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The Delta Variant and Its Risks: Overview, Implications, and (Brief) Policy Analysis

Originally posted on August 2, 2021 — Updated on August 18, 2021

Background and Overview

I am sending this update of my original August 2 document to incorporate new data, and out of concern that the risks posed by the Delta variant are still not sufficiently reflected in U.S. policy, in U.S. government statements, and in media accounts.  In some cases, it appears that important information about Delta variant risk, particularly to vaccinated people, is being deliberately understated or suppressed, and/or that Federal agencies are very slow to update public information and guidance.  Federal policy has changed only marginally since the Delta wave began, and now lags many other nations (Israel, much of Europe) by failing to implement measures that would sharply reduce cases, hospitalizations, and deaths.

Delta variant covid has already caused unprecedentedly rapid growth in covid cases, serious illness, hospitalizations, long covid, and deaths, both in the U.S. and in other nations, which if not stopped could soon cause a U.S. and global public health crisis.  The U.S. population is particularly exposed as a result of Federal policy failures, disinformation, and political and popular resistance to masking, testing, distancing, and vaccination.  The last two weeks (ending August 16) have seen some moderation of U.S. case growth from over 45% per week to perhaps 20% per week.  However, growth remains disturbingly high, and higher growth rates may resume soon due to the Labor Day weekend, corporate return-to-work plans, resumption of in-person schooling for the fall semester, and then later the arrival of holidays and cold weather.  These drivers could easily generate horrifying growth in cases, hospitalizations, long term symptoms, and deaths, particularly among children and the elderly.

About two months ago, I started receiving personal reports that fully vaccinated people were contracting covid.  Since then, these reports have sharply increased, and now include multiple reports that healthy, young, fully vaccinated people are becoming seriously ill; are contracting covid even while outdoors; and that some fully vaccinated people seemingly suffer from “long covid,” i.e. continuing long term symptoms such as vertigo and fatigue.  This prompted me to look further, and my findings were, and continue to be, extremely disturbing, as follows:

  1.  The Delta variant is dramatically more contagious to both vaccinated and unvaccinated people, and may cause more severe illness both in vaccinated and unvaccinated people, including children, than previous covid variants.  Delta can cause serious illness in vaccinated people and in children, can be transmitted by fully vaccinated people to others, and can cause infections outdoors.  New evidence also strongly indicates that vaccine protection against Delta declines sharply over time.  The combined result is that Delta is causing far more rapid growth in covid cases, hospitalizations, and deaths than previous covid waves.

Contagiousness.  Delta is three to four times as contagious as earlier variants.  With earlier covid variants, an infected person infected on average 1 to 3 additional people; the most widely accepted estimates are between 1.6 and 2.  With Delta, this number appears to be between 4 and 8, with the most widely accepted estimate being about 6.  Due to its highly contagious nature, Delta is causing a far more rapid growth in cases than has ever been seen before.  Delta can also infect people in a wider array of situations, including outdoor situations which were quite safe from pre-Delta covid infection.  Moreover, with Delta, the protection against infection afforded by full vaccination is sharply reduced relative to earlier variants.  Fully vaccinated people can become infected with Delta, and can infect others, particularly in the same household.  While full vaccination seemed to offer nearly complete protection against earlier variants, Delta can and does infect fully vaccinated people in large numbers.  This problem is compounded by declining vaccine efficacy over time, which is particularly dangerous for the elderly, who were vaccinated earliest.

With Delta, vaccination still greatly reduces both the chance of infection and the average severity of disease, but in high risk environments, the incidence of infection among vaccinated people is clearly still quite high.  It is also now clear that Delta can cause severe and/or long term illness even in some vaccinated people (see section 2, below).  The elderly and children are particularly at risk.  Israel, one of the most highly vaccinated nations, is experiencing extremely rapid growth in covid cases.  Fully vaccinated people now account for 50% of new cases in Israel.

Decline in vaccine protection over time.  The Israeli data also shows that protection afforded by full vaccination declines over time.  Here is an interview with Israel’s director of public health: 

This was first reported widely in the United States in a New York Times article of July 23:

Subsequently a new, not yet peer-reviewed, study by the Mayo Clinic confirmed that with Delta, the efficacy of both Moderna and Pfizer vaccines declines sharply over time, within six months.  The study finds that the effectiveness of the Pfizer vaccine declines much more sharply than Moderna.  Here are two links describing these results, first a popular account:

And here is the preprint of the journal article describing this study:

Finally, on August 16, the New York Times mentioned for the first time, briefly and obliquely at the end of an article principally about a Federal policy decision to recommend booster shots, that Israeli data indicates that the efficacy of vaccines declines over time not only with regard to infection but also with regard to serious illness.  Here’s the link:

However, on May 1, just as Delta started to have significant effects in the U.S., the CDC stopped tracking U.S. “breakthrough infections,” i.e. covid cases among persons who are fully vaccinated.  Stunningly, as of August 16, the CDC still has not resumed tracking U.S. breakthrough infections.  However, there is clear evidence that many breakthrough infections are occurring.  Here are three articles describing two recent large outbreaks in the U.S. where most of the victims were fully vaccinated.  First, a CDC description of one of these episodes:

This is a less technical account of the same episode:

And here is a different recent episode of large scale breakthrough infections:

2. Contrary to most government and media statements, Delta can cause very serious illness in fully vaccinated as well as unvaccinated people.

There is not yet extensive, published data on the incidence of severe illness caused by Delta among the vaccinated in the United States.  This is in itself disturbing, because the data exists.  Indeed, there is already published data from Israel.  On August 9, Haaretz published this article based on newly released data from Israel’s public health authority:

The Israeli data is updated through August 15 here, in an article also announcing new restrictions on movement and gatherings:

The Israeli data does indeed demonstrate that vaccination sharply reduces risk, but the data also demonstrate that the fully vaccinated, and particularly the elderly, still face significant risk of serious illness.  For both vaccinated and unvaccinated, risk of serious illness rises sharply with age, but the relative protection afforded by vaccination declines with age.  For the 60-69 age group, the risk of “severe” disease (which in Israel’s definition requires hospitalization for multiple days) by the vaccinated is only one eighth the risk faced by the unvaccinated.  But for the 70-79 age group, the ratio is one fourth.  It is not yet clear whether this effect is purely age-related, or is partly because older persons were vaccinated first, and therefore more time has elapsed since their last vaccination, causing time-dependent weakening of vaccine protection.

What is clear is that vaccinated people can become very seriously ill by a more commonsense definition.  I have now received multiple personal reports of healthy, fully vaccinated people becoming quite seriously ill – in one case requiring a week in the hospital, in another case being bedridden for two weeks with high fever.  I have also received personal reports of a few fully vaccinated people who appear to have “long covid,” i.e. continuing chronic symptoms such as vertigo, chronic fatigue, shortness of breath, and/or loss of one or more senses.  For the first time, on August 17 the New York Times published an article discussing the increase in Delta breakthrough infections and their potential to cause serious illness.  According to data collected by the Times for six states, breakthrough cases now account for about 18-28% of all U.S. covid cases, and 12-24% of hospitalizations:

There is also the risk of long covid.  The Delta wave in the U.S. is too new for there to be clear evidence of the incidence of long covid among U.S. Delta victims and/or among the vaccinated.  Indeed, there is is very little published analysis of long covid among breakthrough infections even from earlier variants.  However, a recent article reporting on a small group found that 19% of pre-Delta breakthrough infections caused symptoms lasting more than 6 weeks:

Recent studies also suggest that among the unvaccinated, long covid is disturbingly common, affects children as well as adults, and is often serious, e.g. sufficiently serious to preclude school, work, and/or exercise.  One study published in Nature found that 26% of pre-Delta covid patients, mostly unvaccinated, had symptoms more than six months after infection:

It is too soon to know what fraction of Delta infections result in long covid.  It is also therefore too early to know what fraction of Delta breakthrough covid victims will then suffer from long covid, but my own small sample suggests that it is at least 10%, and possibly higher.  It is definitely NOT zero; this is one example of another disturbing observation, namely:

3. Recent government statements and media reports have frequently understated the danger that the Delta variant poses to vaccinated people, including the elderly, and to children.  In some cases government agencies, e.g. the CDC, and senior government officials, e.g. Anthony Fauci, appear to have deliberately understated these risks, perhaps out of fear of discouraging people from getting vaccinated.

We now know that the CDC was aware that Delta was highly contagious, including to vaccinated people, and was causing breakthrough infections in the U.S., since approximately July 20 and that it did not publicize this information until an internal CDC presentation was recently leaked to the Washington Post:

See also:

Pattern / history of inadequate, slow, and misleading CDC statements.  After the Washington Post leak, the CDC finally began to post statements on its website about Delta.  But despite the CDC having itself analyzed and described one of the early “breakthrough” episodes, the CDC continues to understate the dangers posed by Delta – both its contagiousness and the danger it poses to those infected, and particularly risks faced by the vaccinated, the elderly, and children.

From late July, when the CDC posted information about the Delta variant on its website, until at least August 13, the CDC website still said the following: “The Delta variant is highly contagious, nearly twice as contagious as previous variants.”  This statement has recently been changed to “more than twice.”  In a graphic on the same page, the CDC similarly says:  “The Delta variant…may cause more than 2X as many infections”.  Here’s the link:

But both of those statements are misleading.  There is now wide agreement that the Delta variant is actually three to four times as infectious as previous variants.  On the same web page, the CDC does also mention that fully vaccinated people can contract Delta and also spread it.  However, the CDC page makes no mention whatsoever of the fact that fully vaccinated people can become seriously ill, when it is now known with certainty that some fully vaccinated people, even healthy young people, can and do become seriously ill through Delta infections (discussed below).  The CDC page also fails to mention that vaccine effectiveness declines sharply over time, despite clear data to this effect from both Israel and the Mayo Clinic study.

Equally disturbing, many government announcements and media reports continue to understate the danger posed by Delta infection to vaccinated people, including healthy and/or young people.  As mentioned earlier, the CDC web page on the Delta variant does not even mention that vaccinated persons can have serious illness.  Indeed recent CDC statements, as well as articles in the New York Times and elsewhere quoting government officials and medical experts, often state that when fully vaccinated people do get Delta variant covid, they nearly always are either asymptomatic or have only mild symptoms.  This is absolutely not consistent with the Israeli data, nor with the personal reports I have received, including from medical professionals with recent direct experienceOn the contrary, I have now heard many reports of healthy, fully vaccinated people who have high fevers, are confined to bed for a week or more, experience severe fatigue, and/or lose multiple senses (taste, smell, balance, hearing).  Some of them have now had symptoms for multiple weeks.

As this update is being distributed, on August 18, the CDC has finally held a press conference devoted to Delta and acknowledging the significance of breakthrough infections.

Dr. Anthony Fauci.  Appearing on Face The Nation on August 1, Fauci downplayed the risk posed by breakthrough infections.  Here is a direct quote from Dr. Fauci’s television appearance:  “…we found that individuals who get breakthrough infections, namely people who are vaccinated, who might get infected, almost invariably they get either minimal symptoms or no symptoms at all.”  Here is the full transcript of Fauci’s appearance:

Similarly, many public statements from both government and media sources emphasize that hospitalization is rare for vaccinated people who contract Delta covid (about 1-2% of cases).  This may be true, or may be an underestimate based on pre-covid data; but in either case, it is also misleading.  Covid can destroy your life even if you’re never hospitalized.  You can have a high fever, be severely fatigued, have trouble breathing, have vertigo, and lose your sense of taste and smell – without qualifying for hospitalization.  Similarly, most long covid symptoms do not qualify someone for hospitalization, even if the person is incapacitated, and unable to work or care for themselves.  In fact, many long covid sufferers had initially mild symptoms.

Lastly, most national media coverage and government statements have portrayed the Delta surge in both cases and hospitalizations as primarily driven by states with low vaccination rates and/or anti-masking laws, implying that states with higher vaccination rates and/or stronger regulation are being spared.  This is flatly false.  Over the last month, the state with the highest growth rate in new covid cases in the entire U.S. is Vermont, which also has the highest vaccination rate of any U.S. state.  Covid cases in Vermont grew nearly a factor of ten in the last month (from a seven day average of 10 cases on July 12 to a seven day average of 95 on August 12 – and 126 new cases on August 12 alone).  Over just the last two weeks ending August 12, high vaccination states with higher covid case growth rates than Texas and Florida include not only Vermont (263% growth in the last two weeks) but also Hawaii (176% growth over the last two weeks), Oregon (144%), Washington state (146%), New York (108%), and Washington DC (158%), versus Texas with 72% growth in covid cases over the two weeks ending August 12, and Florida with only 50% growth.  California is slightly behind Florida with 48% growth.

Furthermore, high-vaccination states are also experiencing high growth in hospitalizations.  The seven day average for hospitalizations over the two weeks have increased 425% in Vermont, 140% in Hawaii, 70% in Washington state, and 128% in Oregon.  This is not to say that vaccination rates and masking policy are unimportant.  Without question, the policies of Florida, Texas, and other “resistant” states have worsened their problems, and the health care systems of Florida and Texas are already under severe stress:

However, multiple high-vaccination regions are also experiencing severe stress in hospitals and ICUs.  This article about Santa Monica, CA appeared in the New York Times on Aug 1:

On August 13, Oregon called up the National Guard for deployment in overloaded hospitals:

And on August 17, the New York Times reported that Federal government data indicates that 20% of all U.S. ICUs are at 95% capacity or more; some are already well over capacity.

For recent U.S. national and state-level data on both cases and hospitalizations, see:

Finally, U.S. covid deaths are also already increasing sharply, even though deaths lag new cases by a month or more.  On July 12, there were 273 covid deaths in the U.S.  On August 12, one month later, there were 1,022.  Deaths are currently increasing over 40% per week.  Given the lag between cases and deaths, the U.S. could soon experience over 2,000 covid deaths per day.

4. Given conditions prevailing in the United States (and some other nations), in the absence of prompt government action the Delta variant could cause a major public health crisis, worse than any previous covid wave.  Resumption of in-person schooling is a major risk, as are corporate return-to-work plans and, later, colder weather.

Given the specific circumstances of the United States, the highly contagious nature of the Delta variant represents a threat potentially worse than any previous covid wave.  Both the U.S. and many other nations have recently experienced an unprecedentedly rapid growth in covid cases that, if continued in the United States, would overload the U.S. health system within a few months.  Very recently – in the last two weeks – the U.S. case growth rate has moderated from over 45% per week to perhaps 20% per week, probably due to increased popular awareness of Delta and its risks.  However, this may well be a short pause before the resumption of higher growth, for reasons discussed below.

The initial U.S. Delta surge.  Consider first the case numbers, which can be seen by googling “covid cases (nation name)” or, in the case of the U.S. and individual states, by looking here:

In late June, the U.S. seven-day average of positive covid tests reached a trough of about 12,000 per day.  As of August 12, the trailing seven day average of new cases was 126,000 per day; by August 17, it was 141,000.  But because of the Delta variant’s high growth rates, this understates the problem.  More accurate would be the average number of new infections identified over the last several weekdays.  On August 9 there were 178,000 cases; on August 10, 162,000; on August 11, 155,000 cases; on August 12, 138,000; on August 13, 186,000, on August 16, 259,000; on August 17, 144,000.  The last two days (Aug 16 and 17) yield an average of 201,000 cases per day, probably the most accurate estimate of the current situation, and 18% higher than the same two days one week previously.

If this growth rate continues, by the end of October the U.S. will experience over 1 million new cases per day.  This is totally unprecedented.  For comparison, in the last major covid wave in the U.S. (during the fall and early winter of 2020-21), it took more than four months for cases to grow by a factor of nine.  In that wave, the seven day average of new cases went from a trough of about 35,000 in September 2020 to a maximum seven day average of about 250,000 in January 2021.  Even this stark comparison probably understates the rate at which Delta is growing, because there is far less testing now than previously (discussed below).

Over the last two weeks there has been a decline in the U.S. case growth rate from about 45-50% per week to perhaps 20% per week.  This may signal a peaking of the Delta wave, but probably not.  More probably it is a pause due to population and/or institutional reactions to the Delta wave, since many companies, local governments, and individuals have started to change their policies and behavior.  For reasons discussed shortly, high growth could easily resume in a few weeks.  However, recent deceleration in case growth may also be due in part to simple undercounting, because another major aspect of U.S. policy failure is inadequate testing.  First, there is simply far less testing now than previously – about 1.2 million tests per day in mid-August, versus over 2.2 million per day during previous peaks.  Second, testing is now far less widely and conveniently available, and no longer always free.  And finally, testing is now growing far more slowly than new cases.  This suggests that new cases, and particularly asymptomatic or mild cases, may now be seriously undercounted.

Several other nations have also recently exhibited rapid growth in cases due to Delta.  In Israel, infections declined to under 50 per day and remained there for several months ending in late June.  But between June 21 and August 16, the seven day average of new infections in Israel grew from 43 to about 6,000, a factor over one hundred, and have continued to grow since at a rate of over 30% per week.  On August 16, there were 8,700 new cases in Israel.  In France, the seven day average of daily new cases rose from under 2,000 at the end of June to over 23,000 per day currently.  In Germany, the seven day average of daily cases has grown by more than a factor of seven in the last six weeks (from under 600 to over 4,000).  In Spain, the seven day average of daily new cases rose from about 3,500 per day in late June to over 25,000, then declined to 17,000 over the last two weeks, for unclear reasons, only to rise again to over 27,000 on August 16.  In Holland, daily new cases rose from a seven day average of 606 on July 1 to over 10,000 in only two weeks, when a strict regime was re-imposed, including banning all large gatherings until August 14.  In Greece, the seven day average has risen from under 400 in late June to over 3,000 in mid-August.

Hospitalizations.  In early July, the U.S. had about 17,000 covid patients in hospitals.  By mid-August, the number was well over 80,000.  In Israel, there has already been a recent, sharp increase in hospitalizations and more serious cases:

In the U.S., there is already strong evidence that high vaccination rates do not prevent rapid growth in hospitalizations.  Vermont, the state with the highest rate of vaccinations, is not only the state with the highest growth rate in cases, but also leads the U.S. even more strikingly in hospitalizations (415% over the last two weeks), and again Hawaii (133% growth in hospitalizations) and Oregon (128%) also both show higher growth in hospitalizations than either Texas (97%) or Florida (89%), with California again just behind them (84%).  Massachusetts, another very high vaccination state, has 99% growth in cases and 66% growth in hospitalizations.

Children.  The potential impact of Delta on children, and the inadequacy of government discussion of it, is particularly disturbing.  First, there is some very recent, still impressionistic, but increasingly compelling evidence that Delta may cause serious illness in children more frequently than previous variants.  Across the U.S., covid cases in children are approximately doubling every week, are already running over 100,000 per week, and already constitute 20% of all new covid cases.  See for example:


And also:

The U.S. now has more children hospitalized with covid than at any previous point, and many children’s hospitals are already over capacity.  It is also clear that some covid-infected children, perhaps 10%, suffer from long covid.  See for example:

Covid growth drivers in coming months:  schools, work, and weather. In many nations, including the U.S., recent growth rates are dramatically higher than were seen in any previous covid wave.  But the U.S. and many other nations also will soon face three additional risk factors:  the return of in-person schooling, often starting in late August; corporate and in some cases government return-to-work plans; and the arrival of colder weather.

Schools and colleges, even when teachers are vaccinated and students are masked, are a major risk factor for children due to Delta’s increased contagiousness and the low vaccination rates of children and young adults.  No children under 12 are eligible for vaccination, and even for the 12-18 age group, whose vaccination requires parental consent, vaccination rates are low and vaccination prospects are poor.  About 20% of U.S. parents in a recent poll stated that they would refuse to vaccinate their children.  Some states including Florida, South Carolina, and Texas have policies and even laws opposed to requiring masking in schools.

Return-to-work plans are another major risk.  Approximately half of the U.S. workforce has already returned to work; of the other half, about one quarter plans never to return, while the other quarter is covered by corporate return to work plans.  These plans have return dates that are heavily concentrated in September and October, in part to coordinate returning to work with the start of schooling.  As of last week, very few of these plans have been changed.  See:

And starting in November, weather and the winter holidays will again become drivers of indoor gathering and risk.  It will become far more difficult to dine outdoors, play outdoors, et cetera.  The Labor Day weekend, the resumption of full-stadium NFL football, and the winter holidays will all pose significant risks.  For all these reasons, resumption of very high growth rates and the onset of a major U.S. public health problem are all too plausible.  The totality of U.S. covid risk drivers is sobering:

  •  Delta is far more transmissible than previous variants, can infect people outdoors, and can both infect and be passed on by vaccinated as well as unvaccinated people;
  • Delta appears to cause illness at least as serious as earlier variants;
  • Only about half of the U.S. population has been fully vaccinated, and much of the remaining population is vaccine-averse
  • U.S. vaccination policy has major flaws, with the result that vaccinations are now running at far less than one million per day (around 700,000 recently);
  • Children under 12 are not yet eligible for vaccination;
  • A significant fraction of the U.S. population refuses to wear masks or take other preventive measures, and several U.S. states (Florida, Texas) have legislated against requiring protective measures;
  • Many K-12 schools, colleges, and universities will resume in-person classes within 6 weeks in most of the U.S.;
  • NFL football is currently scheduled to begin soon, with stadiums at full capacity;
  • No major areas of the U.S. are currently on lockdown;
  • Many regions, governments, and industries in the U.S. are in the process of resuming normal operation; and
  • Unlike other nations, in the U.S. no major policy measures are being taken currently in response to the above.

If the U.S. goes from roughly 200,000 infections per day currently to over a million per day by late fall or early winter, there will be very little time for the health care system to prepare.  Furthermore, these preparations and responses will need to be far more drastic than previously, and may require more personnel, money, and physical infrastructure, given Delta’s highly infectious nature.  In fact, the U.S. health care system and other important systems (police, fire, public health, utilities, legislatures, the media) may themselves be significantly degraded by the sharply rising level of covid infections within them, including among the vaccinated.  In the Western U.S., this will also coincide with wildfire season.  The potential result is extremely painful to contemplate, and it will only be averted through a combination of general individual action (staying at home, wearing masks, getting vaccinated, etc.) and very prompt, forceful government policy.  None of this is currently visible.

5. Federal policy continues to lag U.S. needs, the available Federal legal authorities, and policy measures now being taken by several other countries.  In the absence of effective government policy, it would be prudent for individuals and organizations to prepare for a very serious problem.

The Federal government has always had the authority to mandate vaccination for members of the military and for Federal workers.  However, vaccination for active duty military personnel was only mandated on August 9, and all other Federal workers still retain the right to refuse vaccination if they agree to be routinely tested.  The Federal government also has wide authority to require vaccination for interstate activities, including for example requiring proof of vaccination for all interstate travel, but has not done so, apparently out of fear of political “blowback.”

As of August 16, neither the CDC nor any other Federal agency has made a clear statement about the danger that Delta poses to the vaccinated or to children.  Given the infectiousness of Delta, this will unquestionably result in many additional infections.  Indeed, the absence of effective Federal policy response is so pervasive and striking that I am now writing a separate document devoted to policy issues, which I hope to distribute shortly.

In the absence of effective Federal policy, a variety of individual and organizational measures are still possible, and would yield major individual and societal benefits.  These preventive measures might include:

For organizations and their employees, clients, visitors, etc.:

  • Mask and vaccination mandates, routine testing, and working from home

For individuals:

  • Wearing a mask
  • Distancing, working from home
  • Avoiding indoor spaces wherever possible
  • Avoiding dense crowds, both indoors and outdoors
  • Getting a booster shot (must be done covertly in the U.S.; Israel is already administering them officially)
  • Using HEPA air purifiers / filters
  • Using at-home covid tests before socializing
  • Using delivery services
  • Stocking up on food, first aid supplies / medicines, etc.

This Post Has One Comment

  1. Anonymous

    Fantastic Post!

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