along with Highly Infectious Delta Coronavirus Variant Spread at an alarming rate, The World Health Organization urged people in late June Wear masks indoors again-even for those who are fully vaccinated. On July 15, Los Angeles County, California announced that it would again require cover up In public indoor spaces, regardless of the vaccination status.This is being tracked By recommendation -Although not mandatory-Starting from the seven counties in the Bay Area, everyone again wears masks in public indoor environments.

It is worth noting that the US Centers for Disease Control and Prevention has not yet taken a similar position. July 12, National Federation of NursesThe nation’s largest professional association of registered nurses called on the CDC to reconsider the surge in new infections and hospitalizations across the country.The conversation asked Peter Chin-Hong, a Doctors specializing in infectious diseases At the University of California, San Francisco, help connect the science behind these seemingly mixed messages.

What is the scientific basis behind the WHO recommendations?

There is clear and growing evidence that– Although rare —— A breakthrough COVID-19 infection may occur, Even when fully vaccinated.Especially so New and worrying variants.

CDC has been watching these data closely. By mid-July, Nearly 60% of the U.S. population 18 years of age or older have been fully vaccinated. People who are fully vaccinated rarely get infections, and the serious consequences of COVID-19 in this population are even rarer—— Although they still happenHowever, the CDC stopped tracking asymptomatic non-hospital COVID-19 cases among fully vaccinated individuals on May 1.

However, vaccinated and unvaccinated people have very different risks of serious illness and death.

Are delta variants more likely to have breakthrough infections?

may be. Preliminary data suggests that an increase in variants such as Delta may increase the chance of breakthrough infection in people who received only the first dose of the vaccine.For example, a study that has not been peer-reviewed found that a single dose of Pfizer vaccine is only 34% opposed the Delta variant, while 51% Fight against older Alpha variants in preventing symptomatic diseases.

But for those who have been fully vaccinated, the data is even more reassuring.After two doses, Pfizer vaccine Still provide strong protection Based on real data from the Delta variant Scotland And various other countries; and in preliminary research Canada and UK, The researchers noticed that the effectiveness of symptomatic diseases is only “moderately” reduced Alpha variant is 93%, Delta variant is 88%.

However, a recent preliminary report from Israel is thought-provoking.Before the Delta variant became popular, from January to April, Israel reported that Pfizer vaccines are 97% effective in preventing symptomatic diseases. However, Since June 6According to preliminary data reported by the Israeli Ministry of Health in early July, as the Delta variant spreads more widely, the Pfizer vaccine is 64% effective in preventing symptomatic diseases.

And in another New report that has not yet been peer-reviewed, The researchers compared the serum antibodies of people vaccinated with Pfizer, Moderna and Johnson & Johnson, and found that the Johnson & Johnson vaccine can Much lower protection Compared with mRNA-based vaccines, it targets Delta, Beta and other variants. Therefore, the researchers suggest that Johnson & Johnson vaccine vaccinators will benefit from booster immunization, preferably using one of the mRNA vaccines.However, this is a limited laboratory study that does not investigate whether real people are sick or not, and are related to Peer-reviewed research The Johnson & Johnson vaccine was found to have a protective effect on the delta eight months after vaccination.

However, in all reports and studies, the vaccine against Delta variants is still very effective in preventing hospitalizations and serious diseases-arguably the result we care about most.

All these emerging data support WHO’s recommendation that even fully vaccinated people continue to wear masks.Most parts of the world still have Low vaccination rate, Use a Vaccine scope and Variable efficacy In preventing infection and Different burden The circulation of the SARS-CoV-2 virus. In this case, it makes sense for the WHO to give a conservative recommendation to cover up everyone.

Who is actually protected by the blocking recommendation?

The WHO recently called on people who have been vaccinated to continue to wear masks mainly to protect those who have not been vaccinated-including children under 12 years of age. Not yet qualified For vaccines in the United States, unvaccinated people have a much higher risk of infection and infection Spread SARS-CoV-2, And complications due to COVID-19.

And there is another People who are vaccinated have a low risk of infection, But this risk varies from region to region. In areas with high virus transmission rates, low vaccination rates, and high mutation transmission rates, vaccinated people are more likely to be infected than people living in areas with low levels of community virus.

Does the situation in the United States need to be covered up (again)?

I suspect that the CDC is unlikely to seek general US recommendations for wearing masks at this time.Take the whole National vaccination rate is high with one COVID-19 is generally low The burden of hospitalization and death, the COVID-19 situation in the United States and Most of the world.

Some experts are also worried that the official news is issued that people who are vaccinated should wear masks. May dissuade People who have not been vaccinated seek vaccines.

What changes indicate that it is time for the United States to cover up again?

There are emotional red flags, and then more realistic red flags, which may call for people who are fully vaccinated to wear masks indoors across the country.

More than 100 infections per 100,000 people per week is defined as “High” community spread, The worst category, by CDC. Take Los Angeles County as an example, Has surpassed That mark, and More than 10,000 coronavirus cases every week.

A more practical masking measure is the number of hospitalizations, because it is directly related to the use of medical resources.Some The researcher proposed A threshold Five COVID-19 cases – Average number of days – Every 100,000 people are hospitalized, which may be a more ominous sign than the infection rate. Los Angeles County also exceeds this point.

Depending on how many people are fully vaccinated in a region, the surge may be a regional phenomenon. As long as the number of hospitalizations and deaths remains controllable across the country, and hospital capacity remains unchanged, the entire United States may not need to wear masks indoors for full immunization.

Peter Zhanhong, Associate Dean of Regional Campus, University of California, San Francisco

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