Every safe and effective Covid-19 vaccine is helping to end the global pandemic. But that doesn't mean they're all the same.

Some are harder to manufacture. Others are trickier to ship and store. There are one-dose and two-dose versions. And doctors in the United Arab Emirates found that the Chinese-made Sinopharm vaccine can require a third dose.

With its power and resources, the U.S. has an important role to play in getting the whole world immunized. To succeed globally, though, we can't just focus on what works best on our own shores. A temperature-sensitive vaccine shipped to a facility without freezers will go to waste. Scheduling two doses isn't feasible for every population. In developing countries, these challenges can be acute.

Which is why, in its vaccine diplomacy, the United States needs to prioritize one-dose, temperature-stable Covid-19 inoculations. Doing so could make an enormous difference in the speed and effectiveness with which we eradicate the disease.

The United States clearly has a moral responsibility to save lives. But it also has much to gain by helping to vaccinate the world. If unvaccinated "hot zones" persist, they will put herd immunity everywhere at risk. That will threaten livelihoods, as trade won't fully recover if the pandemic goes on. International air travel, for example, is both a boon to the global economy and a significant risk factor in the spread of the disease. The industry can't return to health as long as travel restrictions, quarantines, and fear of contagion continue.

The United States can also achieve a soft-power advantage through global health leadership, as it has in the past.

The PEPFAR initiative to check the spread of HIV/AIDS in Africa, which began under President George W. Bush, brought the United States huge dividends in goodwill. The United States also led the global response to the deadly Ebola outbreak in West Africa in 2014 and 2015, committing civilian and military personnel under President Barack Obama.

Today, other global powers also have the power to combat health crises abroad. China is in negotiations or has agreed to provide its domestically made vaccines to at least 13 governments in sub-Saharan Africa, while Russia is providing its Sputnik V vaccine to 15 countries in the region. Both Beijing and Moscow are eager to gain influence on the continent; Russia has gone so far as to mount online disinformation campaigns disparaging U.S.-made vaccines and touting its own.

A successful global vaccination campaign has to get the right shots to the right places. The first vaccines to win U.S. authorization, those made by Moderna and Pfizer-BioNTech, are complex to manufacture, require two doses, and must be stored at very low temperatures.

While highly effective, they are not viable in health care systems that can't maintain what is known as a "cold chain" -- a means to keep the shots chilly, even during transportation. And a two-dose vaccine doesn't work in places where patients live far from clinics, and health care workers have to deal with poor roads and not-yet-ready digital systems. Large parts of sub-Saharan Africa face these challenges.

But other Covid-19 vaccines solve these problems. The Johnson & Johnson inoculation requires only one shot, and can be kept at regular household-fridge temperatures for up to three months.

More remarkably, Akston Biosciences has begun human trials of a vaccine that can be transported and stored without any refrigeration, even in warm climates. The shot remains potent for one month stored at 95 degrees Fahrenheit -- and for at least four months at a balmy 77 degrees. It has the potential to transform global vaccine delivery.

Meanwhile, Vaxart is working on a Covid-19 vaccine in tablet form, and Altimmune is developing a nasal spray version. Either could be self-administered, which would dramatically reduce logistical hurdles. Other biotech companies are researching coronavirus inoculations that are more potent at lower doses or easier to modify against new variants.

As the U.S. decides which vaccines to fund, approve, manufacture, and donate, it can help lead the world out of the pandemic. Success will come through recognizing that there is no one-size-fits-all solution.

Drew Johnson is a senior fellow at the National Center for Public Policy Research. He regularly reports about, and consults on, economic development and human rights efforts in developing countries.