With the highly infectious variant of the delta coronavirus spreading at an alarming rate, the World Health Organization urged people in late June 2021 to wear masks indoors again – even those who are fully vaccinated. And on July 15, Los Angeles County, Calif., Announced it would once again require masking in public indoor spaces, regardless of vaccination status. This was followed by a recommendation – but not a mandate – from seven Bay Area counties for all to re-donate masks in indoor public places.
Notably, the U.S. Centers for Disease Control and Prevention has yet to take a similar position. On July 12, National Nurses United, the largest professional association of registered nurses in the country, called on the CDC to reconsider its decision in light of the increase in the number of new infections and hospitalizations across the country. The Conversation asked Peter Chin-Hong, an infectious disease physician at the University of California, San Francisco, to help put the science behind these seemingly mixed messages into context.
What is the science behind the WHO recommendation?
There is clear and growing evidence that – although rare – groundbreaking COVID-19 infections can occur, even in fully vaccinated people. This is especially true with the emerging variants of concern.
The CDC has been monitoring this data closely. As of mid-July 2021, nearly 60% of the U.S. population aged 18 or older had been fully immunized. Infections in those who are fully vaccinated are rare, and the serious consequences of COVID-19 in this population are even rarer – although they still occur. However, the CDC stopped tracking outpatient cases of COVID-19 for people with and without symptoms among those fully vaccinated on May 1, 2021.
The risk of infection leading to serious illness and death, however, differs markedly between vaccinated and unvaccinated people.
Are breakthrough infections more likely with the delta variant?
Perhaps. Preliminary data suggests that increasing variants like delta may increase the risk of major infections in people who only received their first dose of the vaccine. For example, a study not yet peer reviewed found that a single dose of Pfizer vaccine was only 34% effective against the delta variant, compared to 51% against the old alpha variant in terms of preventing symptomatic disease.
But the data is more reassuring for those who have been fully immunized. After two doses, the Pfizer vaccine still offers strong protection against the delta variant, according to actual data from Scotland and various other countries; and in preliminary studies in Canada and England, researchers noted only a “modest” decrease in efficacy against symptomatic disease from 93% for the alpha variant to 88% for the delta variant.
A recent preliminary report from Israel is sobering, however. Before the delta variant became mainstream, from January to April 2021, Israel reported that Pfizer’s vaccine was 97% effective in preventing symptomatic illnesses. However, as of June 6, with the delta variant circulating more widely, the Pfizer vaccine has been 64% effective in preventing symptomatic disease, according to preliminary data reported by Israel’s health ministry in early July.
And in another new report that has yet to be peer reviewed, the researchers compared the blood serum antibodies of people vaccinated with the Pfizer, Moderna and J&J vaccines and found that the J&J vaccine offered much weaker protection. versus delta, beta and other variants, compared to vaccine-based mRNA. As a result, the researchers suggest that recipients of the J&J vaccine would benefit from booster immunizations, ideally with one of the mRNA vaccines. However, this is a limited lab study that does not investigate whether real people got sick and contradicts a peer-reviewed study that found the J&J vaccine to protect against delta eight months after vaccination. .
In all reports and studies, however, the vaccine’s efficacy against the delta variant is consistently very high in preventing hospitalizations and serious illness – arguably the results that interest us the most.
All of this emerging data supports the WHO recommendation that even fully vaccinated people continue to wear masks. Most countries around the world still have low vaccination rates, use a range of vaccines with varying efficacy to prevent infection, and have different circulating loads of the SARS-CoV-2 virus. Against this background, it makes sense for the WHO to give a conservative recommendation to hide for all.
Who is actually protected by the masking recommendations?
The WHO’s latest call for fully vaccinated people to continue to wear masks is primarily aimed at protecting the unvaccinated – which includes children under 12 who are not yet eligible for vaccines in the United States. Unvaccinated people are at a significantly higher risk of becoming infected and transmitting SARS-CoV-2, and of developing complications from COVID-19.
And, again, there is always a low risk of infection for those vaccinated, but that risk differs by region. In areas with highly circulating virus and low vaccination rates, and with highly transmissible variants, the likelihood of infection is higher in vaccinated individuals than in people living in areas with low virus levels in the community.
Does the American situation (still) deserve to be masked?
I suspect the CDC is unlikely to pursue a universal US recommendation to wear masks at this time. With a high overall immunization rate nationwide and a low overall burden of COVID-19 hospitalization and death, the United States has a very different COVID-19 landscape than most countries in the world.
Some experts are also concerned that sending an official message stating that vaccinees should wear masks will deter unvaccinated people from getting the vaccine.
What changes would signal that it is time for the United States to go into hiding again?
There are emotional red flags and then there are more realistic red flags that can spark a nationwide call for indoor masking for fully vaccinated people.
Having more than 100 cases of infection per 100,000 people per week is defined as “high” community transmission, the worst category, by the CDC. Los Angeles County, for example, has already topped that mark, with more than 10,000 cases of coronavirus per week.
A more pragmatic measure of masking is the number of hospitalizations, as it is directly related to the use of health resources. Some researchers have proposed a threshold of five COVID-19 cases – averaged over several days – hospitalized per 100,000 people, which would potentially be a more worrying signal than infection rates. Los Angeles County has surpassed that as well.
Outbreaks are likely to be a regional phenomenon based on the number of fully vaccinated people in an area. As long as hospitalizations and deaths remain generally manageable nationally and hospital capacity is intact, the United States as a whole may not need to return to hiding indoors for people entirely. immune.[The Conversation’s most important coronavirus headlines, weekly in a science newsletter]