By Matt Grossman

Pfizer Inc. expects global demand for vaccinations against coronavirus illnesses to last at least several years, sharpening a long-term forecast for its experimental Covid-19 vaccine as the company moves forward with the final-stage of clinical testing.

Mass vaccinations across the globe could be needed into 2022 and booster shots may be needed annually or every few years if the new coronavirus becomes a seasonal or long-term health concern, company executives said Tuesday.

Chief Executive Albert Bourla criticized executive orders signed last week by President Trump aimed at reducing U.S. drug prices, saying such policies risk detracting from the effort to develop Covid-19 medications at a critical time.

"They pose enormous distraction at a time when the industry needs to be completely focused on developing potential Covid vaccines or treatment," Mr. Bourla said on a conference call after Pfizer reported second-quarter financial results.

New-York based Pfizer reported an 11% decline in revenue from a year earlier to $11.8 billion, but the earnings beat analyst forecasts and the company said its manufacturing operations have faced little disruption from Covid-19.

The possibility of long-term demand for a Covid-19 vaccine offers a potential growth opportunity as the company plans to invest more than $1 billion this year developing the vaccine. While the drugmaker already makes top-selling pneumococcal vaccine Prevnar 13, it has been scaling up its manufacturing capabilities around the world in anticipation of a safe and effective vaccine.

"Coronaviruses tend to be skilled at evading sustained immunity," research-and-development chief Dr. Mikael Dolsten said in an interview. Dr. Dolsten said the class of viruses has "adapted to circulate in humans and cross many species, so it would be unlikely that it would just start to disappear."

Angela Hwang, president of Pfizer Biopharmaceuticals Group, told investors on a conference call that the company anticipates standard, or seasonal, vaccinations for a number of years beyond 2022.

Analysts at JPMorgan Chase & Co. estimate Pfizer's vaccine-generating annual sales will reach about $5.5 billion in 2022, assuming an initial price of about $20 a dose in the U.S.

Pfizer on Monday began the last stage, or phase 3, of an experimental Covid-19 vaccine study that seeks to enroll 30,000 people. Pfizer is developing the vaccine, one of the most advanced for the new coronavirus, with BioNTech SE. Another major vaccine developer, Moderna Inc., started its own phase 3 study this week. A vaccine developed by University of Oxford researchers and AstraZeneca PLC that has started late-stage testing overseas is scheduled to begin final, phase 3 studies in the U.S. next month.

Pfizer's study is moving rapidly and is targeting October to file for regulatory approval or emergency-use authorization. The company is aiming to determine the vaccine's efficacy quickly in part by testing in areas of the U.S. where the virus is spreading and by enrolling a diverse population, including high-risk participants.

The vaccine it is giving to trial patients is different from the one for which the companies previously published scientific results. Pfizer said the latest vaccine appears to be more tolerable and could provide better protection from Covid-19.

Mr. Bourla said Tuesday that the company won't charge developed countries outside the U.S. more for the potential Covid-19 vaccine, should it prove to work safely, than what it would charge in the U.S. Developing countries, such as those in Africa, or governments that can't afford the vaccine could pay less, Mr. Bourla said in the interview.

"It's a very different dynamic over there and I will not hold us to the same standard to charge $19 per dose," he said of African countries.

Pricing and cost have emerged as increasingly sensitive issues for vaccine manufacturers and governments that are paying for them. Some companies have said they will charge a price at the cost of producing their shots. Last week, the U.S. agreed to pay Pfizer and partner BioNTech nearly $2 billion to secure 100 million doses, which analysts estimated at about $20 a dose. It also agreed to supply the U.K. with 30 million doses for an unspecified amount.

Pfizer's pricing might change after the pandemic phase, when vaccines would be impacted by typical commercial factors such as competition and volume, Mr. Bourla said on the investor call.

The vaccine the company is testing uses an unproven gene-based technology known as messenger RNA, or mRNA that is involved in making a spike-shaped protein resembling the one on the surface of the coronavirus. The vaccine candidate being used in the final, phase 3 study encodes a full-size spike protein, instead of just a portion of it as was used in the earlier candidate. Pfizer researchers believe this vaccine would offer better protection, particularly for older adults.

Mark Mulligan, director of the Vaccine Center at NYU Langone Health, which began giving doses of Pfizer's vaccine on Tuesday, said he aims to enroll hundreds of subjects in about two months. The company will start by reviewing the more than 1,000 people who expressed interest in Pfizer's early-stage trial, looking "for those with higher-than-average risk," Dr. Mulligan said. "We really have to enroll the right people."

Separately, the company also said it expects to begin testing its experimental antiviral for Covid-19 in humans in September.

Pfizer on Tuesday reported revenue of $11.8 billion, an 11% decline from $13.3 billion a year earlier. Analysts' consensus had forecast sales of $11.58 billion, according to FactSet. The company reported growth in its biopharma division in the latest quarter, but overall sales fell amid increased competition in its generic-drug business.

The pandemic caused quarterly sales to drop about 4%, in part because of disruptions to wellness visits for adults and children. Sales for Pfizer's division of newer, patent-protected medications, which includes breast-cancer treatment Ibrance and blood thinner Eliquis, grew 4% to $9.8 billion, up from $9.43 billion a year earlier.

But the company's overall sales trend was pulled down by falling sales at Upjohn, Pfizer's off-patent drug division. Upjohn's sales declined 32% year over year to about $2 billion, which the company blamed in part on the loss of exclusivity for its pain medication Lyrica. Pfizer agreed last year to combine Upjohn with Mylan NV. The deal, which would create a company called Viatris, is expected to close in the fourth quarter.

Pfizer's quarterly profit was 61 cents a share, or 78 cents a share on an adjusted basis, the company said. Analysts had forecast an adjusted profit of 67 cents a share.

The company also slightly boosted its full-year earnings guidance as it will exist after the Upjohn transaction, raising its projected sales range to $40.8 billion to $42.4 billion. Previously, Pfizer had guided for yearly revenue of $40.7 billion to $42.3 billion. The guidance doesn't account for future Covid-19 vaccine sales.

Write to Matt Grossman at matt.grossman@wsj.com