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COVID-19 vaccines still not known to stop transmission

Photo from the Presidential Communications Operations Office

COVID-19 vaccines currently being rolled out in different countries are not yet known to prevent the transmission of the virus SARS-CoV-2, contrary to a statement of presidential spokesperson Harry Roque that vaccination will reduce the number of virus carriers.

Asked about an allegation by civic leader Teresita Ang See that around 100,000 Chinese nationals working for Philippine Offshore Gaming Operators (POGOs) have been inoculated, Roque said the information, if true, was welcome because it means there would be 100,000 fewer possible carriers of the coronavirus. He said:

Wala po akong impormasyon. Kung totoo man, eh ‘di Mabuti (I don’t know. But if it’s true, then good)! One hundred thousand less possible carriers of the COVID-19 virus

Clinical trials so far have found that the vaccines prevent symptomatic COVID-19 disease, including severe COVID-19, but not whether they could block viral transmission.

The Lancet Microbe said in a Dec. 18 editorial there are still “many unknowns” about the vaccines, including their ability to stop the virus from spreading:

Do any of the vaccines prevent viral transmission? Such data are only available from the ChAdOx1 nCoV-19 vaccine trial, but it was underpowered to generate firm conclusions…The unknowns of how the vaccine affects transmission makes the possibility of achieving herd immunity through vaccination uncertain.

The ChAdOx1 nCoV-19 vaccine was developed by the University of Oxford and AstraZeneca.

Researchers have pointed out the lack of public data on the safety and efficacy of the vaccine from China’s Sinopharm and the lack of official assessments of Sputnik V from Russia's Gamaleya Research Institute.

On Pfizer/BioNTech’s and Moderna’s vaccines, Harvard Health Publishing observed that the clinical trials did not measure whether a vaccinated person was less likely to infect others. It said:

Will the COVID vaccine prevent me from infecting others? The answer is, we don't know. It's possible that the vaccines protect against COVID-19 disease by preventing a person from becoming infected in the first place. However, it's also possible that the vaccine protects a person from COVID-19 illness, but does not prevent a person from becoming infected. In other words, a vaccinated person may have replicating virus in their nose and throat even if they are protected from becoming sick.

Citing the “limited information” on how much the COVID-19 vaccines may reduce transmission and how long protection lasts, the U.S. Centers for Disease Control and Prevention has urged vaccinated persons to still wear a mask, stay at least 6 feet away from others, avoid crowds, wash hands often and follow other guidance to protect themselves and others.

Said Harvard Health Publishing:

The bottom line? If you're among the first groups of people to get vaccinated, it's best to continue wearing masks and maintaining physical distance in order to protect others who haven't yet gotten the vaccine.

Reports that POGO workers had been vaccinated against COVID-19 vaccine came on the heels of President Rodrigo Duterte's disclosure that members of the Presidential Security Group had received the vaccine, which has not been approved by the Food and Drug Administration.

The Food and Drug Administration Act of 2009 prohibits the "manufacture, importation, exportation, sale, offering for sale, distribution, transfer, non-consumer use, promotion, advertising, or sponsorship of any health product that is adulterated, unregistered or misbranded."

Offenders face imprisonment of up to 10 years and a fine of up to P500,000, and up to P5 million for manufacturers, importers or distributors.


Centers for Disease Control and Prevention. (2020, December 30). Interim clinical considerations for use of mRNA COVID-19 vaccines currently authorized in the United States. Retrieved from

Corey, L. (2020, November 16). The messenger RNA vaccines and masks. Retrieved from

COVID-19 vaccines: The pandemic will not end overnight. (2020, December 18). The Lancet Microbe. doi: 10.1016/S2666-5247(20)30226-3

Food and Drug Administration (FDA) Act of 2009. Retrieved from

Harvard Health Publishing. (2020, December 28). Preventing the spread of the coronavirus.

Johns Hopkins Medicine. (n.d.) COVID-19 vaccine: What you need to know. Retrieved from

Press Briefing of Presidential Spokesperson Harry Roque. (2021, January 4). Retrieved from

Russell, S. (2020, December 16). Vaccines stop COVID-19 symptoms, but do they stop transmission? Retrieved from


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