US Life Expectancy Drops~~ What Is Heard Immunity?

AP 

PHOTO/MARK LENNIHAN

by AP

US life expectancy drops a year in pandemic, most since WWII; How will we know we've reached 'herd immunity?' 

 

Life expectancy in the United States has dropped a staggering one year during the first half of 2020 as the pandemic caused its first surge of deaths, health officials say.

 

Minorities suffered the biggest impact, with Black Americans losing nearly three years and Hispanics nearly two years, according to preliminary estimates from the Centers for Disease Control and Prevention, Marilynn Marchione reports.

 

“This is a huge decline,” the CDC said. “You have to go back to World War II, the 1940s, to find a decline like this.”  

 

Other health experts say it shows the profound impact of COVID-19, not just on deaths directly due to infection but also from heart disease, cancer and other conditions.

  

 

How will we know we've reached herd immunity? 

Here’s what’s known about the virus and herd immunity.

HOW IS THE HERD IMMUNITY THRESHOLD CALCUATED?

It’s a formula based on how contagious a virus is — or how many people catch the virus from one infected person, on average.

But the calculation offers only a broad target for when there might be a big drop off in spread. The figure could also vary by region.

“It’s not 64.9 is terrible and 70.1 is fantastic,” said Dr. Walter Orenstein, an infectious disease expert at Emory University.

Orenstein notes vaccination levels and other factors that affect spread could differ even within a city. 

HOW DO WE KNOW WE’VE REACHED HERD IMMUNITY?

Proof that we’re nearing herd immunity would be a “disruption in the chain of transmission,” said Ashley St. John, who studies immune systems at Duke-NUS Medical School at Singapore.

But don’t wait for any big declaration that we’ve reached that milestone.

To determine whether to relax restrictions, health officials will be watching infection and hospitalization trends as vaccinations roll out. And those decisions are likely to begin long before the ideal herd immunity threshold is reached, though they will be gradual and vary by region.

In India, for instance, scientists believe that more people will need to be protected in densely populated cities, where the virus spreads faster, than in its vast countryside.

India plans to look for antibodies in people nationally to figure out what percentage of its nearly 1.4 billion people have already been infected, said Dr. Jayaprakash Muliyil, who is advising the government on virus surveillance. 

Vaccine effectiveness also plays a role. Fewer people need to be vaccinated to achieve herd immunity if the shots have higher efficacy.

HOW DO CORONAVIRUS VARIANTS AFFECT HERD IMMUNITY?

It depends on the protection that past infection or vaccination gives you from the variant.

If vaccines were to prove notably less effective against a variant, it would require vaccinating an even greater portion of the population or updating existing vaccines to make them more effective, Orenstein said.

So far, it appears the shots provide at least some protection from the most worrisome variants. But scientists are still studying the situation, and worry about further mutations.

The variants have underscored the importance of vaccinating people as quickly as possible. Slowing transmission is critical since viruses can mutate when they infect people 

Health officials around the world are racing to vaccinate people — but what qualifies as “enough” is still an open question. The goal is to get to “herd immunity,” when enough people are protected from a virus, either from vaccination or a past infection. That makes it hard for the virus to jump from person to person. Many experts say at least 70% of a population needs to be protected. Candice Choi and Aniruddha Ghosal report. 

 

More from Around the World: 

• South African President Cyril Ramaphosa was among the first in his country to receive a vaccination, effectively joining an observational study as the Johnson & Johnson vaccine is not yet authorized for general use anywhere in the world.
• The European Union, under heavy pressure to ramp up vaccination efforts, approved contracts for 300 million additional doses of Moderna's vaccine and 200 million more from Pfizer. The EU is also funding more research to successfully hunt down variants and counter them.
• U.N. Secretary-General Antonio Guterres sharply criticized the “wildly uneven and unfair” distribution of vaccines, saying 10 countries have administered 75% of vaccinations.
• Pope Francis presided over a pandemic Ash Wednesday service, with reduced participation of the faithful and a revised rite to reduce the chances of infection as the virus keeps spreading through Italy.
• Dutch lawmakers are set to debate hastily drawn up legislation underpinning the country’s coronavirus curfew after a judge ordered it scrapped earlier this week.