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.

On Friday, hospitals in Massachusetts will stop offering elective surgeries that can be safely postponed, Gov. Charlie Baker said at a press conference Monday afternoon.

"This action will free up unnecessary staffing and beds," Baker said. "We all know we're in the midst of a second surge. We're seeing a higher number of new cases each day. And in turn, an increase in hospitalizations statewide."

On Sunday, Massachusetts reported 4,747 new infections and a seven-day average testing positivity rate of 5.3%. There are 1,416 people currently hospitalized with COVID-19.

Despite the worsening statistics, the state is better prepared this time around, Baker insisted. In addition to reallocating hospitals resources, the state is ramping up and winterizing testing sites, stockpiling PPE and preparing two field hospitals in Worcester and Lowell.

-ABC News' Kelsey Walsh contributed to this report.