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NEW THREAD: But one with a potentially small target audience, namely front-line #NHS staff of all stripes who have had SARS-CoV-2 infection at some point during the pandemic, and are heading into January.
Anyone else interested is a welcome bonus. ;)
Anyone else interested is a welcome bonus. ;)
This NEJM study is essential reading for front line health care workers (HCW) who have recovered after SARS-CoV-2 infection and aren’t sure what their risk of reinfection may be.
SPOILER: It’s not high. At all. https://www.nejm.org/doi/full/10.1056/NEJMoa2034545?query=featured_coronavirus
SPOILER: It’s not high. At all. https://www.nejm.org/doi/full/10.1056/NEJMoa2034545?query=featured_coronavirus
I hadn’t looked into it because it seems clear that previous infection will provide protective immunity to the vast majority over at least 6 months (study length), but you've still gotta show it to be confident and this study has done that with a very reassuring data set.
The thousands of NHS staff included in the study are from diverse occupations that keep our hospitals ticking. Oxford Uni Hospitals provide testing for symptomatic or asymptomatic staff working at some hospitals, so they can gather lots of data to generate studies.
It’s essentially a large seroprevalence study consisting of 12.5k HCW. At the outset, they identify anti-spike seropositive individuals (indicative of previous SARS-CoV-2 infection) and compare their chance of subsequent infection/reinfection to seronegative individuals.
For seronegative HCW (11,364 individuals consisting of infection-naive & post-infection low titer), 2% went on to record a +ve qPCR result, with about half being symptomatic and the rest picked up in asymptomatic screening.
So how good is the immunological memory of NHS workers?
So how good is the immunological memory of NHS workers?
Very good! : in seropositive HCW (1,265), only two +ve PCRs were documented over 31 weeks, and both were asymptomatic. Not one symptomatic case recorded. That’s a 0.16% chance of possible asymptomatic reinfection, and 0% chance of symptomatic reinfection (in this study).
Only 1 of 1,021 HCW seropositive for both anti-spike and anti-nucleocapsid antibodies went on to record a positive qPCR result. So a very clear, unambiguous seropositivity correlates with significant protection in individuals with high risk of exposure.
Rather than calculating a percentage (which I did simply for ease of understanding), the authors use qPCR+ve per 10k days at risk, which is more complex to understand on first glance but makes the point.
That analysis results in (for me) the key figure of the study.
That analysis results in (for me) the key figure of the study.
An interesting observation was that individuals with titers just below the positive threshold for anti-S or anti-N (nucleocapsid) assays, defined as “high negative” titers were protected. This suggests a previous infection resulting in T/B cell memory despite waning Ab titers.
“... it is likely that other health care workers with baseline titers below assay thresholds, *which were set to ensure high specificity* , had been previously infected with SARS-CoV-2 and had low peak postinfection titers…”
The study also goes into more detail on the three possible cases of reinfection. When I look at the table provided, I wouldn’t put my hand in the fire for these being top-drawer evidence of reinfection. Perhaps a mild one in "Worker 2". But it's an interesting table.
Two of the seropositive HCW with subsequent qPCR +ve results had "discordant" antibody results, which means they tested positive for *either* anti-spike or anti-nucleocapsid, but not both. So it's possible that these were actually a rare false positive.
So if you are one of the people who had Covid-19, recovered and will continue to help us through the crisis, take heart in this data which suggests that you are likely buzzing with protective immunity, ready to do what it does.
I presume that this data also applies to other key workers at elevated risk of encountering SARS-CoV-2 (see this article).
When I think of occupational hazards, Covid-19 is a nasty one. At least those NHS workers who recovered it can carry confidence.
https://oem.bmj.com/content/oemed/early/2020/12/01/oemed-2020-106731.full.pdf
When I think of occupational hazards, Covid-19 is a nasty one. At least those NHS workers who recovered it can carry confidence.
https://oem.bmj.com/content/oemed/early/2020/12/01/oemed-2020-106731.full.pdf
