Massachusetts officials have purchased 2.1 million at-home COVID-19 tests to give for free to 102 towns with the highest percentage of people below the poverty level, Gov. Charlie Baker said.

The tests come in packs of two and can be completed at home in 15 minutes.

"Each city or town will be able to determine how best to distribute tests within their community," Baker's office said in a statement Monday.

Philadelphia restaurants will require proof of vaccination beginning on Jan. 3, city officials announced.

The mandate applies to anywhere selling food, including bars, movie theaters and sports venues.

"New cases and hospitalizations are rising, and we must do more to protect our residents," Mayor Jim Kenney tweeted.

From Jan. 3 to Jan. 17 there will be a grace period, during which patrons can show proof of a negative test. But after Jan. 17, all patrons must show their vaccination status, officials said.

The omicron variant appears to have a "growth advantage" over the delta variant, the World Health Organization said in a technical brief released Sunday.

"It is spreading faster than the delta variant in South Africa where delta circulation was low, but also appears to spread more quickly than the delta variant in other countries where the incidence of delta is high, such as in the United Kingdom," the WHO said in the brief, which was dated Friday. "Whether omicron's observed rapid growth rate in countries with high levels of population immunity is related to immune evasion, intrinsic increased transmissibility, or a combination of both remains uncertain. However, given the current available data, it is likely that omicron will outpace the delta variant where community transmission occurs."

Meanwhile, preliminary findings from South Africa suggest omicron may cause less severe illness than delta, and all cases of omicron reported in Europe to date have been mild or asymptomatic. But the WHO said "it remains unclear to what extent omicron may be inherently less virulent" and that "more data are needed to understand the severity profile."

The WHO also noted that "there are limited available data, and no peer-reviewed evidence, on vaccine efficacy or effectiveness to date for omicron." However, preliminary evidence, and the considerably altered antigenic profile of the variant's spike protein, suggests a reduction in vaccine efficacy against infection and transmission associated with omicron.

"There is some preliminary evidence that the incidence of reinfection has increased in South Africa, which may be associated with humoral (antibody-mediated) immune evasion," the WHO said.

The diagnostic accuracy of routinely used polymerase chain reaction (PCR) test and antigen-based rapid diagnostic test (Ag-RDT) assays does not appear to be influenced by omicron. Therapeutic interventions for the management of severe or critical COVID-19 symptoms associated with omicron are also expected to remain effective, according to the WHO.

"However, monoclonal antibodies will need to be tested individually, for their antigen binding and virus neutralization and these studies should be prioritized," the WHO added.

-ABC News' Christine Theodorou

South African President Cyril Ramaphosa is receiving treatment for "mild COVID-19 symptoms" after testing positive for the virus on Sunday, his office said in a statement.

Ramaphosa, 69, began feeling unwell earlier Sunday after leaving a state memorial service in Cape Town in honor of Frederik Willem de Klerk, South Africa's last apartheid president and a Nobel laureate, who died last month. Ramaphosa, who is fully vaccinated against COVID-19, was experiencing "mild" symptoms and a test confirmed he was infected, according to his office. The statement didn't say whether he has the omicron variant, which was discovered by scientists in southern Africa last month and is spreading rapidly.

Ramaphosa is self-isolating in Cape Town and is being monitored by the South African Military Health Service. He has delegated all his responsibilities to Deputy President David Mabuza for the next week, his office said.

Last week, Ramaphosa traveled with a delegation to four West African nations. He and the members of the South African delegation were all tested for COVID-19 in each of the countries during their trip. They returned to South Africa on Dec. 8, after testing negative in Senegal. Ramaphosa tested negative again upon arriving in Johannesburg that day, according to his office.

The statement advised people who had contact with the South African president on Sunday to watch for symptoms or to get tested for COVID-19.

"President Ramaphosa says his own infection serves as a caution to all people in the country to be vaccinated and remain vigilant against exposure," his office said in the statement. "Vaccination remains the best protection against severe illness and hospitalization."

-ABC News' Christine Theodorou

School leaders at both New York University and Princeton University announced Wednesday that they will take steps to cancel end-of-year events and move winter exams online amid a surge in COVID-19 cases on their respective campuses.

"Given that we've seen an uptick in cases among undergraduates during the last 24 hours -- including suspected cases of the highly contagious Omicron variant -- we hope to avoid letting the final exam schedule interfere with students’ travel home for Winter Break," Princeton University's dean, Jill Dolan, and vice president for campus life, Rochelle Calhoun, said in a joint statement. "We certainly don’t want you remaining on campus in required isolation through the holidays."

All indoor gatherings with food and those where face coverings cannot be worn must be canceled or postponed at Princeton's New Jersey campus from Thursday through Jan. 7, according to the statement.

A statement from New York University's provost, Katherine Fleming, executive Vice President, Martin Dorph, and head of the COVID-19 prevention and response team, Dr. Carlo Ciotoli, said they "strongly encourage that final examinations and/or assessments be changed to remote/online format." All discretionary, non-essential, non-academic gatherings and events at the school's campus in New York City must be canceled "immediately," according to the statement.

"The continuous review of the data from our COVID-19 testing program has indicated a considerable acceleration in the rate of new cases in our community," they said. "It’s not a cause for alarm, but it is a cause for concern, caution, and appropriate actions."

NYU has also joined a growing list of colleges and universities across the nation that are requiring all eligible members of the school community, including faculty and students, to be fully vaccinated against COVID-19 and receive a booster shot ahead of the upcoming spring semester.

Meanwhile, officials at Cornell University in Ithaca, New York, announced Tuesday that they have moved the campus into a "level red" alert after identifying evidence of suspected cases of the omicron variant in a "significant" number of the school's COVID-19 positive samples from students.

According to data from the Centers for Disease Control and Prevention, the omicron variant is estimated to account for more than 13% of newly confirmed COVID-19 cases in the New York and New Jersey area -- the highest proportion of any region of the United States.

-ABC News' Chris Donato and Arielle Mitropoulos