Shares of vaccine maker Moderna hit highs of nearly $500 earlier this year. But they likely aren't getting back to those heights anytime soon. And even at the stock's current price of around $330, many analysts see it as overvalued -- most price targets are no higher than $250.

No doubt, Moderna has been an exceptional investment over the past year, soaring 350% while the S&P 500 has risen by just 29%. But the gravy train for investors may be coming to an end, especially as more vaccines and options for treating COVID-19 become available. Two stocks I'd buy instead of Moderna are AstraZeneca (NASDAQ:AZN) and Merck (NYSE:MRK).

A team of scientists reviewing results in a lab.

Image source: Getty Images.

1. AstraZeneca

AstraZeneca hasn't been focused on making a profit with its COVID-19 vaccine (it actually incurs a loss on it). However, the healthcare company could at some point raise prices on it. The vaccine goes for just a few dollars per dose -- and AstraZeneca has suggested that once the pandemic is over, making a profit on the product would become more of a priority.

Meanwhile, the company is adding to its tools for fighting the illness, including a COVID-19 therapy that it recently submitted to the U.S. Food and Drug Administration (FDA) for Emergency Use Authorization (EAU). It is used in non-hospitalized patients and can reduce the risk of death or a severe case of the illness by 50%.

Although the cocktail may not lead to significant revenue for the business and it may take a while for the company to start making a profit from its vaccine, AstraZeneca is still a safer COVID-related investment than Moderna. The company has many products in its portfolio that contribute to its top line. Oncology, in particular, is a big part of its business and during the first half of 2021 accounted for more than 40% of revenue.

With profits in each of the past five years, a much more diverse business, plus a dividend that yields 2.3% (well above the S&P 500 average of 1.3%), AstraZeneca is a much more stable investment than Moderna over the long haul. 

2. Merck

Drugmaker Merck is another stock I'd buy rather than Moderna. The company is also looking for the FDA to give the green light for a COVID-19 treatment of its own: a pill that reportedly reduces the risk of hospitalization or death by 50%. It is also used in non-hospitalized patients who have mild to moderate cases of the illness.

If it is approved, the company can count on $1.2 billion worth of revenue from the U.S. government for 1.7 million courses of the treatment. Plus, the government has the option to buy 3.5 million more. In addition, several Asian countries are also looking to secure supplies of the drug. Merck will produce 10 million treatment courses this year and will double that production next year.

Merck's pill could be the best alternative next to a vaccine, especially in countries where vaccination rates remain low. Even if Merck doesn't average the hefty $700 per treatment it is getting in the U.S. deal for its COVID-19 pill, the company's top line could easily grow by billions over the next couple of years through this treatment.

Combine that with a business that was already expecting to generate more than $46 billion in revenue this year -- a 12% to 14% improvement over last year -- and earnings per share of at least $4.24, and you've got a pretty safe COVID-19 play with Merck. And despite the excitement surrounding its COVID-19 pill, Merck's shares are up only about 10% in the past month. So there could be a lot more upside for this stock ahead, especially if the FDA grants the pill emergency use authorization.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.