New research casts doubt on the idea that prior infections with garden-variety coronaviruses might shield some people, particularly children, amid the pandemic.
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Let’s begin by defining our terms. Herd immunity is the hazy, long-promised end of the pandemic, but its requirements are quite specific. Jennie Lavine, a biologist at Emory University, likens it to wet logs in a campfire. If there’s enough water in the logs if there’s enough immunity in a population “you can’t get the fire to start, period,” she says. To be more technical about it, a population reaches herd immunity when the average number of people infected by a single sick person falls below one. Patient zero might infect another person, but that second person can’t infect a third. This is what happens with measles, polio, and several other diseases for which vaccines have achieved herd immunity in the United States. A case might land here, but the spark never finds much dry fuel. The outbreak never sustains itself.
The outlook seemed almost rosy when Dr. Joshua Schiffer and his colleagues set out to determine how factors like vaccination rate, vaccine effectiveness and social distancing might combine to bring the novel coronavirus pandemic under control.