One of the toughest things about 2020 was the anxiety caused by the lack of a reasonable time frame for how long this pandemic will last. Thankfully, now that we have not one but multiple vaccines being rolled out across the world, we can see the light at the end of the tunnel. But how long is this tunnel?

In the most optimistic scenario, the transition towards normalcy, at least in the United States, seems to be the second quarter of 2021. By December 2021, life may return to normal in the sense that virtually all businesses will be open and travel will be allowed, although some restrictions may still apply going forward into 2022, such as wearing a mask in certain places.

However, this timeline may be disrupted by the emergence of new, vaccine-resistant strains or poor vaccine rollout. Bearing these risks in mind, the timeline for our exit out of the coronavirus pandemic will likely sit somewhere between a ‘best-case scenario’ and a ‘worst-case scenario’.

Optimistic scenario: Fall 2021

Anthony Fauci, the director of the National Institute of Allergy and Infectious Disease and President Biden’s foremost advisor on all matters related to the coronavirus, said that “some degree of normality” could be achieved through herd immunity as early as the fall of 2021. He did not go as far as to offer any guarantee though.

“There still may be enough [community] infection that you may not want to have theaters or entertainment venues open, but I think there is a reasonable chance that if we can get that percentage of people vaccinated, that we will be able to go to a movie or a theater [in the fall of 2021],” Fauci said in February.

For most of last year, whenever scientists were inevitably asked when life will return to “normal”, the standard answer used to be whenever we achieved herd immunity. Given the coronavirus’s infectiousness profile, that entails having 70% to 80% of the population immune to the coronavirus, whether thanks to vaccination or recent infection. Once again, Fauci reiterated that any recovery plan hinges on having enough people inoculated for herd immunity.

As of Monday, February 22, the Centers for Disease Control and Prevention claimed that about 44.1 million people have received at least one dose of a COVID-19 vaccine. Among them, 19.4 million were fully vaccinated with two doses.

On average, providers are administering about 1.6 million doses per day, up from about 1 million doses per day in January. When he took office, President Biden promised to administer 100 million vaccines by his 100th day in office, but later called for more than 1.5 million doses per day. Even so, critics feel this is not ambitious enough.

Achieving herd immunity would involve vaccinating around 300 million people, which means 600 million doses. Around 45 million doses have already been administered, which leaves us with 550 million. At the current rate, it would take the U.S. about a year, starting now, to achieve herd immunity at a national level, although some states, counties, cities, and local communities may achieve their local herd immunity much earlier than that, depending on their vaccine coverage and the previous number of infections.

In the best case scenario, in which all supply pledges are met and vaccines become eventually available for children, it may be possible for 80%-90% of the country’s population to be vaccinated by Christmas time.

As COVID-19’s impact on health wanes, there will be an increasing amount of normalization of social and economic life. Data on the availability of vaccine doses in the United States are encouraging and suggest that this is possible starting from the second or third quarter of 2021, but the slow start to the vaccine rollout reinforces that success is by no means guaranteed.

Not so optimistic scenario: 2022

The United States’ transition toward normalcy during the third quarter of 2021 is the likeliest scenario at this point, but this forecast may be derailed by a combination of poor vaccine logistics and new strains that may be less responsive to our vaccines.

Currently, 2 COVID-19 vaccines are available for immunization in the United States: Pfizer-BioNTech and Moderna COVID-19 vaccine. Both are mRNA-based vaccines that have close to 95% efficacy in preventing COVID-19 disease. However, new strains such as the so-called British and South African variants may lower this efficacy. A study published in January was reassuring, finding that Pfizer and BioNTech weren’t affected by these mutations.

However, this study was rather small. Another investigation that involved thousands of people found that AstraZeneca’s vaccine was only 22% effective at preventing mild disease, compared to an efficacy of 75% that it used to have for the original strains.  Novavax vaccine was found to have an efficacy rate of under 50% for the South African variant in a study involving 4,400 participants, compared to 86% against the British variant and 95.5% against the original coronavirus strain for the mild-moderate disease. Johnson&Johnson reported a 57% efficacy against moderate-to-severe disease due to the new variant, compared to 66% for overall protection against other strains.

However, it should be noted that AstraZeneca, Novavax, and J&J do not offer mRNA vaccines like Pfizer and Moderna, which may indeed still retain their initially reported efficacy. Even so, there may still be some trouble or at least delays caused by these pesky mutations.

Coronaviruses frequently mutate as they pass from human to human and, for the most part, don’t significantly alter the virus. Still, a handful of mutations in the British and South African variants appears to allow the virus to spread faster.

The threshold to achieve herd immunity is governed by a number of factors, including the transmissibility of the disease. Therefore, more infectious strains of the coronavirus will raise the bar on herd immunity.  Initial estimates suggest that the transmissibility rate of the UK strain is 40 to 80 percent higher than that of the original SARS-CoV-2 strain, and that transmission rates could be higher among children too.

Luckily, there is no evidence that these new variants also increase the fatality rate. Even so, they may reduce the efficacy of the vaccines and their increased transmissibility rate could extend the pandemic by months, well into 2022.

At some point, the trouble we’ll run into won’t have to do with mutated strains or vaccine supply, but rather with people’s willingness to become vaccinated. Surveys suggest that a portion of the population is cautious, skeptical, or downright unwilling to get a vaccine.

Getting vaccine coverage to 60 to 70 percent will be a lot easier than getting to 70 to 80 percent because that’s where we’ll likely hit an antivaxx wall.

A variant that is 40% to 80% percent more transmissible and considering a vaccine efficacy of 90% would require 83% to 100% of those over 12 to be vaccinated to achieve herd immunity. A vaccine with an efficacy of anything less than 75% would make herd immunity likely unachievable through vaccination of only those over 12, according to a McKinsey paper from January.

The light at the end of the tunnel

Despite concerns surrounding vaccine rollouts, anti-vaxxers, and new coronavirus variants, one thing’s for sure: we’re well past the hardest part of this pandemic.

Thanks to unprecedented efforts in vaccine development, we now have multiple effective products against the virus, which means it’s only a matter of time before we can return to our normal lives.

Of course, even if we’re close to herd immunity, don’t expect things to return exactly to the way the were. Expect ongoing monitoring, potential revaccationation programs, and the treatment of isolated cases going forward through the end of 2021 and 2022. However, these actions will fall more into the category of conventional infectious disease management rather than the society-altering, anxiety-triggering interventions we’ve lived through in 2020.