While the number of COVID-19 cases, hospitalizations and deaths have fallen from their peaks in the U.S., and the vaccine rollout underway, scientists have also warned that the next few months could be painful as several more contagious variants of the coronavirus are spreading in the country. 

According to the U.S. Centers for Disease Control and Prevention (CDC), there are currently five virus variants of concern in the country, which appear to be spreading more easily and quickly than other variants. The five identified are:

B.1.1.7: The variant was initially detected in the UK. It was first identified in the U.S. in December 2020.

B.1.351: The variant was initially detected in South Africa. It was first identified in the U.S. at the end of January 2021.

P.1: This variant was initially identified in travelers from Brazil. It was first detected in the U.S. in January 2021.

B.1.427 and B.1.429: These two variants were first identified in California in February 2021.

Already, B.1.1.7, which is 60 percent more contagious and 67 percent more deadly than the original form of the virus, is rising exponentially in the U.S. As of March 13, this variant alone accounted for about 27 percent of new cases nationwide, the New York Times reported. 

Other variants are also worrisome, because they contain a mutation that compromises the effectiveness of vaccines, according to health experts. 

"The best way to think about B.1.1.7 and other variants is to treat them as separate epidemics," Sebastian Funk, a professor of infectious disease dynamics at the London School of Hygiene and Tropical Medicine, told the New York Times.

Although most vaccines appear to be effective against the variants, public health officials are deeply worried that the virus will continue mutating and future mutations may be more resistant to immune responses. 

Infections are rising again in the U.S. since mid-March because of the variants. As of April 3, the daily number of new cases was up to nearly 69,000, and the weekly average was 19 percent higher than the figure two weeks earlier, the New York Times reported.