Data from the UK shows that the Delta* variant of SARS-CoV-2 is much more infectious than the Alpha variant, making it around twice as infective as the original virus. In technical terms wheras the R0 of the orginal virus was 3, that for the Delta variant is 6. The vaccines are less effective against it but full vaccination still gives good protection from serious symptoms.
The variant is also presenting different symptoms and is particularly spreading among the young in the UK. (Caution: This may be a factor of the roll-out of vaccination by age group.) For the younger, the principle symptoms are very similar to a cold; headache, coughing and a runny nose. Few have reported loss of taste or smell.
The CDC has confirmed that the variant has been found in the US where its incidence rose from 2.5% on May 22 to 6.1% on June 5. Again, this data must be treated with caution in view of the comparatively very small amount of genomic surveillance undertaken.
I am going to draw on two sources, the results from the ZOE tracking project and today’s video from John Campbell who brings together other sources.
Tim Spector OBE, lead scientist on the ZOE COVID Study app and Professor of Genetic Epidemiology at King’s College London, comments on the latest data:
“The UK picture is changing quickly now. Cases are rising, but not nationwide, it’s very much a regional issue. The North West of England and Scotland are the two regions with the highest prevalence, with rates higher than in some parts of Europe. However, the data highlights that the increase is happening in the younger age groups, suggesting the start of an epidemic in the young. We can’t be too complacent, and we are monitoring things closely.
In his video Prof. Spector details the different symptoms being reported for this variant and gives comparative figures for infection in the unvaccinated, partially vaccinated and fully protected.
The importance of completing a full course of doses is emphasised by data given by the Health Secretary, Matt Hancock (via J. Campbell).
12,383 cases of Delta variant up to June 3
- 464 reported for emergency assessment
- 126 people admitted to hospital
- 83 were unvaccinated
- 28 had received one dose
- 3 both doses of vaccine
There can be high confidence in these figures due to the large amount of “surge” testing in the areas where the variant has been found so many, but likely not all asymptomatic or low level symtomatic cases would have been picked up. >50% of samples from the “hotspots” would have be gene sequenced to confirm the variant. You may note the much lower proportion of cases “needing emergency assessment” than was usual in earlier waves. (I presume the strict by age cohort vaccination programme may well have average age of the infected lower and affected this figure.)
LESSONS FOR THE UNITED STATES
Headlines here:
- Get Vaccinated.
- Get fully vaccinated even if you have had COVID-19 in the past.
- Get to know the different symptoms in those infected by the Delta variant, particularly if your household has young adults. [CDC please look at the bl**dy data from ZOE!]
- If you have cold-like symptoms, check the new symptom list and get a test if you can.
- Ideally CDC should adapt its surveilance, testing, and sequencing regime to contain the Delta variant before it spreads and causes a further wave of infections.
The Alpha variant is dominant in the US, but not to the degree in the UK. The first dose of the Pfizer and AstraZeneca vaccine were 50% effective, i.e. complete immunity from infection which was enough to suppress the virus enough to prevent serious illness and death. In a time of rapid and wide spread, that strategy succeeded in the aim of preventing the health system becoming overwhelmed. Complete immunity from infection fell to around 33% with the Delta variant. Protection considerably improves with the second dose to around 88% protection from symptomatic infection.
Those most at risk are the unvaccinated followed by the partially vaccinated (ie not 2 weeks after the second dose.) It is by the way not advisable to exercise for a few days after the injections. If you are feeling a bit yuk, don’t try to “run it off” or hit the gym.
The further increase in the R0 to 6 also has implications for when a community will reach “herd immunity”. The more infective and able to evade existing immunity, the greater percentage of the herd has to have immunity. The UK Office for National Statistics carries out surveillance antibody test. The latest data shows:
Week ending 22nd May
- England 80.3% of adults would have tested positive for antibodies
- Wales, 82.7%
- Northern Ireland, 79.9%
- Scotland, 72.6%
John Campbell points out the complications of these data. The numbers who have antibodies will include around 70% of adults who had received one dose.. As could be expected, the strongest immune response was in the elderly who had been prioritised for second doses. Those who have had COVID-19 may no longer have antibodies and the degree their immune system(s) have been “trained” to produce more will vary. (Somebody treated with the full panoply of available medications may not have developed sufficient memory-T cells for example. That’s why it’s important for the previously infected to be vaccinated.)
The survey was taken at a time when the Alpha variant was well under control in the UK. Given the caveats, it is probably reasonable to assume that there was about 70-80% overall immunity, That would tie in with a study in Brazil that showed 75% was a point at which community spread was controlled. Almost all new UK hostpital admissions are caused by the Delta variant. That means it is likely that “herd immunity” will only be reached when over 80% are protected either by full vaccination or infection-acquired immunity. I fear that in the US it may have to be by the latter means.
Much will depend on the CDC’s and state health authorities’ ability to monitor and contain the outbreak of the Delta variant. The UK does have experience of thais in the case of an Alpha variant that had acquired the E484K mutation associated with greater infectivity and possibly morbidity in other variant strains. That was found and traced by genomic testing. Here the US is at a distinct disadvantage. The UK repurposed its many human genorme sequencing machines to sequence SARS-CoV-2. In the US the genome sequencing capacity varies from state to state. IIRC Dr Fauci proposed expanding the CDC’s capacity to do as many sequences in a month than the UK genomics services do in a day. The data available in the US is very much less detailed. It’s important to identify if a surge in cases is caused by the new. introduction of the Alpha or the Delta variants.
The UK has been doing “surge testing” in areas where the variant has been found. As well as community based testing, packs of lateral flow tests have been given out door-to-door in the most affected town. This is now being extended to the other towns where the Delta variant is spreading. The pack for one person has enough materials for seven lateral flow tests and are already available free on request at pharmacies or on line. It is important to pick up asymptomatic cases of this variant to stop it spreading, especially in the young.
Here I suspect we hit two further problems. Who would provide the test kits and would they be free? The costs could be considerable given you may have to test a whole city area to identify cases.
I must caution that the UK experience and practice cannot be directly applied to the US. Most importantly there has been a high upttake of the vaccine with over 77% of over-18s now having had one dose and 54% both. So far the government has insisted on sticking to the by-age cohort rollout although some mass vaccination centres found they had over-estimated the demand from the right age group so offered the spares to over 18s. The government is under pressure to “surge vaccinate” and bypass this.
In the US of course such strict age banding has not taken place so there will be a greater proportion of older, unvaccinated people. So far all the UK data is skewed by the young unvaccinated. Consequently data about the effect of the Delta variant on older people is difficult to assess.
For the individual, it is helpful to know the variants in circulation as well as the overall COVID number of cases. It does look however that the Delta variant may have started to community spread. If there is a local spike in your area you may well want to take appropriate precautions like resuming masking in indoor and crowded areas.
In this piece I have drawn heavily on John Campbell’s videos. The unattributed charts in quote boxes are adapted from his notes to his Wednesday video felow but use his and other links elsewhere.
*Please note. I have used the WHO Greek letter designations. The above video has an Australian contributor listing all the variants and their previous names. The Alpha variant is better known as the Kent/UK variant. The Delta variant was first identified in India and is one of two that emerged there.