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Governments and officials around the world hope that COVID-19 vaccines can create “herd immunity” to protect large populations.
Some experts predict that giving a vaccine to just two-thirds of the population could protect entire communities or nations. But the effectiveness of such efforts depends largely on what vaccines can prevent.
What is herd immunity?
Herd immunity occurs when a large percentage “of a community (the herd) becomes immune disease, making the spread of the disease from person to person unlikely. As a result, the entire community is protected, not just those who are immune, ”says the Mayo Clinic on its website.
But there are still many open questions about herd immunity and COVID-19 vaccines.
For example, will early vaccines be able to stop the spread of the virus or just keep people from getting sick? How many people in a population will accept a vaccine? Will vaccines offer the same protection to everyone?
Josep Jansa is an expert at the European Center for Disease Prevention and Control (ECDC) based in Stockholm.
“Herd immunity is sometimes wrongly understood as individual protection,” Jansa told the Reuters news agency. He added: “Collective immunity it means to the protection of the community, not to how an individual is protected. ”
R value and spread of disease
One of the central questions about herd immunity and COVID-19 is the reproduction rate, or R-value, of the virus that causes it. The R-value is a measure of how many people contract the virus from an average infected individual in settings where there are no restrictions. For example, an R value of 2 means that an infected person is expected to transmit the virus to 2 other people.
Winfried Pickl is a professor at the Medical University of Vienna.
“The problem is that for now we don’t know exactly how fast the virus spreads without precautions and with the normal travel and social activities that we had a year ago, ”Pickl told Reuters.
Health experts have pointed out that any vaccine less than 100% effectiveness it would require increased vaccines to achieve herd immunity. Early data on the major COVID-19 vaccines, from Pfizer-BioNTech and Moderna, suggest only 90 percent efficacy.
Amesh Adalja works at the Johns Hopkins Center for Health Security. He said a good target for immunity in the United States would be to vaccinate more than 70 percent of the population. But the number could increase if the vaccines are less effective, he added.
ECDC uses an estimated herd immunity level of 67 percent for its models. In Germany, Chancellor Angela Merkel said this month that COVID-19 restrictions could be lifted once 60 to 70 percent of the population achieve immunity.
Experts from the World Health Organization have also suggested a vaccine coverage rate of 65 to 70 percent as a way to achieve the immunity of the population through vaccination.
Vaccines and virus transmission
Experts say another important question is whether vaccines can stop the spread of the coronavirus, which causes the COVID-19 disease.
So far, the evidence suggests that the first COVID-19 vaccines will at least prevent people from developing the disease. But it cannot be ruled out that people still contract the virus and pass it on to other people.
Bodo Plachter is Professor and Deputy Director of the Institute of Virology at the University Hospital of the University of Mainz in Germany. Plachter said that respiratory Infections can be difficult to block completely with vaccines, although injections are expected to reduce the amount of virus circulating.
“It may well be that vaccinated people shed less viruses, “he said. “But it would be a mistake,” he added, to think that “vaccination alone can suppress a pandemic. ”
I am John Russell.
Kate Kelland and Ludwig Burger reported on this story for Reuters. John Russell adapted it to learn English. Bryan Lynn was the editor.
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Words in this story
immune – adj. have special protection from something; of or related to the body’s immune system
refer – v. talk or write about someone or something
caution – n. something that is done to avoid possible damage or problems in the future
effectiveness – n. the power to produce a desired result or effect
respiratory – adj. doctor: of or related to breathing or the organs of the body that are used to breathe
shed – v. Get rid of something); lose (leaves, skin, fur, etc.) naturally
suppress – v. to slow or stop the growth, development, or normal functioning of (something)
