Vaccines can help end the coronavirus pandemic, but it’s impossible to put a clear timeline on their development. We will have to deal with the virus for the foreseeable future, and there’s no guarantee that we will have widespread vaccinations in 2021 or even 2022.

There is always a sense of optimism when we start writing about coronavirus vaccines. The unprecedented impetus, the huge sums invested, the numerous talented research teams — it all gives a sense of the world coming together and working towards a common goal.

We shouldn’t get carried away by a sense of exuberance, however. There are few guarantees when it comes to vaccines, and putting all our long-term eggs in the vaccine basket can end up backfiring if we don’t take other mitigation measures.

It typically takes a decade or so to develop a new vaccine. Of course, this is not your typical situation. More than 80 vaccine projects have kicked off around the world — an effort the likes of which has never been seen before. In this scenario, some immunologists have said that if everything goes right, we may have a vaccine in 12-18 months. As humans are inherently optimistic, we tend to interpret that as “we’ll have a vaccine in a year” — but that’s not what researchers are saying.

For starters, a vaccine needs to produce an immune response. This is the crux of any vaccine, but it’s far from being the only requirement. A vaccine also needs to be safe and not cause any significant side effects. Even when an immune response has been produced, and it is efficient in a large enough percentage of the population, it takes months and months of clinical treatments to ensure that the vaccine is indeed safe and effective — and there are no guarantees.

There’s no guarantee an immune response will be produced. There’s no guarantee that it will be safe. There’s essentially nothing to promise us that we will have a vaccine in a year, or two years, or any given time.

Then, even assuming we have a vaccine, scaling production for millions — or billions — of doses is not exactly a trivial task, especially in a struggling economy. It will take months if not years before a sufficient part of the population is immunized.

Considering all these factors, it’s easy to see a future where most of us don’t get a coronavirus vaccine in 2021 or even 2022. David Nabarro, Professor of Global Health at Imperial College, London, and an envoy for the World Health Organisation on COVID-19 recently said that we will have to live without the vaccine “for the foreseeable future” and our best chance is to adapt to it.

In an interview with The Observer, Nabarro said the public should not assume that a vaccine will definitely be developed soon.

“You don’t necessarily develop a vaccine that is safe and effective against every virus. Some viruses are very, very difficult when it comes to vaccine development – so for the foreseeable future, we are going to have to find ways to go about our lives with this virus as a constant threat.

“That means isolating those who show signs of the disease and also their contacts. Older people will have to be protected. In addition hospital capacity for dealing with cases will have to be ensured. That is going to be the new normal for us all.”

This doesn’t mean that we shouldn’t try to develop a vaccine; quite the contrary. The more vaccine projects there are, the greater the odds of actually developing one in a 12-18 month timeframe. But it’s just not certain. In a recent opinion article for The Guardian, Patrick Vallance, the UK government chief scientific adviser, said there are reasons to be optimistic about vaccines — but it will take time. How much time? Again, it’s hard to say.

The most optimistic version we’ve heard comes from Oxford scientists, who say that we may have a vaccine by September. The most pessimistic is that we’ll never have a vaccine. The reality is probably somewhere in between, but exactly where it lies on the axis between September and never, it’s hard to say. This “it’s hard to say” is a key element of our fight with COVID-19 — uncertainty is a key problem posed by the virus, and whether we like it or not, uncertainty is part of this challenge.