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The Economist April loth zozr Covid-ug vaccines Sorting signal from noise With millions vaccinated, rare side- effects of covid jabs are coming to light CHR[s wHrrrY, England's chief medical officer, vividly recalls a nerve-raciaog moment on December 8th 2020. That was the day when England became the first country to roll out a covid-r9 vaccine, a jab developed by Pfizer and BioNTech. Near in idWght on vaccination day one "we were discussing it and just thinking 'what are we dealing with here? These are small numbers and we've already had several dangerous near misses'.- said Dr Whitty in a recent talk at the Royal Society of Medi- ae. In somepcople, it had turned out, the vaccine sets off anaphylaxis, a life-threat- ening fe-threatening allergic reaction. But this is rare. It occurred just once among the 22,000 or so people vaccinated in the trial. which could have been by chance. Now, with hundreds of millions vaccinated, the rate at which it occurs is cleaner: five per million. Fortunately, this side-effect is not only extremely rare but shows up soon after the jab. And treatment for it exists. Everyone who receives the Pflrxr vaccine is now asked to stidcaround fuorc5 minutes, just in case. There have been no deaths from ana- phylaxis related to the vaccine As millions of jabs of various covid-tg vaccines are administered every day, such rare adverse reactions will inevitably emerge. On April 7th both Britain's health officials and the European Medicines Agency (caw), which regulates drugs in the European Union. said there is strong evi- dence that AstraZeneca's covid-r9 vaccine may be unload with very tare blood clots, often in the brain or the abdomen. The Em expects reached their conclusion based on a review of 86 reported cases, r8 of which were fatal. Britain's experts reached the same conclusion from data on 79 cases, h9 of which were fatal. Both the FmA and Brit- ain's drug regulator concluded that the vaccines benefits outweigh the potential risk of the dots. But Britain's officials, armed as usual with some nifty charts for their televised briefing, said thatforpeople under ;o the risks and benefits from the vaccine were 'finely balanced", so a differ- ent jab may be preferable. The investigation of the suspected clots from the Astra7eneca jab has been a prime exampleofrhe challenge ofsortingthe sig- nal of a vaccine's side-effects from the ca- cophony of medical emergencies that hap- pen to millions of people every day. Vac- cine -safety experts have two ways to un- lve whether a rare medical proh]em is Pla� at work caused by a vaccine, says lcathryn Edwards of the Vanderbilt University school of Medicine, In Nashville, Tennessee. They can compare its rate in vaccinated people against the `background' rates ofit thatare observed in the unvaccinated. And they an look for unusual features of the medi- cal condition being investigated_ The fust signals emerged in late Febru- ary, when doctors in several European countries noticed clusters of blood dots In people recently given the AstraZeneca jab, someofwhom died- Most were women un- der 6o, which was not terribly surprising because many EU countries were, at first, not convinced that the jab worked in the el- derly and used it largely for essential work- ers, such as nurses, teachers and social - care workers—professions in which most employees are women. The FMA's data as of March 22nd sug- gested that the tate of brain clots in people under the age of 6o who bad bad Astra- Zenecas vaccine was one in hoo,000— higher than would be expected normally. Precisely how much higher, though, is hard to tell. The rates of such rareand diffi- cuit-to-diagnose conditions vary a lot by country, age and sex. Estimates of the inci- dence of such brain dots have ranged from 0.22 to 1.57 cases per too,000 people per year, and they, are more common in youn- gerpeopleand women. As doctors began to look more closely, something curious emerged Many pa- tients with suspected clots from the vac- cine had unusually low levels of platelets. These are fragments of special precursor cells that float in the blood Their job is to form blood clots (they rush to the site of a ort or other bleeding). Cow platelet levels therefore usually result in uncontrolled bleeding, not dots. Comments on the Draft CAP 2.0 2021.12.22 Science & technology 73 with this new information to hand, Britain's medical regulators searched their data on vaccinated people for the unusual tandem of clots and low platelet counts. They found four cases per million people vaccinated, a rate several times lower than in the EU. One explanation is that Britain, unlike the rest of Europe, had used the jab primarily in older people. The rateat which the clots occurred in Britain declined steadily with age. importantly, Britain's ex- perts found that the clots occurred as much in men as they did in women. This combination of blood dots and low platelet counts is something that doc- tors know bow to diagnose and treat, says Jean Marie Connors, a haematologist at Brigham and women's Hospital, in Boston. It resembles a condition seen is some peo- ple who are given heparin, a drug used widely to treat blood dots. For unknown reasons, some people develop an immune reaction to heparin, which results in blood dotting so profound that it depletes their platelets. The same reaction appears to be provoked by the vaccine. Medical societies in several countries have already issued guidelines to doctors on how to spot and treat this rare reaction to the AstraZeneca vaccine. With vigilance and appropriate care, the extremely rare deaths that may result from it will become even rarer a Dorn-ast3c hcating A new use for microwaves U you can have microwave ovens, why rot microwave boilug DECARBONISING AN BODNOMY i5 a big job. Coal- and gas -fined power plants must be swapped for wind, solaror nuclear ones. Petrol -driven cars must be replaced by electric versions. Less attention is paid to beating. But in cold countries such as Britain, warming houses, offices and the like consumes more fossil fuel than etcher electricity generation or transport The fuel involved is usually natural gas. This is burned in aceatral boilerin orderto heat water that flows to radiators else- where in the building. Britain's govern- ment would like to change this. From 2025 gas -fined boilers will be banned in newly built homes. By the mid-2o3os installing new gas boilers in existing houses will be banned, too. The question Is what will replace them. Unlike electricity generation, where re- newables are proving popular, or ars, where battery -powered vehicles are rapid- ly becoming established, the market for �►