As of Sept. 22, there are now nine experimental coronavirus vaccines worldwide in phase 3 clinical trials, and five vaccines approved for early use despite the lack of scientific data. Although investors' enthusiasm for adequate immunization against SARS-CoV-2 is running high, the reality isn't as rosy. There has never been a vaccine in history developed in the span of only one year, with the fastest vaccine ever developed (for mumps) taking up to four years. The fact that countless experimental coronavirus vaccines have been rushed into development might be a significant oversight that will come back to bite us.

There are many reasons coronavirus vaccine candidates may disappoint -- for example, ongoing mutations rendering vaccine strains archaic, the emergence of severe safety issues, the failure of clinical trials, and experimental vaccines turning out to be only partially effective. In such scenarios, major stock indices such as the S&P 500 would likely witness massive sell-offs -- and panic buying would create demand for these three companies that are doing their part in combating the deadly pandemic. 

Syringe and torn piece of paper with Coronavirus written on it.

Image source: Getty Images.

1. Humana 

Health insurance giant Humana's (NYSE:HUM) business has been soaring this year as patients defer elective procedures due to fear of the coronavirus, a trend likely to continue if COVID-19 vaccines disappoint. In the second quarter of 2020, the company paid out 76.4% of the insurance premiums it collected for patients' medical costs, a significant decrease from the 84.4% it paid out in the first quarter of 2020. That's not all; the company achieved these results despite waiving all cost-sharing for primary care, behavioral health, and telemedicine visits.

Do not be fooled by the seemingly small (8%) decrease in the expense ratio, as it has enormous ramifications simply due to the size of Humana's operations. During Q2 2020, the company's revenue increased to $19 billion compared with $16 billion in Q1 2020, while its earnings per share almost doubled to $13.75.

The company expects to add up to 360,000 total members for its Medicare Advantage program this year and generate up to $17.86 in EPS. For now, the stock trades at a mere 0.75 times price-to-sales and 22 times price-to-earnings, making it an ideal choice for investors looking for value stocks in the healthcare sector. Humana's stock is up more than 42% year over year.

2. Zoom Video Communications

Next up on our list is Zoom Video Communications (NASDAQ:ZM), a tech company at the forefront of digitizing corporate communications to keep employees safe during the COVID-19 pandemic. At 100 times price-to-sales and 600 times price-to-earnings, investors may wonder if there is any rational justification behind buying the company's stock. The answer is in its growth. The company grew its revenue by a stunning 355% in Q2 2021, to $663.5 million year over year.

Throughout the year, the company added 370,200 businesses with over 10 employees each to its video calling platform, an increase of 458% over Q2 2020. At the same time, Zoom's earnings per share increased by almost 32-fold, from $0.02 in Q2 2020 to $0.63 in Q2 2021.

Right now, about 988 businesses have generated more than six figures in revenue on Zoom's platform in the past 12 months. For the full fiscal year 2021, Zoom expects to bring in $2.4 billion in revenue and $2.47 in EPS, a massive increase over the $623 million in revenue and $0.09 in EPS it generated in fiscal 2020. Zoom stock has rallied by more than 467% since last September. 

3. Teladoc Health 

Last but not least, Teladoc Health (NYSE:TDOC) helps patients across the U.S. seek virtual consultation with their physicians, safe from the lethal coronavirus. For the full year, the company expects to increase its revenue to $988 million from $553 million in 2019. Teladoc's sales have been growing by a rate of 67% per year since 2015. 

Teladoc is genuinely a premium telemedicine company, with a patient retention rate higher than 90% and an average of $472 in medical savings per patient per online visit. As a result, the company's U.S. paid membership count and total visits have increased by 92% and 203% year over year, respectively.

In August, Teladoc announced it would be acquiring digital diabetes management company Livongo Health (NASDAQ:LVGO) for as much as $18.5 billion. Livongo is transforming the lives of people with diabetes with its namesake app that can help patients lose weight, improve behavioral health, reduce hypertension, and alleviate symptoms of their conditions. The Livongo app boasts a 94% patient retention rate, as well as an average of $1,908 per participant in annual medical savings. Compared to Q2 2019, membership on Livongo's app increased by 113% annually. 

The two companies can generate significant revenue synergies, as patients with diabetes who seek consultation with Teladoc can receive a referral to sign up for the Livongo app. Likewise, patients who are using the Livongo app to manage their chronic condition can receive a referral to seek treatment with one of Teladoc's physicians. The combined total addressable market for digital health is as much as $120 billion in the U.S. alone.

With Livongo included, Teladoc is trading for about 21 times price-to-sales. Considering its historical growth potential and future opportunities to expand its telehealth expertise internationally, I think Teladoc's growth premium is well justified. The company's stock is up 181% year over year.