Yesterday we covered how the US needs to respond in the next 6 months in order to flatten the curve of Covid-19 cases and have a chance at preventing the worst possible outcomes of this pandemic.

Unfortunately, we’re already guaranteed to endure this for a long period.

Even a perfect response won’t end the pandemic. As long as the virus persists somewhere, there’s a chance that one infected traveler will reignite an outbreak elsewhere.

Remember this all started with one person.

We’re already seeing remission happening in China, Singapore, and other Asian countries that briefly seemed to have the virus under control.

Here’s the brutal truth: there are three possible endgames: one that’s very unlikely, one that’s very dangerous, and one that’s very long.

First, and regrettably most unlikely, every nation manages to simultaneously conquer the virus , similar to the original SARS in 2003. Given how widespread the pandemic is at this point a month after it was officially declared one, and how badly many countries are responding, the odds of worldwide containment are withering by the day and hour.

Second, and most dangerous, is that the virus accomplishes what the worst pandemics have: burn through the world until it leaves behind enough immune survivors that it eventually struggles to find viable hosts. This “herd immunity” scenario does have a positive, but morbid, result: it would be quick. It should be no surprise, though, that it would come at a terrible cost: SARS-CoV-2 is more transmissible and fatal than the flu, and it would  leave millions of corpses and a trail of devastated health systems. The United Kingdom initially seemed to consider this herd-immunity strategy, before backtracking when models revealed the dire consequences. The US is doing the same.

Third, and perhaps most realistically palatable, is that the world fights the virus for the next year, stamping out outbreaks here and there, until a vaccine can be produced. Some nations will fare better or worse depending on their response to initial contact and remission, but progress will come as the world rallies to mitigate and rebuild.

Importantly, all three possibilities need a vaccine to ensure Covid-19 is defeated. If this were a flu pandemic, we would have seen a vaccine much faster as the world is experienced at making flu vaccines and does so every year.

However, there are no existing vaccines for coronaviruses — until now, these viruses seemed to cause diseases that were mild or rare — so we are starting from very little.

Much like every other source of collective adversity we’ve faced as a species, conquering Covid-19 will come down to our ability to organize and innovate.

Our first steps have been impressively quick. Already a possible vaccine created by Moderna and the National Institutes of Health went into early clinical testing. That marks a 63-day gap between scientists sequencing the virus’s genes and doctors testing a vaccine candidate — overwhelmingly a world record, as Dr.Fauci put it.

But it’s also the fastest step among many subsequent slow ones. The initial trial will simply tell researchers if the vaccine seems safe and mobilizes the immune system correctly. That’s critical because a vaccine works by training the immune system to recognize and combat pathogens, such as SARS-CoV-2 which causes Covid-19.

The Covid-19 disease, and many like it, work by turning your own body and its defenses against you. However, if your body recognizes and destroys the pathogen before it has a chance to compromise your immune system, there are two primary benefits: 1. You don’t become immunocompromised, and 2. You don’t become a carrier for the virus, so other people (who might not be able to fight it) don’t get sick. That’s why a vaccine is so critical for stopping the spread: it’s less about not getting you sick, and more about denying a virus from being able to effectively spread through a population.

Unfortunately, vaccines are not easy, especially for a new virus like SARS-CoV-2. Researchers will then need to check that it actually prevents infection. They’ll then need to do animal tests and large-scale trials to ensure that the vaccine doesn’t cause severe side effects. Finally, they’ll need to work out what dose is required, how many shots people need, if the vaccine works in elderly people, and if it requires other chemicals to boost its effectiveness.

Essentially, while it would be wonderful for the vaccine to be in doctor’s hands tomorrow, this is not a process that is easily rushed — and for very good reasons.

It’s likely, then, that the new coronavirus will be a lingering part of American life for at least a year, if not much longer. If enough people maintain quarantine and the current round of social-distancing measures works, the pandemic may be reduced by enough for things to return to a semblance of normalcy sometime this year.

But it has to be gradual. As the status quo returns, so too will the virus.

It doesn’t mean we won’t see the sun again for years, but we may see multiple periods of extended social distancing, especially as we head back into winter. The coming years, including the frequency, duration, and timing of these mass social upheavals, are dependent on two unknown properties of the virus,

The first is its seasonality. Viruses tend to thrive in the winter when people stay inside and close to one another more, but they mostly disappear in the summer. That may also be true for SARS-CoV-2, but seasonal variations might not sufficiently slow the virus now that it is a worldwide pandemic and only those who have survived it are immune to it. That being said, with summer coming soon in the Northern Hemisphere, and with 88% of the world’s population living there, it stands to reason that we might see some reprieve. Importantly, however, is that it not allowed to see resurgence once the weather gets chilly again.

The second unknown variable of the virus is the duration of a survivor’s immunity. As we talked about regarding vaccines and how your body naturally fights off pathogens, you need to be exposed to the antigens present on all viruses and bacteria so your immune system can ‘learn’ what a hostile actor looks like and how to fight them with corresponding antibodies. That’s how a vaccine works, and why it’s so critical — it ‘teaches’ your immune system how to fight a virus you’ve never been exposed to before. Even if you do contract Covid-19 and survive, the important question is how long your immunity will last. When people are infected by the previously-seen milder human coronaviruses that cause cold-like symptoms, they remain immune for less than a year. By contrast, the few who were infected by the original SARS virus, which was far more severe, stayed immune for much longer.

Assuming that SARS-CoV-2 lies somewhere in the middle, people who recover from their encounters might be protected for a couple of years. To confirm that, scientists will need to develop accurate serological tests, which look for the antibodies that confer immunity. Most importantly, they’ll also need to confirm that such antibodies actually stop people from catching or spreading the coronavirus. If that’s confirmed, immune citizens can return to work, care for the vulnerable, and anchor the economy during bouts of social distancing.

It will be a series of changes we’ll all need to get accustomed to.

Here’s the good news: whether through us accumulating herd immunity or through the arrival of a vaccine, the virus will thankfully find spreading more and more difficult. More than likely, we’ll never truly be rid of it — just like common strains of the regular flu. Additionally, the Covid-19 vaccine will likely need to be updated as the virus changes, and people may need to get revaccinated on a regular basis, as they currently do for the flu. Models suggest that the virus might simmer around the world, triggering epidemics every few years or so.

My hope and expectation is that the severity will gradually decline once it hits its peak sometime over the next 3 – 6 months, and there would be less societal upheaval within a year.

In the future, Covid-19 will become like the flu is today — a deadly recurring scourge of winter that will still kill thousands every year, but will ultimately be a watered-down version of its previous ferocity. Perhaps it will eventually become so mundane that even though a vaccine exists, large swaths of Gen C won’t bother getting it — forgetting how dramatically their world was molded by its emergence.

Tomorrow we’ll wrap up this series by discussing the possibilities after the worst is behind us and it comes time to start putting society back together — and the massive inflection point in history that represents.