ANAHEIM, Calif. — Orange County health officials recently reached a major COVID-19 vaccination milestone but didn't want residents to let their guard down ahead of a busy travel holiday weekend.

As the Fourth of July approaches, with millions expected to travel and gather despite the ongoing pandemic, Orange County health officials urge residents to remain cautious due to a new variant of COVID-19. Scientists and health officials consider the so-called Delta variant, a mutation of the COVID-19 virus, far more contagious than other COVID-19 strains.

"We know that other parts of the world are experiencing a new surge in COVID cases, often related to the Delta strain, which has been found to be highly transmissible," said Dr. Regina Chinsio-Kwong, deputy county health officer at the Orange County Health Care Agency in a statement. "In recent weeks, the Delta strain represents an increasing proportion of positive tests in the U.S., California, as well as in Orange County."

Chinsio-Kwong said the current COVID-19 vaccines, Moderna, Pfizer, and Johnson & Johnson, are effective against the Delta strain and other variants.

"This is another reason why we are encouraging people to get vaccinated if they haven't already done so," she said.

The warning comes after Orange County health officials reported reaching their goal of having 70% of residents ages 18 and over in the county with at least one COVID-19 vaccine shot before the Fourth of July holiday.

While Orange County health officials celebrated the county's vaccination milestone, they remain cautious as a new COVID-19 variant surfaces in the U.S. – and Orange County – just as millions of pent-up people expect to travel and gather this holiday weekend. Los Angeles health officials have already issued a statement strongly recommending residents to wear face masks indoors until more is learned about the new mutation. 

According to AAA, more than 47 million people expect to travel this weekend, "the second-highest Independence Day travel volume on record, trailing only 2019."

Anaheim, the home of Disneyland, is No. 2 on AAA's list of top travel destinations for people this weekend. Several cities across Orange County are also hosting 5K runs, community picnics and firework celebrations this weekend. California fully reopened its economy on June 15.

Orange County has seen a slight uptick in its seven-day COVID-19 positivity rate, said Dr. Clayton Chau, the Orange County Health Care Agency's director. More than 90% of new positive cases were from people not fully vaccinated, he said.

"Vaccination has proven to be a vital component in reducing test positivity rates in our county over the last several months," said Chau. "We know the vaccines work. We are continuing to offer them to our community and encourage everyone who [is] not vaccinated to do so."

Orange County health officials advise residents to continue practicing safe measures such as wearing a face covering, avoiding large crowds and following other guidelines from the Centers for Disease Control and Prevention.

And if people have symptoms of COVID-19, they're advised to get tested.

"If you have symptoms, whether or not you have been vaccinated, we encourage you to order a free test," Chinsio-Kwong said. "Testing allows us to identify variant strains, assist others who may be infected and take proactive steps to contain the disease."