Right now, there are 50 coronavirus vaccine candidates in clinical trials worldwide, and there is a good chance that at least one of them can earn approval from the U.S. Food and Drug Administration (FDA). If that happens, any business that had its revenues hit hard by COVID-19 could witness a full-on recovery and major gains in its stock price.

This could happen sooner than we think; Pfizer (PFE -0.21%) and BioNTech (BNTX -0.32%) are set to publish results on large-scale testing of their experimental coronavirus vaccine next month, and 10 other candidates are in phase 3 clinical trials. Consumer confidence declined to levels not seen since the 2008 financial crisis at the start of the pandemic, and a vaccine approval would be a huge catalyst for global economic revitalization. Here are the three best stocks to buy in the event that vaccine trial results are positive and allow consumers to turn their attention back to businesses.

Vials labeled "COVID-19 vaccine" on top of $100 bills.

Image source: Getty Images.

1. Expedia 

During the second quarter of last year, travel company Expedia (EXPE 0.74%) realized $28.3 billion in total bookings for air travel, lodging, car rentals, and vacation packages on its platform. In Q2 2020, the company had just $2.71 billion in orders, due to new stay-at-home orders and travel mandates. However, there is a huge opportunity for the company's stock to make a sharp rebound, as long as the worst is behind us. At one point during the year, Expedia stock fell to almost $40, down from about $110 on Jan. 1.  

In the event that a coronavirus vaccine makes it past large-scale clinical trials, immunization programs would undoubtedly help restore consumer confidence in the global travel industry. Last year, Expedia generated $12 billion in revenue and achieved $3.77 in earnings per share (EPS). The company's market cap is now down to $12.57 billion, barely above 2019 sales. 

Fortunately, Expedia does not have to deal with any liquidity problems. Its $5.5 billion cash balance is enough to cushion its $6.9 billion in long-term debt. Despite its revenue and early stock price woes, the company's stock has managed to rally by more than 92% over the past six months.

2. Boeing

Boeing (BA -1.00%), one of the world's largest aircraft manufacturers and defense contractors, is not having a good year, because the pandemic has significantly disrupted commercial aircraft demand. As of July, daily global passenger aircraft volume was still down to about 50,000 from 100,000 in the year prior. Simultaneously, the continued grounding of its 737 MAX jets did not help Boeing's bottom line. In the second quarter of 2020, Boeing's revenue decreased to $11.8 billion from $15.8 billion in Q2 2019.

Luckily, there is a light at the end of the tunnel for Boeing. The company expects its massive backlog of 4,500 commercial plane orders to generate $326 billion in future revenue. Boeing also has $64 billion worth of military orders and $18 billion in orders for aircraft services worldwide to survive these challenging times.

If a coronavirus vaccine is fully approved, Boeing would be the first to benefit from the subsequent rebound in air travel. The stock currently trades for as little as 1.3 times forward price to sales (P/S). Meanwhile, Boeing's $32.4 billion in cash and investments is enough to start tackling its $59.5 billion in long-term debt. Since its low point in March, Boeing stock is now up 65% over the past six months.

EXPE Chart

EXPE data by YCharts

3. SmileDirectClub

Since its inception, SmileDirectClub's (SDC) 3D clear teeth aligners have been in high demand. Over 1 million people in the U.S. use the company's aligners, with an estimated 97% satisfaction rate. Compared to traditional braces, SmileDirectClub's aligners are more convenient and require four to six months per treatment course on average.

Even though SmileDirectClub has an online dental channel, it also relies on patients receiving an in-person dental scan at the company's retail locations. That business model was hit hard by COVID-19 lockdown measures, which forced nearly all of its 418 SmileShops in the U.S. to close. In Q2 2020, SmileDirectClub's revenue decreased by 45% year over year to $195.8 million. SmileDirectClub stock fell below $4 in March, and now sits at $10.67.

Although many of these shops have reopened, patients are still deferring elective procedures due to fear of the coronavirus. Should a coronavirus vaccine be distributed, these fears are likely to dissipate. That would be great news for SmileDirectClub, which would hope that it could continue the 53% year-over-year revenue growth that it enjoyed before the pandemic hit.

For now, the company's financial health is also decent, with about $389 million worth of cash to offset $420.3 million in debt. If healthcare investors are looking to grab a growth stock at a rock-bottom price, consider that SmileDirectClub only has a $6.3 billion market cap. From March to September, the company's stock is up over 170%.