As wealthy countries make progress in their vaccination efforts, the temptation arises to imagine that the covid‑19 pandemic will soon be over. But the interconnectedness of global society—in combination with the unequal nature of vaccine distribution—could create a situation in which the pandemic persists for a very long time. Covid‑19 variants could develop in populations that have less access to vaccines than other populations have or in populations that refuse vaccination; such variants might have resistance to existing vaccines, potentially causing pandemic flare‑ups in countries where the pandemic had mostly ceased to be a problem. Quashing the pandemic could end up being a complex, frustrating process that stretches across many years as authorities struggle to vaccinate segments of the global population that are increasingly difficult to reach.

In the realm of business, the term long tail refers to selling small numbers of specialty items to a wide range of consumers with niche interests; this concept may provide an analogy for what the world will face in attempting to eradicate the covid‑19 pandemic once and for all. The long‑tail business strategy was very popular upon its emergence, but people soon realized that the strategy was so challenging to execute that pursuing it rather than pursuing the strategy of trying to develop products and services that appeal to mainstream markets was seldom very worthwhile. The current approach to covid‑19 vaccination is somewhat analogous to a mainstream-market strategy, with wealthy countries' currently focusing on vaccinating their entire populations as quickly as possible despite the challenges that the world's limited supply of vaccines imposes. But truly eradicating the pandemic requires countries instead to focus on the long tail—reaching the large numbers of individuals who are not as able (or as willing) to secure vaccines as the citizens of wealthy countries are. If countries fail to focus on the long tail, the pandemic could resurge again and again.

The interconnectedness of global society—in combination with the unequal nature of vaccine distribution—could create a situation in which the pandemic persists for a very long time.

New variants of the virus that causes covid‑19 have emerged in Brazil, the Philippines, South Africa, the United Kingdom, and the United States. Vaccines currently in use are less effective against some of these variants than they are against the initial strain of the virus. The South Africa variant has shown the capability to infect people who have already contracted and recovered from covid‑19. Brazil has suffered heavily from covid‑19, and some of the country's regions have experienced infection numbers that should have been high enough to produce herd immunity—a status in which so much of the population has had the virus that it runs out of new hosts to infect and ceases to be problematic. However, evidence from Manaus, an exceptionally hard‑hit city in western Brazil, now suggests that herd immunity may be much more difficult to reach than scientists had expected—particularly in light of the new covid‑19 variants that keep emerging.

Experience so far suggests that covid‑19 may not simply burn itself out in the poorer countries that are unable to access vaccines because wealthier countries are consuming all the available supplies as quickly as possible. Rather, the countries where the virus remains prevalent may have ongoing problems with infections and may give rise to one new variant after another. These variants can then spread around the world, potentially infecting the vaccinated populations of wealthy countries. According to a recent estimate from the Economist, the world's poorest countries will be unable to secure enough vaccine doses to vaccinate their populations against covid‑19 until at least 2024, and some countries might never be able to achieve full vaccination. Besides the logistical problems in distributing vaccines to people in poorer countries, global vaccination rates have heavy constraints because of limited production capacities for vaccines. The vaccines from Pfizer (New York, New York) and BioNTech (Mainz, Germany) that have very high effectiveness against multiple covid‑19 strains have been very difficult to produce, requiring special reagents and expertise that have never before existed at large scales. Although other vaccines are becoming available, their rollouts have been slower. Apparently, no signs indicate that the world will have enough covid‑19 vaccine for everyone anytime soon.

Even in wealthy countries that have plenty of vaccines to go around, the task of vaccinating enough citizens to stop the covid‑19 pandemic has its own long‑tail problem. Significant portions of the population in wealthy countries are skeptical of the vaccines and refuse to take them. In the United States and some other countries, covid‑19 vaccination has become a political issue rather than a public-health issue, complicating the vaccination situation further. Other nations, such as Russia, have very high percentages of people who do not trust that the vaccines the government provides will be safe and effective. The experience from Manaus hints at the risks that may lie ahead when wealthy countries run out of citizens who are eager to take vaccines. When wealthy countries reach this point, they will need to find ways to address the problems of vaccine refusal directly.

Polls have shown strong support in the United States for measures that would ban unvaccinated people from participating in some aspects of public life; however, the unique political system in the United States makes such measures difficult to enforce. The US government system distributes powers between its central government and state governments, which has made an effective pandemic response difficult to execute. And because people in the United States can travel easily from one state to another, states with poor prevention measures (or large populations of vaccine refusers) may serve as reservoirs for new vaccine-resistant covid‑19 variants, leading to recurring infections worldwide.

The problematic nature of covid‑19 vaccination is unlikely to change. Wealthy countries are very unlikely to pursue a strategy that prioritizes effective vaccination of the global population over a strategy that focuses on vaccinating as many of their own citizens as possible as quickly as possible. But nations' prioritizing the world first and their own citizens second might be the best way to combat covid‑19 effectively. As the impacts of global warming increase, governments of wealthy countries will face a similar situation in which coordinated global action is the only effective way to address a major crisis. If the covid‑19 response is any indication, those governments will be unable to rise to that challenge as well.