William Haseltine is a former Harvard Medical School professor and founder of the university’s cancer and HIV/AIDS research departments. He serves as chair and president of the think tank ACCESS Health International.

A curious case of optimism — dangerously unfounded, I fear — has permeated our public discourse on covid-19, even as cases surge. Media outlets, even those that have long highlighted the severity of the pandemic, are now fixated on the hopeful, noting that deaths have not yet surged and that vaccines are working to prevent severe disease.

These are welcome facts indeed. But our enthusiasm for what is going right is limiting our ability to appreciate how badly things can still go wrong.

A new report from Britain’s Scientific Advisory Group for Emergencies (SAGE) warns there is no end to bad with this virus. It is a remarkable shape-shifter, able to mutate every nucleotide of its genome hundreds of times over in every infected person. Given this evidence, the study warns that the emergence of new variants that can evade vaccines and that may be as lethal as Middle East respiratory syndrome, killing more than 3 of 10 infected, is not just theoretically conceivable but a “realistic possibility.”

The study also suggests that the widespread deployment of vaccines has created new selection pressures that could increase the transmission advantage of a variant. Think of the virus as a highly tuned artificial intelligence machine, constantly mutating and adapting until it lands on a combination of mutations that gives it the upper hand. The fear is that when more people have vaccine-acquired immunity, the virus has more opportunities to adapt. This is in no way an argument against vaccination; we need immunity now to blunt the virus’s effects. But it is a warning that a single global round of vaccinations is unlikely to contain this virus forever. The study argues the countdown has started on the emergence of a vaccine-busting variant.

I, like most people I imagine, would prefer to ignore the SAGE study and other warnings like it. But the paper reminds us that everything is a moving picture, and whatever comfort we feel today may only be short-lived. We must prepare for and try to prevent the worst of what could come.

The SAGE experts provide some recommendations, which I fully support. First, they call for increased research on vaccines that can not only reduce the likelihood of severe disease but also the likelihood of infection and onward transmission of the virus. This is especially urgent given the recent data from the Centers for Disease Control and Prevention on breakthrough infections among those vaccinated. I would also stress the need for research on pancoronavirus vaccines that are capable of defending against a broader spectrum of coronaviruses and covid-19 variants.

The SAGE study authors also recommend enhanced vaccination efforts worldwide to drive down the global viral load and reduce the likelihood of variants emerging from other parts of the world. To this I would add other known strategies to drive down viral load beyond vaccinations, including mask-wearing, social distancing, widespread rapid testing, contact tracing and mandatory quarantine. And, when necessary, targeted lockdowns to contain the scope of new outbreaks and the spread of new variants.

The use of antiviral drugs to treat those who fall ill and prevent the further spread of disease is also addressed in the study, though the authors urge caution regarding the potential for drug resistance and the use of antivirals in immunocompromised people, which may eventually lead to new, more dominant variants. From my own experience working on HIV treatments, I second these notes of caution while reinforcing how critical combination drug therapies could be to reducing the scope of the pandemic if used to prevent illness. The same warp speed effort we put behind vaccines should be powering our search for safe and effective antiviral cocktails and combination therapies in pill form.

None of these strategies will be enough to counter this virus on their own. To protect ourselves from the worst of what it has to offer, we must use a multimodal strategy that combines the best of what we have on hand. This includes antivirals, vaccines and public health strategies, for sure, but also long-term, global strategies on genomic surveillance, research on the potential evolution of this virus and others like it, and an unwavering focus on developing second- and third-generation vaccines and treatments.

Beyond this, we need to accept that, whether we like it or not, we live in a world full of viruses. We can’t eliminate all viral threats, but we can build a culture of care that can help protect us from many diseases. In the same way we walk through a forest with an eye to the ground for poison ivy, so too should we walk through our days: aware of the risk of, for example, a public transit commute and adopting mitigative strategies.

Hope and optimism can be powerful motivators. Today, these forces compel us toward greater vaccination rates. But hope, we must remember, was also the last evil left in Pandora’s box. This virus is a mighty opponent, and we have underestimated it at every step. Hope that we are winning the battle today may prolong the war tomorrow as we pull down our masks, relax our defenses and open up new avenues for attack.