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随着冠状病毒疫苗分布在全国各地,仍然存在一个大问题:尽管疫苗减少了症状性covid-19,可接种疫苗的个体仍然传递病毒?

The answer could significantly impact whether there is a fourth wave of coronavirus infections this spring, according to new models from the Fred Hutchinson Cancer Center. If the FDA-approved Pfizer and Moderna vaccines prevent transmission, that may have a big impact on virus spread.

Joshua Schiffer博士of the Fred Hutchinson Cancer Research Center. (Fred Hutch Photo)

“That would get us to herd immunity more quickly, prevent more cases and deaths, and prevent or severely limit a fourth wave of cases in the spring that would persist through the summer,” saidJoshua Schiffer博士, an infectious disease researcher at Fred Hutch. “It ends up amounting to huge differences in cases and deaths, and whether we’ll have to deal with this one more time in the spring and summer.”

Schiffer worked on a recently-released预印迹andits companion paperon this topic. While those findings haven’t been peer reviewed, outside observers such asDr. James Wood, a mathematician and professor who specializes in vaccine-preventable disease, said the studies offer interesting ideas on how to figure out whether the vaccines prevent transmission — findings that could help us better predict the pandemic’s path in 2021.

“主要的外卖留言是,尽管现代人等等,但研究,我们还不确定这些疫苗对传播的影响 - 并且可以存在社区级别的巨大变化,”木材说。

疫苗如何工作

Vaccines can prevent an exposed individual from developing symptoms of a disease. But whether that vaccine prevents an infection — and thereby stops the disease from spreading to others — presents a gap in the literature, Schiffer said.

There are some studies that offer optimism. For example,one study shows如果接种疫苗的孩子获得水痘,那么如果暴露于病毒,它们的可能性远不太可能感染未接触的家庭成员。

Similarly, other研究表明细菌感染的儿童疫苗接种的增加导致未接种疫苗的老年人的病例和死亡的减少,表明疫苗接种也会影响社区传播。

“Those studies are very suggestive that vaccines protect against transmission, but they aren’t a slam dunk,” Schiffer said.

如果疫苗没有完全停止传输,它仍然可以有效地减少社区传播,但需要更多的时间。

“You would still march toward herd immunity, but you just march more slowly,” Schiffer said.

建模的可能性在西雅图

Hutch researchers modeled the impact of vaccines that would stop transmission versus ones that would not in Seattle’s King County, which has a population of 2.25 million people. They also looked at what might happen absent any vaccine.

如果没有疫苗,而且没有当前社会疏远行为的变化,该县可能会在明年1月至7月期间看到高达5,900例,每天99人死亡。

The numbers improve dramatically with a vaccine, and even more if that vaccine prevents transmission.

A vaccine that reduces a vaccinated person’s symptoms but doesn’t stop them from transmitting a possible infection would prevent roughly 40% of infections and 60% of deaths during the vaccine roll out period, the Hutch models show. If the vaccine has both effects, though, it could prevent 70% of infections and 70% of deaths.

Other factors can play a role, such as the speed and size of the rollout. Those become increasingly important if the vaccine does not block transmission.

“If we roll out more slowly, the differences become accentuated,” Schiffer said. “This really matters: the speed of the rollout is the strongest variable we see.”

How people behave is significant, too. Physical distancing, masking and remote work all play into the impact and the severity of the next wave.

The role of asymptomatic transmission —which is still debatable— could also influence the vaccine’s impact, saidDr. Natalie Dean是,佛罗里达州大学才能参与弗雷德·赫格特学习。即使疫苗转化为无症状感染的所有症状感染,仍然可能会减少传播。

How can we find out?

One way to determine whether the COVID-19 vaccines also stop transmission is aHuman Challenge study,Hutch文件中描述的一个想法之一。这意味着服用年轻,健康的志愿者并用真正的疫苗或安慰剂注射它们。然后,研究人员将在检查病毒负荷之前故意将它们暴露于病毒,这是一种衡量人们在病毒上传递的可能性。

以前已经完成了这些研究some respiratory virusesandmalaria, Schiffer said. But there are some ethical concerns. People enrolled in that study could develop the disease themselves and risk their own wellbeing and would have to be followed very closely.

Another idea is to enroll young healthy people on a university campus, inject them with either the true vaccine or a placebo, then monitor them often to check for the presence of virus and whether they develop symptoms. Sincecollege campuses have shown substantial COVID-19 transmission, it’s likely many will be exposed to the virus naturally. While the frequent testing would be a massive undertaking, the environment would capture a real-world situation.

“这些研究中的任何一个都可能是重要的并且可以相互补充,”Schiffer说。

Schiffer said he’s hopeful that studies measuring transmission among individuals who have received the Moderna and Pfizer vaccines will be rapidly conceived and performed. Those results would be critical for policy makers, informing them whether herd immunity has been reached in early spring, “which will in turn help predict whether it is safe to slowly reopen society,” Schiffer said.

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