Dr. Anthony Fauci stressed Wednesday that the speed of vaccine development “was not compromising safety, nor was it compromising scientific integrity.”

"The speed is really a reflection of the extraordinary scientific advances that have been made that allowed us to do things in weeks to months that normally would have taken several years," Fauci explained at the Johns Hopkins Bloomberg School of Public Health Summit. "The process that went into deciding the safety and efficacy was both independent and transparent."

"We've got to be doing a lot of community engagement and community outreach to get people to understand," Fauci said.

ABC News' Sophie Tatum contributed to this report.

An 83-year-old passenger on board Royal Caribbean International’s Quantum of the Seas tested positive for COVID-19 on Wednesday, Singapore's Ministry of Health said in a statement.

The passenger had reported to the ship medical center with symptoms and was tested with PCR equipment on board. The 83-year-old was immediately isolated after getting the results.

Close contacts of the individual have tested negative and have been quarantined.

Singapore's National Public Health Laboratory will re-test that sample and a second sample will be taken to verify the results.

An epidemiological investigation has been initiated and contact tracing is in progress, the Ministry of Health said. All passengers will undergo mandatory COVID-19 testing before they are allowed to leave the terminal at Marina Bay Cruise Centre.

The ship will go through a "deep cleaning and disinfection," the cruise line said in a statement.

"The health and safety of our guests and crew are of utmost importance to us, and we have made the decision to cancel the 4-night cruise departing tomorrow, December 10," Royal Caribbean said.

ABC News' Christine Theodorou contributed to this report.

Authorities in the U.K. were investigating reports of two allergic reactions to the coronavirus vaccine from Pfizer/BioNTech -- a day after the country started its historic inoculation program.

Dr. June Raine, head of the UK regulatory body Medicines and Healthcare products Regulatory Agency (MHRA), said the agency was looking at two reports of allergic reactions to the vaccine, which rolled out yesterday.

"We know from the very extensive clinical trials that this wasn’t a feature but if we need to strengthen our advice... we get that advice to the field immediately,” said Raine.

The vaccine is believed to be both safe and 95% effective, according to Pfizer/BioNTech. The U.S. Food and Drug Administration was set to hold a hearing for emergency use of the drug on Thursday.

“There have been two cases of anaphylactoid reactions in individuals with a strong past history of allergic reactions both of whom carried an adrenaline auto injector,” the National Health Service (NHS) said in a statement on Wednesday. “These individuals developed symptoms of anaphylactoid reaction shortly after receiving the vaccine. Both recovered after appropriate treatment. We are seeking further information and will issue further advice following investigation.”

Pfizer/BioNTech have not yet commented on these latest findings.

Professor Stephen Powis, national Medical Director for the NHS, said: “As is common with new vaccines the MHRA have advised on a precautionary basis that people with a significant history of allergic reactions do not receive this vaccination after two people with a history of significant allergic reactions responded adversely yesterday. Both are recovering well.”

Russia registered 26,190 new coronavirus infections and 559 fatalities linked with the virus over the past 24 hours, officials said on Wednesday.

In Moscow, 5,145 new infections and 75 fatalities have been confirmed over the same time, according to official information.

The all-time high of 29,000 new cases was registered just last weekend but since then the number has been declining.

Since the start of the pandemic, Russia has confirmed 2,541,199 coronavirus infections and 44,718 deaths, officials have said.

ABC News' Alina Lobzina contributed to this report.

There were 192,299 new cases of COVID-19 confirmed in the United States on Monday, according to a real-time count kept by Johns Hopkins University.

It's the 35th straight day that the U.S. has reported over 100,000 newly diagnosed infections. Monday's tally is less than the country's all-time high of 227,885 new cases confirmed on Dec. 4, according to Johns Hopkins data.

An additional 1,404 deaths from the disease were also registered nationwide on Monday, down from a peak of 2,879 fatalities on Dec. 3, according to Johns Hopkins data.

COVID-19 data may be skewed due to possible lags in reporting over Thanksgiving followed by a potentially very large backlog from the holiday.

A total of 14,954,331 people in the U.S. have been diagnosed with COVID-19 since the pandemic began, and at least 283,746 of them have died, according to Johns Hopkins data. The cases include people from all 50 U.S. states, Washington, D.C., and other U.S. territories as well as repatriated citizens.

Much of the country was under lockdown by the end of March as the first wave of pandemic hit. By May 20, all U.S. states had begun lifting stay-at-home orders and other restrictions put in place to curb the spread of the novel coronavirus. The day-to-day increase in the country's cases then hovered around 20,000 for a couple of weeks before shooting back up over the summer.

The numbers lingered around 40,000 to 50,000 from mid-August through early October before surging again to record levels, crossing 100,000 for the first time on Nov. 4 and reaching 200,000 for the first time on Nov. 27.