What happened

Diagnostics stocks hit a rough patch this week. Shares of Bionano Genomics (BNGO 2.63%) were down 13.5% for the week as of the market close on Thursday. Invitae (NVTA -6.67%) stock was off by 12% over the last four days, while Opko Health (OPK 5.34%) shares have tumbled by 11.7%.

None of these companies reported news this week that could have given investors reason to sell. Invitae didn't issue any press releases at all. Bionano highlighted presentations about its optical genome mapping technology at the European Cytogenomics Conference. And Opko announced a deal to license its oligonucleotide therapeutics platform to CAMP4 Therapeutics. But while both Bionano and Opko had positive things to say, their news wouldn't have moved the needle much for either stock.

So why did these life sciences stocks fall? Investors could be concerned that with COVID-19 cases in the U.S. rising again, due largely to the rapid spread of the delta variant, Bionano and Invitae could be negatively impacted.

Coronavirus virions with a declining stock chart.

Image source: Getty Images.

However, Opko would likely benefit from higher COVID-19 testing rates if the delta variant continues to pose a problem over the next several months. It's possible that Opko's share price was simply dragged down by the selling pressure on the other diagnostics stocks.

So what

It's too soon to know how the delta variant will impact any of these companies, if much at all. The Centers for Disease Control & Prevention and the Food and Drug Administration issued a joint statement last week that emphasized the efficacy of current vaccines in preventing severe cases of COVID-19 even against the more contagious variant.

Several leading vaccine makers are also moving forward with strategies to combat the delta variant as well as other COVID-19 variants of concern. In the U.S. at least, a repeat of the large-scale lockdowns of 2020 seems unlikely at this point.

Now what

The best thing for investors to do is to evaluate each stock on an individual basis. Diagnostics companies are not exactly alike. 

Bionano should continue to see increased adoption of its Saphyr genomic testing systems. Invitae should also enjoy sustained momentum for its genetic tests, especially if its partnerships with biopharmaceutical companies bear fruit.

Opko is the most dependent of the three stocks on COVID-19 testing. However, the company could also have positive catalysts on the way, including an FDA approval decision in October for somatragon, a long-acting human growth hormone licensed to Pfizer