This article says we need a real discussion about population immunity. (Pop. Imm. Article) The author has recently changed his mind about the best strategy and now thinks we should lift the stay-at-home orders and let the epidemic run its course. He is responding in part to people who are basically saying we need to lock down forever and that even population immunity doesn’t stop all infections. He makes the point, and people are finally catching on to this, that the models wrongly assume that the population is heterogenously attacked by the virus. It isn’t, the most susceptible get infected first, and a lot of people simply don’t get infected, so population immunity is effectively achieved at a fairly low level of the entire population.
It is not just Minnesota that has a long-term care facility problem. A lot of states do according to a report from this group that focuses on coronavirus issues in long-term care settings. (LTC Report) The authors go through country by country, although data reporting and measurement issues are present in many countries and obviously different countries may have different strategies in caring for the frail elderly. But it is apparent that in most places residents of long term care facilities represent a disproportionate percentage of coronavirus deaths.
Another antibody study, this one from New York. (Medrxiv Paper) The authors examined over 1300 patients who had confirmed and suspected mild coronavirus infection. In the first two weeks the patients received both an infection and antibody test. In the third week the patients received on an antibody test. Again the antibody test misses more true positives than true negatives. 47% had a confirmed infection by a test before the survey. In the survey tests, 57% of the participants had strong positive antibody results and 5% had weak ones. Of the subset who had weak or no antibodies on the first test, 89% showed increased antibodies in the second test. There was no association of age or sex with antibody strength, but people who had symptoms longer had stronger antibody responses. Overall 99% of those tested developed IgG antibodies, the type that are the basis for long-lasting immunity. These antibodies developed over an extended period from the infection period. The researchers are going to track the group for 6 months to monitor strength of antibodies. The authors also found evidence of coronavirus genome in the upper respiratory tract for up to 28 days after symptom resolution, but this wasn’t evidence that the patients were actually infectious for that long.
Another study that tries to improve on the typical approach to infection spreading in epidemic modeling. (Medrxiv Paper) The authors noted that contact patterns used in most epidemic models were not particularly realistic and took different approaches to looking at interactions as a function of age or population density or other factors. The authors built a modified model which looked at how likely it is that two people will meet and how likely it is that virus transmission will occur if they meet. An interesting exploration of alternative ways to define contacts in models, but overall flawed by treating all individuals as susceptible of being infected, and at the same rate.
Here is a paper that explores the impact of more targeted mitigation of spread tactics. (Medrxiv Paper) The authors explored whether strategies to shield more vulnerable populations by reducing contacts with the general population, while allowing more freedom of movement to the general population, could achieve the same results as a general lockdown. They noted that few models explicitly have examined this strategy. They assumed an exceptionally high 20% of the population was vulnerable, but explored other percents. They acknowledged that a non-general lockdown would allow greater build of population immunity. They noted difficulties in modeling contacts. The model generated a “second wave”, but it was not huge. The findings, while not completely realistic, did suggest that this more targeted strategy produced epidemic outcomes not significantly worse than a complete lockdown.
And one more paper on generation of antibodies. (Medrxiv Paper) In this study, the authors looked at antibody development in 44 hospitalized patients, so they had fairly severe illness. All developed antibodies within 6 days after a positive infection test. In a neutralization test, these antibodies proved effective against the virus. So the evidence is beginning to show that we can be confident of immunity developing after infection.