The most important lesson of the Covid pandemic is that the only constant is change. Variants spread, cases surge and abate, treatments change and knowledge expands. This means that we — the public, elected officials and public health leaders — need to learn constantly and adapt quickly, acting on the insight that no one policy response is likely to stay effective for long. Now is the moment to put that flexibility into practice. Rising Covid cases in Europe, the toll Omicron is taking particularly on unvaccinated elderly people in Hong Kong and slowing vaccinations are warnings that another wave of infections is likely approaching the United States. But we are by no means helpless. We can prepare better, save lives and reduce disruption. Although the exact reasons for the rapid increase in cases in Europe aren’t known, it almost certainly results from a combination of the highly infectious BA.2 Omicron subvariant, changing public behavior and waning immunity. BA.2 is making up an increasing proportion of new cases, and is extending the Omicron surge. At the same time, countries in Europe are lifting Covid-19 restrictions, including mask mandates and indoor capacity limits, and immunity to infection from vaccines and possibly also from prior infections is waning. Thankfully, although protection against infection through vaccination is something of a flash-in-the-pan phenomenon, the protection vaccines provide against severe infection and death is more durable. We’ve also learned more about the nature of the threat. It has been an open question whether Omicron is a much less severe variant of the Covid virus than earlier strains, or if it has caused much less severe disease because it had run into a wall of immunity from vaccination and prior infection in the United States, Europe and parts of Asia with high vaccination rates. The deadly outbreak in Hong Kong answers that question: Covid remains ferocious, and Omicron is lethal in an immunologically naïve population, particularly among unvaccinated older people. This has caused the devastating surge in deaths there and helps explain why the United States continues to report around 1,000 deaths per day, the vast majority among people not up-to-date with vaccination. Unfortunately, in the United States and many other high-income countries, vaccination has slowed to a trickle: It’s down in the United States by more than 95 percent from the peak of 4 million vaccinations a day. In some countries of Africa, where competing health risks are substantial and the health care infrastructure is stretched thin, vaccination rates are very low and are likely to remain so for many months. The risks for the United States are clear. BA.2 is increasing and will likely soon account for most new cases in the country. Masks have come off and approximately 60 percent of Americans, including more than one third of people above age 65 — more than 15 million seniors — are not up-to-date with vaccination. This doesn’t mean that BA.2 will inevitably cause a deadly surge. But it does mean that cases may increase soon, and that unvaccinated and under-vaccinated elderly and medically vulnerable people could face a deadly threat. Leaders need to redouble efforts to get more Americans, particularly older adults, vaccinated and boosted. Also, people who are older or immunocompromised and those around them should consider masking with a more protective N95 or equivalent mask. Increasing access to rapid testing could blunt the case increase by isolating people faster and linking those who test positive to rapid treatment with medications which drastically reduce the risk of severe illness. Improving vaccination rates may be harder with the rollback of vaccine mandates, which increased vaccine uptake and saved lives. With vaccine mandates politically or legally infeasible in some places, other strategies become increasingly important. These include ensuring that every physician offers Covid-19 vaccination to every patient at every clinical visit. Outreach programs and media campaigns can engage people without a regular doctor or who are otherwise not receiving care. Providers and health systems should reach out to every Medicare patient who may not be up-to-date to schedule vaccination. Repeated Covid surges have thrown into relief the underlying weaknesses and chronic underfunding of our public health and primary health care systems. Infectious diseases emerge where society fails. Lack of trust limits the ability of governments to protect their people. Weak public health systems mean that new threats are discovered when it’s too late to take action. Sustained funding can help ensure Americans are protected from future pandemic threats by allowing permanent budget-cap exemptions for critical health defense functions rather than relying on transient supplemental funding for each health emergency. Until US primary health care systems are much more robust, diagnosis, treatment and vaccination against Covid and other threats will remain lacking, allowing Covid to spread, and to do so among populations that are far less resilient than they would be if people received good preventive care. “Follow the science” is a mantra, but science can be painfully slow and decisions inevitably need to be made before perfect information is available. We don’t yet know what’s driving the emergence of variants or what future variants will bring. Nor do we know the optimal vaccination schedule for different groups, whether a fourth dose will be needed, and, if so, for whom and when. And we don’t know whether the highly effective treatments that have been discovered, on which the Biden administration is betting heavily, can reach enough people to greatly reduce hospitalizations and deaths. The struggle to get even half of eligible Americans up to date with vaccination doesn’t bode well for widespread treatment; treatment is generally much more difficult to scale than vaccination. Even so, we must try. Public health, like politics, is the art of the possible. Rigorous epidemiology, meticulous response management and well-communicated science need to be the foundation of public health action. Increasing vaccination, including boosters, among older and vulnerable people is a life-or-death challenge. Scaling up the linkage of testing to treatment can reduce hospitalizations and deaths substantially and protect health care systems. The United States also needs to support faster detection and response systems nationwide and globally. As a supplement to strengthening other tracking systems, monitoring for Covid in wastewater, as is done for polio and other diseases, may identify disease spread before many people become ill. If public health professionals find outbreaks right as they start, leaders can limit spread. For now, most of us can enjoy the warm spring sun on our unmasked faces. But we can also do a lot more to control Covid. If we learn quickly and act quickly, we can outmaneuver the virus. As Covid continues to adapt, our response needs to adapt along with it. We could be entering the endgame for Covid. How we play it will determine what happens next. The New York Times