Hospitals are likely to struggle but boosters will help, predict two new studies
The Economist
December 28, 2021
IT HAS BEEN less than a month since Omicron, the latest covid-19 variant of concern, was first spotted by scientists in South Africa.
In just a couple of weeks Omicron has probably reached almost every country in the world and is now the predominant variant in several countries, including Britain, Denmark, Norway and parts of southern Africa.
A spread this rapid leaves no doubt that Omicron will soon replace Delta, the variant that currently causes most covid cases globally.
Scientists from Imperial College in London explained what this means for the world in a pair of studies published on December 16th.
The 1st study at Imperial College
The first study rounded up data on Omicron’s spread in Britain. It found that each infection tends to produce at least three more.
That is similar to the speed at which covid was spreading in Europe in the pandemic’s first wave in early 2020, before vaccines were available or countermeasures imposed.
At this rate, cases are doubling every two days-a trend that quickly becomes an almost-vertical line when daily cases are put on a chart.
That Omicron can spread so fast in a country such as Britain, where almost 70% of the population is vaccinated and millions have had covid, is largely because of its astounding ability to evade immunity from both vaccines and previous infections.
The researchers found that in Britain a two-dose course of the Pfizer or AstraZeneca vaccine was, at most, 20% effective against infection by Omicron.
had covid in the past was also of little help, conferring only 19% protection-far less than the 85% against Delta found in other studies.
Boosters, however, can make a big difference. A third jab using Pfizer’s vaccine after an initial course of the AstraZeneca or Pfizer jab was between 55% and 80% effective against infection by Omicron.
The 2nd study at Imperial College Study & Other Institutes
These results were the basis of the second study by the Imperial College team and their colleagues at several other institutes.
In that study, they estimated how the layers of immunity in various countries-from previous covid waves and vaccination-will stand up to Omicron.
That analysis relies on estimates as to how protective the jabs might be against severe disease and how protection from boosters might wane over time.
These estimates come with a lot of uncertainty because, for now, they are derived from data on how levels of antibodies in the blood correlate with protection from covid.
Data from actual Omicron cases in hospitals will be a lot more reliable for this sort of analysis but will not be available for another week or so (because there are still not enough patients).
All told, the level of immunity of a country’s population will ebb and flow over time.
More jabs and infections will push it up. Waning protection, including that from boosters, will push it down.
If the antibody levels from boosters decay at the same or half the rate of the primary course of vaccination, the researchers reckon that after 60 days boosters may be 80–86% effective against severe covid (and need for hospital admission) in an Omicron wave.
That is encouragingly high but lower than the 97% efficacy for Delta.
Omicron is likely to stretch hospitals in all countries
The researchers then used the data on Omicron’s transmission and national immunological profiles to estimate the number of cases and hospital admissions that countries might expect when Omicron spreads.
They conclude that Omicron is likely to stretch hospitals in all countries, with peak deaths and hospital admissions similar to those in previous waves, if no restrictions to slow down its spread are put in place.
This conclusion stands even if the severity of disease caused by Omicron is one-third the severity of Delta.
Using boosters wisely, however, can save lives and alleviate pressure on hospitals.
The models predict what the effect might be in three types of countries.
- In countries with widespread infections in the past and where most people have already received a two-dose vaccination course (such as the United States and much of western Europe) …
… boosters given to people over the age of 60 could cut by 25% the total number of covid deaths occurring in 2021–2022 compared with a scenario without boosters.
- In countries where vaccine roll-out has been slow and infection rates in past covid waves were high (such as most in Africa) …
… the impact of Omicron will be mitigated by partial immunity induced by recent Delta waves.
In such countries administering boosters to older people, rather than using them for a primary course of vaccination in younger groups, would be more efficient, leading to 5–15% fewer deaths overall.
- The third set of countries are the “zero-covid” countries that had kept infection rates low throughout the pandemic (including China, Australia and New Zealand) …
… Vaccination rates there are high but use of boosters is not.
These countries are facing a tricky choice. Even if they open up after giving boosters to people over 60, they will still have large epidemics, comparable to those experienced in other countries.
But delaying re-opening until boosters are given to their entire populations to create a strong layer of immunity would take months-and is predicted to result in a worse outcome because by then booster efficacy would have waned in the highest-risk groups.
These predictions could change in the coming weeks as the severity of covid cases from Omicron becomes clearer.
If people limit their contacts, that will flatten the curve of cases and patients in hospitals.
For now, though, most countries with imminent Omicron waves have some tough choices to make.
All our stories relating to the pandemic can be found on our coronavirus hub. You can also find trackers showing the global roll-out of vaccines, excess deaths by country and the virus’s spread across Europe.
Originally published at https://www.economist.com on December 17, 2021.
