PFE Pfizer Inc

By WSJ Noted. 

The Covid-19 vaccines authorized in the U.S. are approximately 95% effective at preventing people from getting sick with symptoms, according to Pfizer and Moderna, the companies that produce them. But scientists are still studying whether vaccination prevents transmission to others.

KEY TAKEAWAYS

1. There is not enough evidence yet on whether the vaccines prevent asymptomatic infection.

Some research suggests that, without vaccines, roughly a quarter of Covid-19 transmissions result from asymptomatic spread. There is some indication that vaccination may reduce asymptomatic infection, resulting in reduced transmission. Preliminary evidence from Moderna showed that participants in a clinical trial who received the vaccine and were tested for Covid between their first and second doses had a roughly two-thirds reduction in asymptomatic infections. But experts note the data set was small and more results are needed.

2. Precautions will be necessary until the U.S. gets closer to herd immunity, experts say.

Wearing masks, social distancing and avoiding crowded spaces are likely to be necessary for some time, experts say. Marion Pepper, an immunologist and associate professor at the University of Washington in Seattle says that even after getting vaccinated, if someone is exposed to the virus it can take the body's immune response some time to control an infection and the potential for transmission depends on how quickly the infection is controlled. "Most vaccines prevent disease as opposed to preventing infection," says Anna Durbin, a professor of international health at Johns Hopkins Bloomberg School of Public Health who is working on the AstraZeneca Covid-19 vaccine trial and previously worked on the Pfizer vaccine trial. She believes Covid vaccine studies will eventually show a reduction in asymptomatic transmission but not a complete elimination.

3. Reaching herd immunity is partly dependent on enough people opting to be vaccinated.

Herd immunity is the point at which enough people are immune to a disease to make its spread unlikely. Roughly 75% to 80% of the U.S. population needs to be immune to Covid-19 to reach herd immunity, some studies estimate. But that number is a moving target and could rise as new variants emerge. Even if vaccines don't prevent transmission completely, they can still help populations achieve herd immunity if enough people take them, says Arnold Monto, an epidemiology professor at the University of Michigan School of Public Health who chairs the U.S. Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee. "Until we have broad-based vaccination and herd immunity, we should appreciate that it's possible to still get exposed to the virus really from anybody whether they're vaccinated or not," says John R. Mascola, director of the federal National Institute of Allergy and Infectious Diseases' Vaccine Research Center. But if the vast majority of people get the vaccine, "some asymptomatic transmission is not going to have much of a public health implication," he says.

Read the original article by Sumathi Reddy here.

(END) Dow Jones Newswires

January 18, 2021 12:26 ET (17:26 GMT)

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