Investors often consider the healthcare sector a "defensive" one because people get sick in good economic times and bad. Thus, the stocks tend to hold up in times when worries about the economy abound.

That maxim has pretty much been tossed out the window in 2020, along with much of conventional investing wisdom. The healthcare sector has been thrown into turmoil with stay-at-home orders and clinic closures. But biotech stocks have been doing very well, with the iShares NASDAQ Biotechnology ETF (NASDAQ:IBB) up 16% this year.

For investors looking for places to put money in the midst of uncertainty about the direction of the pandemic, stocks of companies in the forefront of important medical advances hold promise for the long term. BioNTech (NASDAQ:BNTX), NeoGenomics (NASDAQ:NEO), and Illumina (NASDAQ:ILMN) are three companies that should come through the pandemic era stronger than ever.

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BioNTech

Stocks that are in the race for a COVID-19 vaccine have seen their shares soar in the past four months, but German biotech BioNTech is still a good buy for the long term. Despite a big partner for the vaccine in Pfizer and an approach based on the same technology as Moderna's, shares haven't risen as far as those of Moderna, and BioNTech's market capitalization is only two-thirds of it.

BioNTech is differentiated from its competitors in that it has four vaccines for the SARS-CoV-2 virus, each with a unique messenger RNA (mRNA) format, in clinical tests designed to quickly narrow down to the most promising candidate. On July 1, the company and Pfizer reported very positive results from a phase 1/2 trial of one of the four candidates, saying that the blood concentration of neutralizing antibodies in the subjects were up to 2.8 times higher than in patients who had recovered from the virus. Still to come soon are results from the three other candidates, and the company expects to start a phase 2b/3 study this month with 30,000 participants.

But the reason to buy BioNTech for the long term isn't for a COVID-19 vaccine, although a win there would be a strong catalyst. The more important driver for the company's business is the company's rich pipeline of next-generation cancer immunotherapies. The company has 10 anti-cancer drugs in 11 clinical trials targeting melanoma and cancers of the breast, ovaries, prostate, pancreas, head and neck, and other solid tumors. BioNTech should produce a steady news flow of results from these trials in the coming months. Success is not a sure thing, but if the news is good, the stock should have a strong tailwind.

NeoGenomics

The pandemic caused hospitals and health centers to postpone elective medical procedures, but what was a little surprising was that even companies that provided services needed to treat severe diseases such as cancer saw a drop in business as the stay-at-home orders went into effect. NeoGenomics is the largest pure-play oncology testing company and saw its clinical test volume drop 20% year over year in the last two weeks of March and between 25% and 30% in April.

NeoGenomics is in a sweet spot in healthcare. Oncology is by far the largest area of investment among drug companies, with 40% of all U.S. clinical development spending going to cancer drug trials, about three times the amount for the therapy area in second place. Driving the industry are new approaches to therapies that target malignancies based on the specific biochemistry and genetics of different cancers. As medicines become more specific, testing becomes an increasingly important part of treatment, and NeoGenomics is growing sales both to clinicians working with cancer patients and to pharmaceutical companies developing new drugs.

NeoGenomics' business should bounce back quickly even if the pandemic resurges, given the urgency of treatment for seriously ill cancer patients. The company didn't furlough employees when the business dipped, so as to be better prepared for the rebound it expects. Revenue growth in the first quarter dipped to 11% after jumping 40% in the fourth quarter, and analysts are actually expecting a 15% decline in revenue when the company reports second-quarter results on July 28. The company continues to expect long-term organic growth in the mid-teens and will probably continue to grow by acquisition as well.

Investors have been buying the stock in recent weeks, after the company launched a new suite of liquid biopsy tests, enabling the detection of cancer biomarkers from blood samples when tissue specimens of solid tumors are hard to obtain. Low expectations in the near term, strong growth prospects for the long term, and the ability to innovate through internal development and partnerships make the stock a buy for patient investors.

Illumina

Illumina dominates the market for gene sequencers, and even though COVID-19 research drove up sales of gene sequencing systems in the first quarter, the company expected sequential declines in revenue in every region in the second quarter. Shutdowns of research institutions and clinics should take a toll on the company's results, which will be reported on Aug. 3.

But longer term, the company is in great shape. The use of genetic information in the diagnosis and treatment of disease is accelerating, while large-scale population studies just getting under way when the pandemic hit will eventually drive big increases in sales of the supplies used in operating Illumina's instruments.

Illumina's business tends to follow the company's cycle of new product introductions. The launch of a major new platform, such as the mid-range sequencers the company announced in January, can cause a temporary slowing of sales as customers stop buying older models, but then it can fuel a strong, multi-year surge in growth as higher sequencing speeds at lower costs draw in new customers. That scenario appears to be playing out this year, with first-quarter revenue up only 2% because of soft system sales, but with almost half of early sales of the new NextSeq 2000 system going to customers who were buying their first Illumina product.

Gene sequencing produces massive amounts of data, so Illumina directs some of its investment to tools that help clinicians and researchers make sense of it all. The company this month launched new software to help detect genetic diseases from genomic information and last month acquired Dutch software company BlueBee, maker of cloud software for interpreting genomic data.

Illumina should emerge from the COVID-19 era stronger than ever, and its latest new products should give the company a boost going into 2021.