CDC shifts the pandemic goal from achieving herd immunity

From the early days of the pandemic, there was a common goal to end it: Achieve herd immunityAt that time, so many people were immune to the virus that the virus exhausted the potential hosts that could infect, leading to an outbreak.

Many Americans have accepted this new farming phrase, and the ensuing prediction is that once 70% to 80% or 85% of the population is vaccinated against COVID-19, the virus will disappear and the pandemic will end.

The flock is uneasy now. Experts from the Centers for Disease Control and Prevention have made herd immunity a national goal.

Prospects Achieve clear herd immunity goals Say “very complicated” Jefferson Jones, A medical officer of the CDC COVID-19 Epidemiology Working Group.

“Thinking that we will be able to reach a certain threshold so that the infection can no longer spread, it may not be possible,” Jones admitted to a member of the CDC team that provided vaccine recommendations last week.

Jones pointed out that vaccines are very effective in preventing COVID-19 cases that cause severe illness and death, but no vaccine has proven to be reliable in preventing the spread of the virus. Recent evidence also suggests that the immunity provided by the vaccine may weaken within a few months.

As a result, even if vaccination becomes widespread, the coronavirus may continue to spread.

He said, “We do not encourage” to think from the perspective of “strict goals.”

arrive Dr. Oliver Brooks, As a member of the CDC Immunization Practice Advisory Committee, this is thought-provoking new information with potentially worrying implications.

Brooks, chief medical officer of Watts Healthcare in Los Angeles, said that because only 58.5% of Americans are fully vaccinated, “we really need to increase” the COVID-19 vaccination rate. Unfortunately, he said, Jones’ accidental admission “almost left you with no motivation to get more people vaccinated.”

A man checks a woman's temperature with a forehead reader

Dr. Oliver Brooks (center) watching Lucy Arias check the patient’s temperature at the COVID-19 screening station outside the Watts Health Center in Los Angeles.

(Irfan Khan/Los Angeles Times)

Brooks said he fears that as the CDC removes specific herd immunity targets, this will lead to Efforts to improve the level of vaccination.

If public health officials stop talking about “groups,” people may ignore the fact that vaccination is not only an act of personal protection, but also a way of protecting the community.

The public’s commitment to herd immunity may also go further Undermine the credibility of the CDC In the fight against the coronavirus.

From the use of masks to how the virus spreads, the agency has made some dramatic changes during the pandemic. These reversals were triggered by new scientific discoveries about the behavior of the new virus, but they also provided sufficient support for COVID-19 skeptics, especially those in conservative media.

“it is Science communication issues,” said Dr. John Brooks, The chief medical officer of the CDC COVID-19 response.

“We said that based on our experience with other diseases, when you reach 70% to 80%, you usually get herd immunity,” he said.

A gray cat sits on a man's shoulder

The chief medical officer of CDC’s response to COVID-19, Dr. John Brooks, works with his cat, Cosmo, at home.

(CDC)

But the SARS-CoV-2 virus did not get a memo.

“It has a lot of skills, and it has repeatedly challenged us,” he said. “Until the herd immunity is reached, it is impossible to predict what the herd immunity in the new pathogen will be.”

CDC’s new approach will reflect this uncertainty. Public health officials did not specify a vaccination target that promised to end the pandemic, but wanted to redefine success in terms of new infections and deaths-they would speculate that herd immunity has been achieved when the two remain low for a period of time.

“We want clean, simple answers, and sometimes they do exist,” John Brooks said. “But at this point, we are still learning.”

Herd immunity has never been as simple as many Americans have imagined, saying Katherine Hall Jamison, Director of the Annenberg Center for Public Policy at the University of Pennsylvania, and an expert in communicating the challenges of science to increasingly suspicious—often conspiracy-minded—citizens.

This is an idea Appeared about a century ago From the field of animal husbandry medicine.Epidemiologists now use a standard to calculate it equationBut like many tools that use mathematics to simulate complex processes, it makes some simplified assumptions.

For example, it assumes that there is an unrealistic consistency in the behavior of individuals and groups and the ability of the virus to spread from person to person.

Therefore, it does not reflect the diversity of population density, living arrangements, transportation patterns, and social interactions that make Los Angeles County so different from Boise County, Idaho. This also does not explain the fact that Boise County (less than 35% of adults are fully vaccinated) cannot be protected from the 73% adult vaccination rate in Los Angeles County.

“Humans are not a group,” Jamison said.

She said that by formulating vaccination campaigns around the needs of “community immunization,” public health leaders will receive better services. She added that this will make people think in a more localized way-when it comes to a person’s risk of infection, those are what really matters.

Changes in the coronavirus itself have also made herd immunity a moving target.

The calculation that yields an estimate of 70% to 85% of herd immunity depends to a large extent on the congenital infectivity of SARS-CoV-2. However, with the emergence of new virus strains such as Alpha and Delta variants, the ability of the virus to spread from person to person has increased. Sharp escalation in the past year.

In addition, the herd immunity calculation assumes that when people gain immunity, they will maintain immunity for a known period of time.But obviously, whether it’s vaccination or natural infection Provide lasting protectionA booster or “breakthrough” case may occur, but how long it lasts is still unknown.

This is how science works, saying Raj Bhopal, A retired professor of public health at the University of Edinburgh, written The maddening complexity of herd immunity.

For any organization engaged in the transmission of public information, “it is difficult to communicate uncertainty and maintain authority,” Bhopal said. “Unfortunately, we cannot take the public along this uncertain path.”

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