As the BA.2 wave reaches its peak in the UK and begins subsiding in some European countries, US health officials are looking to an uncertain future even as American lawmakers have delayed renewing funds to address the pandemic.

While the Omicron subvariant now makes up an estimated 72% of Covid cases, the US has not seen a country-wide increase in cases. Covid hospitalizations are now at the lowest point of the pandemic.

But scientists warned this week that the coronavirus will continue evolving to evade immunity, causing future surges that will be difficult to predict.

Covid-19 has evolved faster than expected, and “we should expect a lot of evolution going forward,” Trevor Bedford, a professor of biostatistics at the Fred Hutchinson Cancer Center, told a panel of independent FDA advisers on Wednesday. “Those viruses will do better and will spread locally and perhaps regionally and perhaps globally.”

The US has generally followed surges in the UK three or four weeks later, but reported cases are holding steady at an average of about 26,000 a day. Although deaths have declined significantly from the Omicron peak, more than 500 Americans are still dying every day.

“I think we are going to see some rising cases in some places,” said Benjamin Linas, professor at the Boston University School of Medicine. Lifting precautions will probably result in future upticks, he and others wrote in a study published earlier this month.

“We’re not in the crisis that we were back in 2020, but we need to be realistic that we’re also not completely over and done,” Linas said.

Some regions in the north-east, including New York and Massachusetts, are beginning to see ticks upward. Philadelphia is considering a return to indoor masking next week.

In Washington DC, where confirmed cases have increased by 135% in the past two weeks, several high-level politicians have tested positive, including the House speaker, Nancy Pelosi, on Thursday.

It’s difficult to parse the extent to which surges elsewhere have been driven by changes in behavior, BA.2’s increased transmissibility, and waning immunity, and whether factors in the US could suppress such a wave.

As the pandemic wears on, changes to how cases are reported and counted may also cloud the picture.

Home tests are frequently not counted in official tallies, making it increasingly difficult to understand how widespread infections are. Wastewater monitoring could be useful to fill in the gaps, but many places are still ramping up such programs.

Several states have moved to weekly or twice-weekly, instead of daily, reporting of cases, mirroring a similar shift in June 2021 during a lull before the Delta surge. Oklahoma is changing how it reports its seven-day average of cases.

Changes to definitions of Covid hospitalizations and deaths may also complicate pandemic tracking.

Some states have also narrowed their definitions of Covid hospitalization to focus only on patients receiving Covid-specific medications, while others have changed how they define Covid deaths.

Last Monday, US lawmakers reached a deal for $10bn in Covid funding, some of which has already lapsed. But on Thursday, several senators confirmed that the vote will not take place until after the upcoming two-week spring break.

This amount was lower than the $15bn previously cut from an omnibus spending bill or the $22.5bn requested by the White House.

The new bill will not cover tests and treatments for those without insurance, who lost that coverage in March. More than 30 million Americans aren’t insured, and the lack of affordable, accessible testing and treatments could further affect the country’s ability to track and address cases and severe illness.

The new funding package would also cut spending for global Covid campaigns, including vaccination, which could prolong the pandemic by allowing new variants to emerge and spread.

“This is a global health problem, and if we continue to cut the budget for vaccines in developing countries, we’re going to get the next Omicron,” Linas said. “Because we have these pockets where the virus goes to reproduce, it’s already extended the epidemic by at least a year – and if it keeps on happening, we’re going to chase our tail indefinitely.”

An estimated half of Americans may have been infected with Omicron in a 10-week period – a “remarkable number”, Bedford said. In comparison, influenza usually infects perhaps 10-20% of the population in about 20 weeks.

But that would also mean that about half of Americans weren’t infected in the first Omicron wave, potentially leaving them vulnerable to another surge now. The coronavirus, as it swept the globe and infected millions, mutated two to 10 times faster than influenza usually does, Bedford said.

It’s likely that future variants will still emerge from Omicron, even overcoming immunity from previous cases of Omicron, he added.

But there’s also the potential for the wildcard emergence of a new variant from a previous strain, like Delta. Omicron seems to have evolved from a much earlier version of the virus in summer 2020 before exploding across the globe in late 2021.

It’s also difficult to understand if Covid-19 will eventually become a seasonal virus, like influenza or respiratory syncytial virus (RSV).

“It’s not clear to me that it’s actually tied to the months of the year, or if that’s just confounded by the virology that’s been happening,” Linas said. Influenza, for example, is “highly seasonal” but “I don’t think we know that yet about Sars-CoV-2.”

One major treatment has been halted in the US amid questions of its efficacy. The US Department of Health and Human Services (HHS) pulled its authorization of sotrovimab, a monoclonal antibody, as studies reveal it is less likely to be effective against Omicron. Recent research also indicates that this treatment might create resistance – a major concern with other monoclonal antibodies and antivirals.

Vaccines and treatments help, but they aren’t sufficient to halt the pandemic on their own, and they must be accompanied by measures like ventilation and masking during times of high transmission, Linas said.

Surges are also highly dependent on human behavior.

“There is no virus epidemic outside the context of the way people behave,” Linas said. “It would be a big mistake to let off on ourselves and our leaders … The actions we take or don’t take matter a ton.”