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A health worker receives a Covid-19 vaccine at a community health centre in Nanjing in the eastern Chinese province of Jiangsu. Photo: Xinhua

Explainer | How the coronavirus vaccines compare and who can get them

  • The race to carry out the biggest inoculation programme in history has begun, with six products approved and more to follow
  • What are some of the differences between the various vaccines and how many doses have been ordered around the world?
Millions of people in dozens of countries have started to receive Covid-19 vaccines as part of the effort to fight the novel coronavirus that has infected nearly 100 million people worldwide. It is the fastest vaccine development in history and one of the greatest logistical challenges the world has faced.

Here is a snapshot of the situation so far, from vaccine development to distribution, and some answers to frequently asked questions about how they work.

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How many vaccines?

National health agencies are reviewing and granting emergency use authorisations to a number of vaccines developed by different pharmaceutical companies and mass inoculation programmes are rolling out in many countries.

Six have been approved so far, using different technologies and with varying side effects. They have been developed by: US firm Moderna; US-German partnership Pfizer-BioNTech; Britain’s Oxford-AstraZeneca partnership; Sinopharm and Sinovac in China; and Russia’s Gamaleya.

The World Health Organization recommends emergency approval should only be granted after phase 3 – final stage – clinical trials, which involve thousands of people, to determine safety and effectiveness.

According to WHO guidelines, health authorities should continue to monitor for any side effects after mass inoculation starts.

There are 10 additional vaccines in phase 3 trials. Of these, a single-dose vaccine developed by Johnson & Johnson in the US could be a contender in the developing world.

How many doses?

The available vaccines require two doses for sufficient protection and some must be stored in ultra-cold facilities, creating challenges in poorer countries.

There are also differences in the timing of second doses. Moderna and Oxford-AstraZeneca both recommend a gap of four weeks, stretching to 12 weeks for the latter. Three weeks between doses are advised for the Pfizer-BioNTech vaccine and Gamaleya’s Sputnik V shot, while Sinopharm recommends between three and four weeks. The Sinovac jabs should be given two weeks apart.

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SCMP Explains: What's the difference between the major Covid-19 vaccines?

SCMP Explains: What's the difference between the major Covid-19 vaccines?

How effective are they?

The Pfizer-BioNTech vaccine has the highest efficacy rate of the six which are in distribution, at 95 per cent, closely followed by the Moderna shot, at 94.1 per cent, when the two shots are delivered within the recommended time frame.

Oxford-AstraZeneca says its vaccine, which has an overall rate of 70.4 per cent, is 90 per cent effective if given at half a dose, followed by a full dose. This drops to 62 per cent if delivered in two full doses, four weeks apart, but is still effective up to 12 weeks between doses, it says.

What do the Sinovac coronavirus vaccine efficacy results mean?

Sinopharm’s vaccine has been rated at 86 per cent efficacy by the United Arab Emirates health ministry, while the company’s own trials put it at 79.3 per cent.

Sinovac, the second Chinese company with an approved vaccine, hit a recent stumbling block in a Brazilian trial which found just 50.4 per cent efficacy. Separate trials of the vaccine in Indonesia and Turkey found it to be 65.3 per cent and 91.25 per cent effective, respectively.

Russia says its approved vaccine has a 91.4 per cent efficacy rate.

Efficacy of different vaccines cannot be compared directly because trial designs are different, but they are an important reference point for a vaccine’s effectiveness.

What are the side effects?

Vaccines work by training the body’s immune system to produce antibodies when it encounters the disease. Many side effects are common immune responses – some pain at the injection site, fever or chills, aches in joints and muscles, and a general feeling of being unwell. These typically last for several days, and not everyone will experience all of them.

Moderna has reported an additional potential side effect of swollen lymph nodes in the injection arm, as well as nausea and vomiting. Some of the vaccines include headache in their list of side effects.

Are they suitable for everyone?

The US Food and Drug Administration has approved the Pfizer-BioNTech vaccine for anyone aged over 16, while limiting the Moderna jab to 18 and older. In Britain, the Oxford-AstraZeneca vaccine has been declared suitable for those over 18.

The United Arab Emirates is administering Sinopharm’s vaccine to people aged 16 and over. The vaccine has not been cleared for use in minors in China, where provisions for the over-60s are also to be determined.

Indonesia has begun mass inoculations using Sinovac’s vaccine for people aged 18 to 59, while Turkey has prioritised vaccinations for the over-65s, also with Sinovac. Russia has approved the Gamaleya jab for people aged 18 and above.

Who is getting vaccines?

Many governments have placed orders for Covid-19 vaccines and most have also joined Covax, the WHO-led global initiative for fair distribution of inoculations.

In mid-January, WHO chief Tedros Adhanom Ghebreyesus warned of a “catastrophic moral failure” if vaccines were not shared and urged countries and manufacturers to ensure fair distribution around the world.

Rich nations have ordered 4.2 billion doses in direct deals with the suppliers, while countries in the higher middle-income bracket have secured 1.1 billion, according to the Launch and Scale Speedometer managed by Duke University’s Global Health Innovation Centre.

In comparison, lower middle-income countries have ordered 411 million doses, and low-middle income countries 270 million.

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Canada has bought enough doses to vaccinate its population five times over and has said it will donate the excess to poorer countries, while China has said it will make its vaccines available as a public good and is offering priority access and free doses to some developing countries.

Many wealthy nations have built diversified vaccine portfolios, according to a team from Johns Hopkins Bloomberg School of Public Health in the US. Their analysis, published in December, shows the US, Britain, European Union and Canada have each placed orders with at least six different manufacturers. Japan has struck deals with at least four suppliers, while Brazil has at least three.

What about poorer countries?

The pooled purchasing mechanism of Covax has secured almost 2 billion doses of several “promising” vaccine candidates, according to the WHO, which aims to cover up to 20 per cent of participants’ populations by the end of the year.

How many people need a Covid-19 vaccination to halt its spread?

Covax has signed up vaccine developers AstraZeneca/Oxford, Johnson & Johnson, Novavax, Sanofi/GSK and Pfizer-BioNTech.

The 190 countries taking part will have “access to doses in the first half of 2021, with first deliveries anticipated to begin in the first quarter of 2021”, according to the WHO.

Vaccine technologies

Conventional, so-called inactivated, vaccines work by exposing the body to a dead virus – which has been treated with heat, chemicals or radiation so it cannot infect cells and replicate – to trigger an immune response.

Viral vector vaccines use a harmless virus, called a vector, to deliver a small part of Covid-19’s genetic material into the body’s cells, which then replicates to trigger the immune response and the production of antibodies.

What are the coronavirus mRNA vaccines and how do they work?

The mRNA vaccines are a technological first. Scientists replicate the genetic instruction – the messenger ribonucleic acid (mRNA) strand – used by the virus to create its distinctive spike protein. The mRNA fragment is wrapped in a fatty parcel that dissolves after vaccination.

The vaccine enters the first body cells it encounters and instructs them to produce the artificial spike protein, triggering the immune system to attack the modified cells and destroy them, while retaining a memory of what to do if the threat is encountered again.

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