Americans marked their nation’s 245th birthday on Sunday with fireworks, hotdogs, marching bands and a sense of great relief, after the coronavirus pandemic forced the cancellation of nearly all celebrations last year.

As they did so, a senior administration official sought to explain why vaccinations and masks would not be mandatory for a major White House party, when he and other advisers to Joe Biden were stressing the need for Americans to lessen the chances of a surge in cases of the infectious Delta variant.

Speaking to CNN’s State of the Union, coronavirus coordinator Jeff Zients said: “You’re protected if you’re vaccinated. You’re not protected if you’re not. We are not mandating vaccines.

“At the White House tonight, there’s very rigorous testing and screening protocols. Those who are vaccinated do not need to wear a mask. Those who are unvaccinated do need to wear a mask.”

A day after the 78-year-old president mingled with mostly maskless crowds at a cherry-picking festival in Michigan, around 1,000 people were invited to his Fourth of July celebration on the White House lawn.

“We’re there to celebrate frontline workers and our military,” Zients said. “And these are people who understand the importance of safety and doing the right thing. I think most of these folks are vaccinated, and we encourage all Americans to get vaccinated as soon as possible.”

Asked why vaccination was not mandated, Zients said: “At the end of the day, it’s an individual choice. We hope all individuals make the right choice here and get vaccinated as soon as possible.”

Speaking to ABC’s This Week, Zients insisted: “The event at the White House is being done in the right way. It’s an outdoor event with testing and screening. Vaccinated people not wearing masks. Unvaccinated people masked. It’s being done in the right way, consistent with [Centers for Disease Control and Prevention] guidelines.

“That said, we are doubling down on our efforts across the summer months, we will vaccinate millions more people because you need to get vaccinated to be protected against the Delta variant and against this disease overall.”

The Biden administration missed its aim of having 70% of adult Americans with at least one shot by the holiday weekend.

Elsewhere on Sunday, chief medical adviser Anthony Fauci warned of likely spikes of cases of the Delta variant in areas with low vaccination rates, often due to resistance among Republicans loyal to former president Donald Trump.

In the first year of the pandemic, Trump staged a number of White House events with imperfect public health measures, followed by increases in Covid cases. Trump himself was hospitalised, reportedly with a more serious case than admitted.

Biden was scheduled to address his own White House event, on the theme of “Independence Day and independence from Covid-19”. According to excerpts of his remarks, he would herald his administration’s success in driving vaccinations, and to “urge every American to join the fight – to roll up their sleeves and get vaccinated”.

After dark in Washington, the National Mall was due to host a major fireworks show, a 17-minute cannonade from the Lincoln Memorial. On Capitol Hill, marching bands staged a traditional parade. New York was also set to host a major fireworks event, for which more than 65,000 shells were loaded on to barges in the East River.

In Ocean City, Maryland, fireworks were unintentionally detonated as they were being set up, leaving employees of a fireworks company with minor injuries, authorities said.

Numerous videos posted to social media showed fireworks popping and crackling near a crowded beach. No beach or boardwalk patrons were injured, the fire department said. The city said fireworks shows in multiple locations were canceled.

Some classic events with a national profile, such as Nathan’s Famous Hot Dog Eating Contest in Coney Island in Brooklyn, remained scaled back to allow for social distancing in recognition of a pandemic which has killed more than 605,000 in the US.

In Florida, several cities canceled fireworks out of respect for the victims of the building collapse in Surfside, near Miami, last month. Trump went ahead with a rally near Sarasota on Saturday, despite reported suggestions from aides to Governor Ron DeSantis that he should not do so.

It was expected to be the busiest Fourth of July for car travel, with an estimated 43.6 million hitting the roads, 5% up on 2019, the American Automobile Association said.

But for some, Fourth of July was still a somber occasion. In addition to the pall of the pandemic and the Florida building collapse, the western US faces a heightened risk of wildfires after a heatwave and amid extremely dry conditions.

The Department of Homeland Security, meanwhile, warned state and local police this week of a heightened threat of violence by domestic extremist groups.