The unvaccinated US teacher who infected 12 students with Covid: Lessons to be learned for the return to school

The powerful delta variant of the coronavirus, first detected in India nine months ago and now the predominant strain across the world, has changed the face of the enemy and transformed the war against the pandemic.

Delta is almost twice as contagious as previous strains of the virus, as illustrated by the best-analyzed school outbreak to date at Our Lady of Loretto Catholic School in Novato, in the US state of California. There, on May 19 of this year, an unvaccinated teacher with Covid-19 symptoms continued to teach, even removing her mask from time to time to read aloud to the children. Within a week, half of her 24 students had tested positive, even though the windows were open, the children were wearing masks and there was an air purifier in the classroom. Delta doesn’t allow for any margin of error.

Epidemiologist Tracy Lam-Hine, who led the study of the Covid-19 outbreak at Our Lady of Loretto, believes the case is a wake-up call as many countries get their children back to school after the summer vacation. “The most important lesson is that we cannot rely on just one layer of protection or even two. We have to use all the prevention strategies at once,” says Lam-Hine from the Marin County Health Department.

The Spanish Association of Pediatrics has had to revise its own back-to-school recommendations in light of the “invasion” of the delta variant, whose viral load in those infected is up to a thousand times greater than that of previous strains, according to a preliminary study in China. If a positive case infected an average of two or three people at the beginning of the pandemic, they can now infect five, which is higher than the flu. Spanish pediatricians have called for masks to remain mandatory for all children over six, even during outdoor recreation.

The fear is that the population’s youngest children could become a reservoir of the virus. Ninety-three percent of people aged over 40 in Spain have been vaccinated, but only 55% of children over 12 have received both doses, as María José Mellado, head of pediatrics at La Paz hospital in Madrid, points out. There are still no authorized vaccines for children under 12, which means that no one in this age bracket has been vaccinated so far. “It is clear that, at present, the population most susceptible to infection is children under 12 as well as older children who have not yet completed the vaccination schedule,” adds Mellado, who was also president of the Spanish Pediatric Association until last June.

The 14-day cumulative incidence among adolescents in Spain is still vertiginous, with 193 cases per 100,000 inhabitants – more than double the incidence among 60 year olds. However, a coronavirus infection in the very young is usually asymptomatic or very mild. The data is relatively reassuring. Since June 20, there have been almost 315,000 cases in children under 19 in Spain, with 1,900 hospitalized (0.6%), 91 admitted to intensive care units (ICUs) (0.03%) and seven deaths (0.002%), according to the National Epidemiology Center. Covid-19 can affect healthy children, but is predominantly a risk for those with existing health conditions and for unvaccinated adult family members.

The Spanish Association of Pediatrics is disappointed by the Health and Education ministries’ decision to reduce the minimum distance between students from 1.5 meters to 1.2 meters, “which will mean more children per class.” At the Our Lady of Loretto School, distance was key to stemming transmission. The children infected by the teacher were mainly those closest to her, as shown by the comprehensive analysis of the outbreak, published on the website of the US Centers for Disease Control and Prevention.

Bassat is calling on all school staff to get vaccinated as soon as possible if they have not already done so. The percentage of vaccinated teachers in Spain is very high, as suggested by data from the autonomous regions that have provided figures to EL PAÍS – 95% in Extremadura, 94% in Aragon and 92% in Catalonia – but there are still thousands who have not been inoculated, like the elementary teacher at Our Lady of Loretto in the US.

Bassat believes that, in order to relax the measures, the 14-day cumulative incidence should be below 25 cases per 100,000, with no notable outbreaks. Currently, the incidence stands at 131 cases per 100,000, with outbreaks across the country. Bassat would start by easing precautionary measures such as staggered entry into classrooms, lunchtime shifts, “obsessive hand hygiene with gel” and the ban on parents in school grounds. However, he would maintain mask-wearing indoors until vaccination coverage is even higher and the cumulative incidence is “very, very low – certainly fewer than 25 cases per 100,000.”

Of his own nine-year-old twins, Bassat says: “I will vaccinate them as soon as I can.” Data show that Pfizer’s vaccine – the first to be licensed for use in the very young – is highly effective in preventing serious cases in the 12 and over demographic. Hospitalization rates for Covid-19 are 10 times higher among unvaccinated adolescents, according to the latest report from the US Centers for Disease Control and Prevention.

Pfizer is now testing its vaccine on 4,500 children aged between six months and 11 years in Spain, the US, Finland and Poland, and plans to seek authorization for its use in the coming weeks. Other companies, such as Moderna and AstraZeneca, are also testing the efficacy of their vaccines on children. Some mathematical models estimate that herd immunity to the delta variant will be achieved when 85% of citizens are vaccinated, but children and adolescents under 15 account for more than 25% of the world’s population. Vaccinating them could be essential to ending the pandemic.

*Case investigators are not detailing the gender of the person who was the source of the outbreak for privacy reasons, but national and local media in the US have reported that it was a female teacher.

English version by Heather Galloway.