Despite the proliferation of effective vaccines in some parts of the world, coronavirus infections are still rising around the globe. In the U.S., the surging delta variant of the virus is responsible for a whopping 83% of new cases. While it seems that it's mostly unvaccinated people who are getting seriously ill, the unfortunate fact of the matter is that the delta variant is putting the vaccines to the test. 

That's a key consideration for Pfizer (NYSE:PFE), which raked in about $3.5 billion in revenue in the first quarter of 2021 with its two-dose jab. Could the delta variant be a boon for shareholders, or will it threaten the company's bottom line? The answer to this question is far from clear, but at the moment the outlook is more positive than negative.

A nurse vaccinates an older person in a clinic.

Image source: Getty Images.

The potential good news

The most important development in the delta variant's surge thus far is that it looks like Pfizer's vaccine prevents symptomatic infections at a rate of roughly 90%, according to Dr. Anthony Fauci, leader of the National Institute of Allergy and Infectious Diseases (NIAID). Against the risk of severe disease, it appears to be even more effective. So the company will continue to sell the inoculations quite quickly as long as there continues to be global demand from people who are interested in protecting themselves.

Another key factor is that the vaccines made by Pfizer's competitors Johnson & Johnson and AstraZeneca appear to fare significantly worse against the delta variant, though there is no definitive data available yet. Some public health officials are calling for people vaccinated with these less-effective vaccines to get a booster shot from either Pfizer or Moderna to protect them more comprehensively against the delta variant. That could easily lead to millions and millions of additional Pfizer doses sold over the next couple of quarters, which means gains for shareholders

Then there's the prospect of booster shots becoming part of the standard vaccination regimen for all people, which the delta variant's surge has made into a pressing issue. Pfizer is currently seeking authorization in the U.S. to issue booster doses, which might supercharge its revenue even further. But regulators at the Centers for Disease Control (CDC), the U.S. Food and Drug Administration (FDA), and the World Health Organization (WHO) seem to disagree with the company, so widespread rollout of a third dose may be off the table for now. 

Despite a lack of both regulatory support and high-quality data on the merits of a third dose of the vaccine, some countries have decided to move forward anyway. Israel is now offering a third dose of the Pfizer vaccine to immunocompromised people, though it hasn't decided whether to extend that offer to the general public as of yet. 

If Israel decides that it should give out additional doses, it'll mean a small number of additional sales for Pfizer. If larger markets like the U.S. follow suit, shareholders can expect a much larger windfall as soon as the doses can be manufactured and sold off.

World Coronavirus Cases Chart

World Coronavirus Cases data by YCharts

The potential bad news 

There are two problems that the surging delta variant may reveal for Pfizer. 

The first is that breakthrough infections in fully vaccinated people may be far more common, and/or more severe, than the initial data suggested. An analysis published in early July by the Israeli Ministry of Health claims that the Pfizer jab is only 64% effective at preventing symptomatic infection with the delta variant. The analysis also found that the vaccine was still upwards of 90% effective at preventing severe illness, which is an important silver lining. While these results about protection from symptomatic disease are disputed, they pose a discrepancy to Pfizer's effectiveness data.

The picture is still forming, and it's unclear whether a confirmation of lower efficacy against the delta variant would actually result in a lower volume of sales, given that Pfizer's offering would still be among the most effective. But the market might not be pleased if the company's product is shown to perform worse than initially claimed, so there's a small threat to its share price. 

The second issue is that world health authorities may decide to stick to their guns and continue to advise against booster shots for the general public. That probably wouldn't harm Pfizer's stock too much, but it still doesn't look good to get rebuffed repeatedly by the global leaders of the response to the pandemic. In particular, the head of the WHO, Tedros Adhanom Ghebreyesus, has accused Pfizer's push for booster shots to be a matter of "greed," contrasting the radical inequality of vaccine access between the developed world and developing countries. To address this criticism, Pfizer may choose to donate more of its doses to some of the international vaccination efforts.

Overall, these two problems don't pose a major threat to Pfizer. And given the overall effectiveness of its inoculation at preventing severe disease, investors can expect sales volume to keep rising for quite some time, even in the face of the delta variant.

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.