Many top stocks are heading for annual declines. The bear market has weighed on investor sentiment, and the economic environment, in some cases, has hurt earnings. But among the stocks heading for declines this year, some are showing signs of a rebound.

Right now, I'm thinking of two top healthcare names: Moderna (MRNA 0.89%) and Intuitive Surgical (ISRG -0.55%). Both stocks have posted double-digit increases over the past three months. As you study this new momentum, you may wonder whether you should get in on these players before 2023. Let's find out.

Moderna's post-pandemic market

Moderna has declined about 30% year to date. But the stock has rebounded more than 20% over the past three months. Let's look at what drove the losses and check out the reasons behind the recent increase.

The general market downturn surely hurt Moderna shares. But investors also shied away from the stock over concerns about the post-pandemic coronavirus vaccine market. It's possible Moderna's recent communications about this potential market has assuaged some of investors' fears.

Vaccine sales probably won't top the levels of $18 billion or so that Moderna saw last year and are expected this year. But revenue is likely to remain well within blockbuster territory. Moderna predicts the coronavirus booster market will follow in the footsteps of the flu vaccine market.

Moderna even offered some figures to use as a guideline. The global flu market represents 500 million to 600 million doses annually. Depending on price, this may result in a market of $12 billion to $24 billion for coronavirus boosters.

As of next year, Moderna will transition from filling government contracts to selling vaccine doses directly to pharmaceutical distributors. So the new coronavirus annual booster market should start to take shape. At the same time, Moderna is working on two phase 3 candidates -- vaccines for flu and respiratory syncytial virus -- that may reach commercialization in the coming two to three years.

Plenty of share-price catalysts lie ahead for Moderna. That's why now looks like the right time to get in on the story -- and benefit from this young biotech-company's growth in the years to come. After all, the coronavirus vaccine -- as Moderna's first product -- is likely just the beginning.

Intuitive's unwavering market leadership

Intuitive Surgical has slipped 25% since the beginning of the year. But over the past three months, the stock has rebounded 32%.

The robotic-surgery leader suffered during various moments of the pandemic as hospitals postponed surgeries. Intuitive generates even more revenue from the sales of instruments and accessories used for the surgeries than from sales of the robots. So when surgeries are put on hold, Intuitive misses out on instruments and accessories revenue.

In recent times, though, coronavirus disruptions have eased. And it's possible the worst may be behind this robotic-surgery giant.

Intuitive's most recent earnings report showed double-digit growth in procedures and total revenue. The company also has reached a base of more than 7,300 robotic systems placed in hospitals worldwide. This is a 13% increase over the same period a year ago.

Another positive sign from Intuitive: The company is investing in itself. Intuitive bought back $1 billion of its common stock in the quarter. This shows it's confident about its growth to come.

There's reason for us to be confident, too. Intuitive is the global market leader, by far, with nearly 80% share of the market. Considering the million-dollar price tag on surgical robots, I wouldn't expect hospitals to easily switch to a rival.

Intuitive also continues to gain additional approvals for its surgical systems and connect with surgeons digitally. For instance, the company offers an app that helps surgeons track their work.

Even considering Intuitive's recent gain, it's still trading lower than earlier this year, compared to forward earnings estimates -- 57 times earnings versus more than 72. The recent rebound could lead to more gains in the coming months. Most importantly, it should lead to increases over the long term. Adding Intuitive shares to your portfolio before 2023 sounds like a great way to end the year.