Representative antibody study of Iquitos, Peru, after their devastating 1st wave. Over two-thirds of the sample had SARS-CoV-2 antibodies, suggesting 70% of the city had been infected. Children were more likely to have antibodies than adults (except >=60). thelancet.com/journals/langl…
Although 70% of the city’s population had previously been infected, this was insufficient to prevent a second wave beginning in January 2021 caused by the P.1 variant. This suggests herd immunity can’t be reached by natural infection, which is less effective than vaccination.
Interestingly, a very high proportion of children had been infected, despite school closures. However, Iquitos is a very poor city and most residents have to leave home to purchase food on a daily basis. Children are likely more exposed to the community than in other settings.
Supporting this, the authors report that a similar antibody study was done at one of the country’s markets. Over 99% of people working at the market had antibodies against SARS-CoV-2.
Iquitos was one of the first cities in the world to pass the herd immunity threshold for the original strain of the virus, but the city “paid a considerable cost in terms of human suffering and deaths” and did not a avoid a second wave driven by the more dangerous P.1 variant.
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There are now clear signs of a growing B.1.617.2 epidemic in the UK.
While cases caused by the B.1.1.7 (alpha/UK) variant are decreasing, B.1.617.2 cases are growing. The majority of S-gene positive cases depicted in green in the graph below are likely to be B.1.617.2 cases.
Study of 3 UK variant (B.1.1.7) outbreaks in childcare centres in Hesse, Germany, showing that children and adults were similarly likely to be infected, and that children and staff were similarly likely to transmit the virus to their household contacts. 🧵 eurosurveillance.org/content/10.280…
In this study, outbreaks were studied in 3 childcare centres.
Except for one childcare centre, where more adults than children were infected (53 vs. 31%), an equal proportion of children and adults were infected (27-28% in centre 2, and 17% in centre 3).
The authors then looked at the household contacts of the infected staff and children.
Overall, they found that 37% of contacts were infected (32% of child contacts and 39% of adult contacts).
(1/4) Vietnam has reported the emergence of a variant which combines elements of the UK (B.1.1.7) & Indian (B.1.617.2) variants. According to the Health Minister it could spread “very fast” in the air.
➡️ straitstimes.com/asia/se-asia/v…
Vietnam is struggling to contain the new variants.
(2/4) A common feature of coronaviruses is their ability to exchange their genetic material (recombination).
This probably happens in all infected people. As the virus reproduces, its copies may exchange genetic material with each other.
Most changes are probably unremarkable.
(3/4) But it’s also possible for people to be infected with different variants at the same time. This is riskier. The more community transmission there is, the more likely this is to occur.
1. What proportion of the population needs to be vaccinated to achieve herd immunity? It depends on a number of factors, including how contagious a virus is, and how well a vaccine can prevent infection.
Even very contagious variants can be stopped if efficacy is high enough. 🧵
2. This is a very simple model with lots of assumptions, but gives a rough idea of what we need to aim for to achieve herd immunity against SARS-CoV-2.
Four theoretical vaccines are shown, with 60 to 90% efficacy against infection.
3. Vertical lines mark estimates of the contagiousness of the original strain of SARS-CoV-2, the UK (B.1.1.7) variant, & the Indian (B.1.617.2) variant.
The proportion of people needing to be vaccinated (vertical axis) is the point where the vaccine & variant lines intersect.
I hope I’m wrong about the variant, but there are warning signs from multiple countries that the Indian variant is more transmissible than the UK variant.
This means that the measures that previously worked to keep people safe may not be enough now.
It does not mean that the situation is hopeless (it isn’t), or that getting infected is inevitable (it’s not).
The variant can’t break the laws of physics, so masks and ventilation still work. But you may have to step them up (i.e., use better masks, and increase ventilation).
Here’s a very good news story. New studies show the Pfizer-BNT vaccine works incredibly well, including against the South African variant (the most immune-evading variant known).
But the second dose is critical.
The Novavax vaccine also holds up well against the SA variant. 🧵
Real-world data from Qatar show the Pfizer-BNT vaccine is effective against the UK and South African variants, but only after the second dose.
For example the vaccine was only 39% effective against severe disease after one dose, but this rose to 97% (92-99%) after two doses.
Here’s the effectiveness by first, then second dose:
Infection:
🇬🇧 29%, 89%
🇿🇦 17%, 75%
Severe disease:
🇬🇧 54%, 100% (82-100%)
🇿🇦 0%, 100% (74-100%)
Any variant: 39%, 97% (92-99%) nejm.org/doi/full/10.10…