Great, so now there’s no herd immunity?

Kevin Perry sent me a very disturbing news story yesterday. It’s by an internist and primary care physician practicing in Washington, DC. It describes a 50-year-old male patient of his, who after having a fairly mild case of Covid-19 several months ago – and after getting two negative PCR tests – recently contracted it again; this time, his case was much more severe, involving “multiple” trips to the hospital.

The author points to other reports of Covid-19 patients being cleared by negative tests yet becoming reinfected later. And I read more than a month ago about a South Korean study that identified 250 or so people who became reinfected. Of course, none of this is definitive proof, and there are some Covid-19 patients whose cases have dragged on for months (of course, they’re not having negative tests, either).

The author concludes by pointing to four “warning signs” from this incident. First, not only can people be reinfected with Covid-19, but the second infection may be worse than the first. This is the case with dengue fever, which is also caused by a virus.

Second, antibody production after a person is infected may not always be enough to prevent the person from becoming reinfected (the patient couldn’t get an antibody test after he was infected the first time). Antibodies aren’t an all-or-nothing proposition. They need to be above a certain threshold (currently unknown, of course). Presumably, the patient had some level of antibodies, just not enough to prevent a second infection. The same goes for the other type of “immunity”: cellular immunity, which is mediated partly by T-cells. The patient’s cellular immunity was obviously as deficient as his antibody immunity was, since he got reinfected.

Third, recovered patients who think they’re immune may relax in their interactions with other people (the patient in question probably got re-infected from a younger relative) – with terrible consequences.

Fourth, this calls into question whether an effective vaccine will be found, for two reasons: a) the vaccine may not produce enough antibodies to protect the person (or T-cells, since I believe some vaccines try to encourage cellular immunity), or b) even if it does, it may wear off quickly (the author points out the possibility that the patient did have adequate antibodies initially after recovering, but soon lost them).

Of course, work on vaccines should continue, but this is just more evidence that anyone who is betting everything on the idea that we’ll have a safe, effective and inexpensive vaccine within the next couple of years (let alone this year!) is almost certain to be disappointed. And any country (ahem!) that ignores the basics – mask wearing, widespread testing, contact tracing, isolation of cases, adequate PPD for healthcare and essential workers – in the hope that they won’t be needed soon is making a very serious mistake, which will very likely result in many more unnecessary deaths than have already occurred.

But the biggest warning sign in the article is the one advertised in its title: There may not be such a thing as herd immunity. The author points to a couple news pieces – including a July 6 opinion piece in the Wall Street Journal, which I used to think was an excellent publication but now I wonder if it should be closed as a menace to public health – that suggest maybe achieving herd immunity should be our goal at this point, ignoring the disastrous experiences of the UK and Sweden, who both initially pursued that goal.

This message is quite clear: Although there may still be something called herd immunity, anybody who suggests that it’s OK if we have huge numbers of cases, since they’ll just bring us closer to that goal, is living in a fool’s paradise. Or in the White House, which is saying the same thing.

The 7-day growth rate in total deaths declined almost steadily from a high of 641% on March 28 (meaning total deaths were almost doubling every day) and reached 3% on July 3. It stayed at that level until Saturday, when it went up to 4%. I’m certainly not looking for it to go back down anytime soon, and with the daily new case numbers now at close to three times what they were 30 days ago, it’s hard to see why that percentage wouldn’t go above 4% soon.

The projected deaths numbers still haven’t risen too much from their low a couple weeks ago, but they’ll keep going up with the 7-day rate, since that’s what they’re based on. I will regard it as exceptionally good news – faute de mieux, as the French say – if that rate doesn’t go above 4%, and later starts declining again. But that’s going to require measures like those discussed above.

The numbers

These numbers are updated every day, based on reported US Covid-19 deaths the day before (taken from the Worldometers.info site, where I’ve been getting my numbers all along). No other variables go into the projected numbers – they are all projections based on yesterday’s 7-day rate of increase in total Covid-19 deaths, which was 4%.

Note that the “accuracy” of the projected numbers diminishes greatly after 3-4 weeks. This is because, up until 3-4 weeks, deaths could in theory be predicted very accurately, if one knew the real number of cases. In other words, the people who are going to die in the next 3-4 weeks of Covid-19 are already sick with the disease, even though they may not know it yet. But this means that the trend in deaths should be some indicator of the level of infection 3-4 weeks previous.

However, once we get beyond 3-4 weeks, deaths become more and more dependent on policies and practices that are put in place – or removed, as is more the case nowadays - after today (as well as other factors like the widespread availability of an effective treatment, if not a real “cure”). Yet I still think there’s value in just trending out the current rate of increase in deaths, since it gives some indication of what will happen in the near term if there are no significant intervening changes.

Week ending	Deaths reported during week/month	Avg. deaths per day during week/month	Deaths as percentage of previous month’s
March 7	18	3
March 14	38	5
March 21	244	35
March 28	1,928	275
Month of March	4,058	131
April 4	6,225	889
April 11	12,126	1,732
April 18	18,434	2,633
April 25	15,251	2,179
Month of April	59,812	1,994	1,474%
May 2	13,183	1,883
May 9	12,592	1,799
May 16	10,073	1,439
May 23	8,570	1,224
May 30	6,874	982
Month of May	42,327	1,365	71%
June 6	6,544	935
June 13	5,427	775
June 20	4,457	637
June 27	6,167	881
Month of June	23,925	798	57%
July 4	4,166	595
July 11	5,087	727
July 18	5,406	772
July 25	5,619	803
Month of July	23,335	753	98%
Total March – July	153,457

Red = projected numbers

I. Total deaths

Total US deaths as of yesterday: 137,787

Increase in deaths since previous day: 382

Yesterday’s 7-day rate of increase in total deaths: 4% (This number is used to project deaths in the table above; it was 4% yesterday. There is a 7-day cycle in the reported deaths numbers, caused by lack of reporting over the weekends from closed state offices. So this is the only reliable indicator of a trend in deaths, not the three-day percent increase I used to focus on, and certainly not the one-day percent increase, which mainly reflects where we are in the 7-day cycle).

II. Total reported cases

Total US reported cases: 3,414,105

Increase in reported cases since previous day: 58,210  

Percent increase in reported cases since yesterday: 2%

Percent increase in reported cases since 7 days previous: 14%

III. Deaths as a percentage of closed cases so far in the US:

Total Recoveries in US as of yesterday: 1,517,560

Total Deaths as of yesterday: 137,787

Deaths so far as percentage of closed cases (=deaths + recoveries): 8%

For a discussion of what this number means – and why it’s so important – see this post. Short answer: If this percentage declines, that’s good. It’s been steadily declining since a high of 41% at the end of March. But a good number would be 2%, like South Korea’s. An OK number would be 4%, like China’s.

I would love to hear any comments or questions you have on this post. Drop me an email at tom@tomalrich.com