Sustained momentum. That's what growth investors look for. The problem, though, is that past momentum doesn't always translate to continued momentum in the future. 

The good news is that there are plenty of stocks that have strong momentum that should be sustainable. Here are three such stocks that have already doubled this year and still have plenty of room to grow.

Woman holding hand out with images of an ascending stock chart and a dollar sign above her hand

Image source: Getty Images.

1. Novavax

Novavax (NASDAQ:NVAX) hasn't just doubled in 2020. The biotech stock has skyrocketed more than 2,100%. That means Novavax has doubled five times year to date and then added even more gains on top of that.

The biggest catalyst for Novavax has been its coronavirus vaccine candidate NVX-CoV2373. Novavax reported stellar results from an early stage clinical study evaluating the experimental vaccine. It also lined up $1.6 billion in funding from the U.S. government's Operation Warp Speed and supply deals with multiple countries. The biotech has advanced NVX-CoV2373 to a late-stage study in the U.K. and hopes to begin a U.S. pivotal study in the near future.

Novavax also reported overwhelmingly positive results earlier this year from a late-stage study evaluating flu vaccine candidate NanoFlu. The nanoparticle-based flu vaccine went head-to-head against Sanofi's FluZone Quadrivalent and came out on top. Novavax is now moving forward with plans to file for accelerated approval of NanoFlu after it completes a lot-to-lot consistency trial. 

To be sure, Novavax remains a risky stock. There's a chance that NVX-CoV2373 won't perform well in late-stage studies or that NanoFlu won't win regulatory approval. However, my view is that the odds are in the biotech's favor on both fronts. If so, Novavax should keep its sizzling momentum going.

2. Teladoc Health

Shares of Teladoc Health (NYSE:TDOC) have soared more than 150% so far in 2020. This big gain follows a 69% jump for the telehealth stock last year.

Telehealth appears to have hit its stride, thanks in large part to the COVID-19 pandemic. Teladoc's visits have gone through the roof during the coronavirus crisis. 

But is it too late to buy Teladoc? I don't think so. For one thing, recent surveys have found that Americans plan to keep using telehealth services even after the pandemic ends. Teladoc is only scraping the surface right now for an addressable U.S. telehealth market that stands close to $74 billion. It's also a leader in key international markets.

In addition, Teladoc should close its pending acquisition of Livongo Health (NASDAQ:LVGO) within the next few months. Livongo's digital health platform that helps individuals managed chronic conditions should open up new doors for Teladoc. With Livongo's operations under its wing, Teladoc should be well-positioned to reign as the top player in the virtual care market over the long run.

3. The Trade Desk

The Trade Desk (NASDAQ:TTD) delivered the smallest year-to-date gains among these three stocks, but I doubt anyone would complain about an increase of more than 130%. Investors have to be especially happy that this big move follows a 124% vault in 2019.

Two trends serve as tailwinds for The Trade Desk: the move toward digital advertising (especially with streaming TV) and the rising adoption of programmatic advertising driven by software rather than interpersonal negotiations. The Trade Desk ranks as the leader in buy-side programmatic advertising that focuses on the digital ad market.

Granted, the coronavirus outbreaks caused some challenges for the company earlier this year as advertisers curbed their spending during the uncertain times. However, The Trade Desk should actually be helped by this over the long run. Founder and CEO Jeff Green thinks that "the COVID pandemic has permanently accelerated the growth of connective television, changing the TV landscape forever." 

Green firmly believes that The Trade Desk is in the best position to capture market share in connected television. If he's right (and I think that he is), this stock could easily double again within the next year or two.