A slow and steady increase in box office receipts could be threatened by a new variant of the coronavirus.

The domestic box office has gained momentum since March, bringing in up to $ 98.7 million in ticket sales last weekend, a record during the pandemic era.

Around 80% of the cinemas are open to the public this weekend, and mask restrictions on those who have received the coronavirus vaccination have been relaxed. With cinemas opening wider and Covid cases falling, studios have been confident of releasing big blockbuster pictures.

Last weekend, Universal’s “F9” hit the highest opening weekend of any movie released during the pandemic for a grand total of $ 70 million and helped increase total weekend loot to $ 98.7 million, another record for the industry .

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More than half of the US population has received at least one dose of the vaccine, which has resulted in a sharp decrease in the number of deaths from Covid, according to the Centers for Disease Control and Prevention. The number of new cases had fallen significantly in the last few weeks and is still well below its peak. However, public health officials are watching the spread of the highly contagious Delta variant in communities with low vaccination rates, which has led to a surge in cases recently.

It is feared that an increase in the cases of Delta variants could lead to a resurgence of health and safety restrictions not only domestically but also internationally and discourage worldwide moviegoers from going to the movies.

Cities like Los Angeles have already chosen to reverse mask guidelines and strongly recommend that both unvaccinated and vaccinated individuals wear masks in public places such as restaurants, shops, and movie theaters. Cinema chains have told CNBC that cinema locations will continue to comply with all local regulations.

“Each state is loosening mask strategies so many companies could be affected if it flares up,” said Eric Handler, media and entertainment analyst at MKM Partners. “I hope the vaccines can help fight it off enough that it’s not a big problem.”

CDC director Rochelle Walensky said Wednesday that the US has a high vaccination rate and its highly potent vaccines have allowed them to relax mask restrictions and social distancing measures. In comparison, much of the world is still unvaccinated and there is currently evidence that vaccines developed outside of the United States have been less effective.

“The global outlook also remains important as studios and exhibitors closely monitor key international markets and the evolution of their various vaccine distributions in the second half of the year,” said Shawn Robbins, chief analyst at Boxoffice.com.

In some countries where the Delta variant is on the rise, new lockdown measures have been imposed.

The Delta variant currently accounts for about 25% of the new cases sequenced in the US, and officials believe it will become the dominant strain in the country. In some counties, the delta variant rates are up to 50% according to the CDC.

The US government is concerned about parts of the US where vaccination rates are low. Domestically, about 1,000 counties in the United States have a vaccination coverage rate of less than 30%, Walensky said Thursday. These counties are mainly in the Southeast and Midwest and are the most prone to getting Covid infection, she said. The authority already sees increasing disease rates in these districts due to the further spread of the more transmissible delta variant.

“The movie industry, like many others, has been considering variant scenarios similar to the current one under the reopening plans and nothing is taken for granted,” said Robbins. “At this point, however, there is no evidence of an immediate impact on domestic cinemas as long as the vaccinated individuals remain protected, as health officials have widely reported.”

– CNBC’s Rich Mendez contributed to this report.

Disclosure: Comcast is the parent company of NBCUniversal and CNBC. NBCUniversal is the distributor of “F9”.