Viewpoint: Mu Variant Might Escape Immunity from Vaccines, Past Infection


After the Delta surge subsides, another surge is expected, possibly from the Mu variant. If Mu completely escapes immunity from vaccines and past infections, we must resort to stringent public health strategies.

Last week the United States witnessed continued devastation brought on by the Delta Variant and an inability to form a consensus on how to stop the spread of the virus. However, we also made enormous strides in understanding how the virus spreads and what is necessary to stop this pandemic.

Many have embraced mitigation strategies to bridge our society to a time when herd immunity could be reached through natural immunity or with the vaccines. Hopes for the success of this strategy were greatly diminished with the report from the Centers for Disease Control and

Kevin Kavanagh, MD

Kevin Kavanagh, MD

Prevention (CDC) which examined over 1 million blood donation specimens between July 2020 and May 2021, taken from a catchment area which covered 74% of the United States population. The researchers found SARS-COV-2 antibodies in 83.3% of specimens. Not captured were individuals who had an infection and then became seronegative but still were immune due to memory B cells. In addition, one would expect the percent positivity rate to be less in the beginning of the catchment period as compared to the end. Similar to the findings in Deli, India, and Manaus, Brazil, these high antibody rates were viewed by many as indicating the achievement of herd immunity. However, all of these countries, were crushed by a subsequent wave caused by an immune escape variant. A recent report from New Deli found 25% of 288 fully vaccinated health care workers developed a breakthrough infection. The severity of these infections was low and none required hospitalization.

The United States was then crushed with an immune-escape Delta variant with a major surge in August and continuing into the near future. As discussed in an Infection Control Today® article, another major immune escape variant is likely to occur. And the emergence of the Mu variant, B.1.621, may well fit the bill. On August 30, 2021, the World Health Organization (WHO) classified Mu as a variant of interest. The Mu variant started in South America and spread to Ecuador and other countries. The WHO reports its worldwide prevalence is decreasing but in Columbia it accounts for 39% of cases during their Delta surge. Thus, Mu appears to effectively compete with the Delta variant. In the United States, Mu has been detected in all but 1 state and there have been over 2000 cases.

It is also becoming apparent we cannot vaccinate our way out of this pandemic. The vaccine’s effectiveness is waning, and the variants are becoming resistant making the wearing of masks, in a mask resistant population, an imperative. It was welcome news to finally have a clinical trial published by research from Stanford which demonstrated the effectiveness of surgical masks in curtailing COVID-19 infections. The trial involved randomized villages in Bangladesh with more than 342,000 participants. Correct mask wearing was 13% in the control group and 42% in the intervention group. Despite suboptimal mask usage in the intervention group, seropositivity dropped 11.2%. In those over 60, there was a decrease of 34.7%.

Mask usage became even more important with a recent report in the CDC’s Morbidity and Morality Weekly Report (MMWR) demonstrating aerosolization in schools. A school outbreak was traced back to an unvaccinated, mildly symptomatic teacher who reportedly read unmasked to her 24 students who presumably were wearing masks. All students were unvaccinated because of age. All 5 students in the first row, closest to the teacher’s desk, acquired the virus. But 2 of the 4 students in the back row also acquired the virus. The attack rate in the first 2 rows was 80% and 25% in the back 3 rows. It is evident that the virus was aerosolized and stopping spread would require a distance much greater than 6 feet (let alone the 3 feet now recommended for school distancing). There were also another 8 cases identified in parents and siblings demonstrating that children at school can be significant vectors for spreading COVID-19.

The students also wore masks, illustrating that masking as a sole intervention is inadequate. Masks need to be upgraded to well-fitted medical grade, KN95 or N95 masks, along with testing of all students and staff twice weekly, and better school ventilation. Even with these strategies the virus may still be expected to cause outbreaks, necessitating the need for smaller class sizes, podding, hybrid classes and teleschooling.

Because of the high infectivity of current variants and their propensity for aerosolization, some airlines in Europe are now requiring medical grade masks or respirators.

The United States definitely needs to head in a new direction. The Delta surge exemplifies the need to maintain the highest level of immunity by becoming vaccinated, and if indicated, obtaining a booster. After the Delta surge subsides, another surge is expected, possibly from the Mu variant. If Mu completely escapes immunity from vaccines and past infections, we must resort to stringent public health strategies. Eventually, the United States may need to adopt an elimination strategy, sacrificing short-term for long-term societal benefits. But whatever strategy is adopted, all Americans must embrace public health measures, or we will not be successful in viral mutations and the pandemic.

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