Monday, January 24

Zero Covid worked for some countries, but high vaccine coverage is key now


Since the start of the pandemic, several countries have adopted a zero Covid strategy, with the goal of eradicating Covid within their borders. Faced with the highly transmissible delta variant, many are now abandoning it.

New Zealand is the last country to abandon the Covid zero approach, following hard on the heels of Vietnam and Australia.

Vietnam was once hailed as a Covid Zero hit, but has recently experienced a sharp increase in deaths. Despite a population of 97 million, Vietnam managed to keep cases below 3,000 until May 2021, when the delta variant began to spread internationally. In October, there was 800,000 cases, and Covid deaths had risen from 35 to 20,000.

China, Hong Kong and Taiwan They are the remaining strongholds of Covid zero. How long they will continue with this strategy is anyone’s guess.

Different approaches

Countries that quickly closed their borders, once initial reports of a new epidemic emerged from China in January 2020, were able to implement zero Covid strategies and keep death rates low. Effective border quarantines were easier for island nations. But countries with strong central political control, such as China, were also able to implement this strategy.

Control strategies are on a spectrum, from a laissez-faire and chaotic approach characterized by denial, in the case of brazil; and a laissez-faire civil libertarian approach to relying on disease-induced herd immunity, in the case of Sweden. To a zero Covid approach at the other end of the spectrum, such as persecuted by China.

There is no doubt that countries that adopted a zero Covid strategy saved thousands, if not hundreds of thousands, of lives. The most important lesson, however, is not to find and adhere to a strategy, but to constantly follow the science.

Infectious diseases and our responses to them have evolved. Simple data on the transmission power of the delta variant shows how the ability of SARS-CoV-2 to mutate under conditions of rampant infection has changed the rules of the game.

Viral load, which is the concentration of the virus in the throat and nose, is 1000 times greater with delta than with the original virus. The reproductive number, which is the average number of people to whom an infected person will transmit the virus, averages 5.1 for delta, compared to 2.8 with the initial virus. This is the difference between a possible 200 additional infections transmitted from a single case in three weeks, compared to 15 new infections with the original virus.

Zero-Covid has been effective in preventing deaths and allowing a certain level of normalcy within national borders in countries that moved quickly to close their borders and where geographic, political and economic factors were favorable. No country in Europe or America tried. But the big jump in the virus’ transmissibility and the rapid development of highly effective vaccines has forced changes in the response.

A high price to pay

The most prominent countries now are those, like Singapore, that kept case and death numbers low and moved quickly to achieve high levels of vaccine coverage. New Zealand and Australia, in 40% -50% coverageThey are playing catch-up on vaccines and are at risk. China has reached 75%, but Taiwan and Vietnam are far behind.

Covid disease and transmission in children are rare. Therefore, the critical goal that countries must achieve is coverage greater than 90% in adults, which Denmark, Ireland and Portugal They have reached. But vaccine breakthrough – that is, fairly mild infections in fully vaccinated people – is now common. And countries have started booster vaccination programs to boost immunity in the elderly and vulnerable.

Taiwan successfully controlled its first big wave of Covid between May and July 2021. And daily cases in Hong Kong have been in single figures since April. But they need to move quickly to high levels of vaccination coverage before these strategies begin to unravel. Unless a new generation of vaccines can provide much higher protection, regardless of emerging variants, the era of Covid zero will not return. The exception will be when countries can combine high vaccine coverage, virtually complete isolation, and rapid, draconian lockdowns when viruses break through these barriers. Perhaps China, alone, can do it.

If Covid cases and deaths are the only measures of success, China ranks first overall due to its ability to control personal life and public behavior, and its ability to quickly switch to a vaccine-led strategy. However, people living in democracies that guarantee a high degree of personal freedom may find the cost of an epidemic-free society too high.The conversation

Ruairi Brugha, Emeritus Professor of Public Health and Epidemiology, RCSI University of Medicine and Health Sciences

This article is republished from The conversation under a Creative Commons license. Read the Original article.


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