Too Soon To Say How Long Survivors Stay Immune To COVID-19, Says WHO; New Study Strengthens Link Between Air Pollution & COVID-19 Deaths
SARS-CoV-2 (green) attacking a human cell (red)

It is still too early to tell how long immunity to SARS-CoV-2, the virus that causes COVID-19, may last after infection, the World Health Organization’s Technical Lead for COVID-19, Maria Van Kerkhove said at Monday press briefing.

Van Kerkhove’s comments came just after the publication of a new study by researchers from Kings College, London, which found that immunity seemed to peak at three weeks after symptoms first appeared, but then waned rapidly afterward.  Previous studies have also suggested that immunity to SARS-CoV-2 may wane within a few months after infection.

“We do expect that people who are infected with SARS-CoV-2, they do mount some level of an immune response…What we don’t know is how strong that protection is and for how long that protection will last,” said Van Kerkhove. 

While not referring specifically to the recent study, Van Kerkhove added that experience with other coronaviruses indicates that it is possible to become reinfected, and  there is data suggesting that immunity to SARS-CoV-2 could wane: 

“From our experience with MERS and SARS1, the virus that spilled over in 2003, we know that people can have an antibody response for maybe a year or even longer. But with the human coronaviruses that circulate regularly, it’s much shorter than that. So it’s an incomplete answer because we don’t have that answer yet,” said Van Kerkhove.

In the antibody study posted on the preprint server MedRxiv, researchers from King’s College London found that levels of neutralizing antibodies, the type of antibodies that can bind to and neutralize the virus, peaked at three weeks after symptoms appeared. 

However, immunity rapidly waned after the three-week mark. 

“Using sequential samples from SARS-CoV-2 infected individuals collected up to 94 days post-onset of symptoms, we demonstrate declining neutralizing antibody titres [levels] in the majority of individuals,” the authors, a group of researchers from Katie Doore’s lab at Kings College London, wrote. 

Those who survived more severe infection had higher levels of neutralizing antibodies at the three week mark. However the time it took for antibody responses to peak was consistent across all study subjects despite differing levels of disease severity.

The study, Longitudinal evaluation and decline of antibody responses in SARS-CoV-2 infection, measured antibody levels between March and June in 96 healthcare workers and patients who had laboratory confirmed cases of COVID-19.

Such studies casts further doubt over the potential of populations to develop broad “herd immunity” to the virus, no matter how widely it circulates, in the absence of a vaccine.  It may also prove to be a complicating factor in vaccine research, insofar as a potential vaccine would need to provoke a more long-lasting response to the virus in order to be a viable candidate for distribution on a global scale.

Dutch Study Finds Strong Link Between Air Pollution & More COVID-19 Deaths

A pig pokes his head out of a barn in Oosterhout, North Brabant, The Netherlands – where air pollution produced by livestock in rural areas is linked to higher rates of COVID-19 deaths.

Meanwhile, a Dutch study has yielded what some observers say may be the best study yet linking higher air pollution levels to higher rates of COVID-19 hospitalizations and deaths.

The peer-reviewed Dutch study is particularly noteworthy because it found the correlations in Dutch rural areas, which have some of the country’s highest air pollution levels – due to ammonia particulate emissions produced by livestock waste as well as farm fertilizers.

The Dutch study thus tends to strengthen the emerging evidence about a direct linkage between air pollution and COVID-19 outcomes. While a correlation between higher air pollution levels and higher COVID-19 death rates was previously identified in two previous studies by a group of researchers at Harvard’s School of Public Health, as well as researchers in Italy, critics had said that those findings might be due to other factors related to the urban environment, such as poverty or other health inequalities – and not directly linked to air pollution exposures per se.  

The Harvard study looked county-wide throughout the United States and found an 8% increase in coronavirus deaths for a single-unit rise in fine particle pollution, while controlling for factors such as obesity and smoking incidence. 

However, the Dutch study analyzed data at the municipal level for some 355 Dutch municipalities, averaging 95 km2 in size, as compared to the US county level, which is over 30 times larger.

This means that researchers could look more granularly at pollution exposures and outcomes, said lead author Matt Cole, in a blog in the journal The Conversation. The Dutch study also uses COVID-19 data up to 5 June 2020, allowing it to capture almost the full wave of the epidemic.

“The correlation we found between exposure to air pollution and COVID-19 is not simply a result of disease cases being clustered in large cities where pollution may be higher,” Cole said. “After all, COVID-19 hotspots in the Netherlands were in relatively rural regions.”

COVID-19 cases per 100,000 people and annual concentrations of PM2.5 (averaged over the period 2015-19) in the Netherlands. (Matt Cole, The Conversation)

The study found the highest air pollution concentrations included rural areas in the south-eastern provinces of North Brabant and Limburg, where intensive pig and chicken production produces large amounts of ammonia particles as a byproduct of livestock excrement, which form a significant proportion of fine particulate matter in air pollution. COVID-19 hospitalization and death rates were similarly clustered in those same regions.

The Dutch study found that an increase in fine particulate matter concentrations of 1 microgram per cubic metre was linked with an increase of up to 15 COVID-19 cases, four hospital admissions and three deaths, on average.

While media reports had suggested that some of the excess deaths seen in that region of The Netherlands may have also been due to the mass gatherings in rural areas for carnival season in February and March, the researchers controlled statistically for those gatherings as well as other factors.

“The relationship we found between pollution and COVID-19 exists even after controlling for other contributing factors, such as the carnival, age, health, income, population density and others” Cole observed.

The Dutch study, co-authored by Ceren Ozgen of the University of Birmingham and Eric Strobl of the University of Berne, is also the first study to have been accepted for publication in a peer reviewed journal – Environmental and Resource Economics.

Image Credits: NIAID/NIH, Flickr: Dutchairplaneshooter.