Happy Friday! I am sure many may have read the news or heard on TV this week that Dallas County has officially reached "herd immunity" against COVID19. The Parkland Center for Clinical Innovation CEO in a statement mentioned that the county reached 80% herd immunity threshold on July 4, counting 46.6% being fully vaccinated and 48.7% of population with natural immunity having fully recovered for COVID19 infection.
Does it mean no one else within the Dallas county are likely to get infected with COVID19? What are the implications for our children under 12 years who cannot currently be vaccinated? Let's see…
First, what is herd immunity? Simply put, when the majority of population is immune to an infection, then this population ("herd"), by reducing the likelihood of person-to-person spread of infection, indirectly protects the vulnerable from catching the infection. So, individuals who are unvaccinated (such as newborns and those with medical reasons who cannot get vaccinated) get some protection as the disease does not have enough opportunity to spread within the community. The first usage of the phrase is attributed to Kansas veterinarian George Potter in the context of spontaneous abortions in livestock; but truly the first usage of the phrase "herd immunity" in the context of infection was in the 1923 publication in the Journal of Hygiene that referred to the phenomenon where experimental epidemic in mice stops with rising immunity in its population and with less number of susceptible animals in the colony. Indeed the term was popularized by the World Health Organization (WHO) during its campaign to eradicate smallpox. But then, with COVID19 and talking heads, "herd immunity" is no longer an unknown phrase!
Ok, back to Dallas County reaching the 80% herd immunity through a combination of natural infection and vaccination. While this is welcome news for us as a community, the leaders are also sounding caution. Why? Because SARS-COV2 is still around infecting people and the 80% number is not across the board for all zipcodes. There are ever newer variants that potentially spread more easily. There are still many who are unvaccinated. And the last word on the strength and persistence of natural immunity from COVID infection has not been said. How strong and how long lasting natural immunity after a COVID infection is is an area of intense scientific investigation. The current understanding is that generally those who experienced moderate to severe Covid-19 may have a more robust immune response compared to a more variable response in those who experienced mild infection.
Are our children protected because the county attained herd immunity? Now that is difficult to say, and from a conservative position, I would opine more likely not than otherwise. A modicum of protection is likely if the virus does not spread in the community, but for that we need more data points that consistently show low disease prevalence. We should also hope that all these efforts are not upended by increased transmission of variants that can evade our immune mechanisms. Finally, it is unavoidable that the burden of illness is likely to move from the older to the younger as more and more adults get vaccinated. A recent report from Israel (where they systematically vaccinated their population including more than 80% of adults) found that more than 50% of new COVID19 cases are being reported in children under the age of 19 years.
So children remain vulnerable to COVID unless we as a community protect them by using mitigation methods around them. While the risk is clearly low for vaccinated children without masks, for the younger ones who are not yet eligible for the vaccine, a mix of masks and social distancing can surely help. Indeed CDC has today posted updated Guidance for COVID-19 Prevention in Kindergarten (K)-12 Schools. Check the website for the full details, but I have copy-pasted their key takeaways below:
- Students benefit from in-person learning, and safely returning to in-person instruction in the fall 2021 is a priority.
- Vaccination is currently the leading public health prevention strategy to end the COVID-19 pandemic. Promoting vaccination can help schools safely return to in-person learning as well as extracurricular activities and sports.
- Masks should be worn indoors by all individuals (age 2 and older) who are not fully vaccinated. Consistent and correct mask use by people who are not fully vaccinated is especially important indoors and in crowded settings, when physical distancing cannot be maintained.
- CDC recommends schools maintain at least 3 feet of physical distance between students within classrooms, combined with indoor mask wearing by people who are not fully vaccinated, to reduce transmission risk. When it is not possible to maintain a physical distance of at least 3 feet, it is especially important to layer multiple other prevention strategies, such as indoor masking.
- Screening testing, ventilation, handwashing and respiratory etiquette, staying home when sick and getting tested, contact tracing in combination with quarantine and isolation, and cleaning and disinfection are also important layers of prevention to keep schools safe.
- Students, teachers, and staff should stay home when they have signs of any infectious illness and be referred to their healthcare provider for testing and care.
- Many schools serve children under the age of 12 who are not eligible for vaccination at this time. Therefore, this guidance emphasizes implementing layered prevention strategies to protect people who are not fully vaccinated, including students, teachers, staff, and other members of their households.
- COVID-19 prevention strategies remain critical to protect people, including students, teachers, and staff, who are not fully vaccinated, especially in areas of moderate-to-high community transmission levels.
- Localities should monitor community transmission, vaccination coverage, screening testing, and occurrence of outbreaks to guide decisions on the level of layered prevention strategies.
Bottom line: As it remains, COVID19 continues to spread, from one variant to another. Get vaccinated, socially distance, keep masks handy and cover yourselves if not vaccinated (or even if vaccinated and you are in an at-risk environment).
Have a great weekend!
Dr. Vani