The first few months of 2020 were terrible for Boeing (NYSE:BA) shareholders. Boeing stock had already struggled in 2019 because of the 737 MAX grounding. The COVID-19 pandemic made the aerospace giant's troubles much worse by torpedoing aircraft demand.

However, Boeing shares have shown signs of life recently, thanks to positive news about coronavirus vaccine development. Global vaccine distribution over the next year could potentially bring the COVID-19 pandemic under control, enabling an air travel recovery. Let's see if the recent vaccine progress could represent a game changer that allows Boeing stock to return to its 2019 all-time high.

BA Chart

Boeing stock performance, data by YCharts.

Vaccines are coming

The world has gotten a lot of good news about COVID-19 vaccines this month. Studies found that vaccine candidates developed by Moderna and a Pfizer-BioNTech partnership are each approximately 95% effective at preventing COVID-19. More recently, Oxford and AstraZeneca announced that their vaccine candidate is up to 90% effective when administered using a smaller initial dose.

Vaccine developers have already laid the groundwork for rapidly scaling up production. Moderna plans to make 500 million to 1 billion doses next year. The other vaccines could be produced at even higher rates, including up to 3 billion doses of the Oxford-AstraZeneca option. And there are plenty of other vaccine candidates in development that could potentially be ready to be distributed in volume next year.

The global rollout of effective vaccines should make it safe to travel again by the end of 2021 -- and possibly even by the summer, depending on the pace of vaccination campaigns. That would pave the way for a recovery in air travel demand, which ultimately underpins demand for Boeing's commercial jets.

Recovery won't be immediate

Vaccine availability will be a game changer for air travel demand. However, it won't necessarily be a game changer for Boeing stock.

The International Air Transport Association doesn't expect global air travel demand to return to 2019 levels until 2024. Economic damage from the pandemic could weigh on demand long after the pandemic ends. For example, people who have lost their jobs may not be able to afford to travel for a while. Perhaps more significantly, belt-tightening by struggling companies could limit business travel demand for many years, particularly now that people are becoming accustomed to using videoconference tools like Zoom.

Faster-than-expected vaccine deployment might speed up the recovery timeline, allowing global airline passenger traffic to reach 2019 levels by 2023 instead of 2024. However, that would still imply four "lost years" of zero growth.

Growth vs. replacement

Until air travel demand actually surpasses 2019 levels, airlines won't need to expand their fleets. They will only need to buy enough aircraft to meet their replacement needs. That's a problem for Boeing, because in recent years, the vast majority of aircraft deliveries were used for growth rather than replacement.

This shouldn't be surprising. After all, Boeing and Airbus delivered a combined 1,606 commercial jets in 2018 (the year deliveries peaked): more than double the number of mainline jets built annually in the 1990s and early 2000s. Without growth-related demand, aircraft manufacturers will have to keep production far below pre-pandemic levels over the next few years.

A Boeing 787 Dreamliner flying over a river

Image source: Boeing.

Even when airlines start to grow again, they may not grow as quickly as they did over the past five years. In a presentation earlier this year, Boeing acknowledged that air travel expanded significantly faster than its historical growth rate over the past several years. Indeed, many airlines were struggling due to overexpansion even before the pandemic. The pandemic decisively popped this bubble in the aviation market.

The market share problem

Finally, Boeing shareholders have to reckon with a shift in market share toward Airbus. In 2018, Boeing delivered slightly more commercial jets than its European rival. Today, Airbus' order backlog is 73% larger than Boeing's.

Thus, aircraft demand is likely to remain dramatically below pre-pandemic levels for the next few years, even if a COVID-19 vaccine is widely distributed during 2021. Even when airlines do start growing again, they will probably grow more slowly than in recent years, causing aircraft demand to remain lower than 2018 levels. And Boeing is likely to hold a smaller piece of that smaller market over the next decade.

The impending arrival of COVID-19 vaccines is still good for Boeing stock. If vaccines hadn't become available for two or three years, it would have been catastrophic for Boeing. That said, vaccines aren't enough of a game changer to send Boeing stock on a rally back to its early 2019 high. The company's main business -- building commercial jets -- simply isn't likely to make a full recovery within the next decade.

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.