus pandemic. According to data from S&P Global Market Intelligence, the stock gained 64% over the first six months of the year.
As you can see from the chart below, the stock climbed steadily once the pandemic started and surged on its first-quarter earnings results in May.
So what
The first two months of the year were mostly uneventful for BJ's, but the stock started gaining in March as consumers began stocking up on fears about the coronavirus pandemic. Shares got a boost in early March after the company reported fourth-quarter results that were mostly in line with estimates, and noted that its shoppers had begun stocking up on supplies like cleaning products and canned food. 
Image source: BJ's Wholesale Club.
From that point, the stock climbed steadily through March and April, and it withstood the market crash as investors pinpointed it as a consumer staples play poised to gain on the stocking up behavior while options like restaurants were closed.
In May the stock jumped 21.7% in a single day after its first-quarter report came out. Comparable sales jumped 27% in the quarter, and adjusted earnings per share surged from $0.26 in the quarter per year ago to $0.69, easily beating estimates at $0.34. Those improvements outperformed peers like Walmart and Costco, showing the company got a strong tailwind from the pandemic.
Now what
BJ's stock has continued to gain in July as a resurgence in coronavirus cases makes it likely that the company will see elevated demand. Grocery sales have remained high in May and June, rising about 10% from a year ago.
The pandemic also gives BJ's an opportunity to increase its membership and therefore the efficiency of its warehouses. Membership income growth was much stronger than in the first quarter a year ago, a sign that the crisis is spurring new membership. Growth in its membership base is key as it would provide a long-term benefit to the company, assuming members stay with the club.
