This is the level of protection you benefit from

• Millions of people around the world have been injected with two-dose COVID-19 vaccines.
• The Pfizer and Moderna vaccines are probably 80% effective against symptomatic COVID-19 after a dose.
• A single shot of AstraZeneca is probably at least 70% effective in preventing symptomatic COVID-19.
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More than 60 million Americans and more than 22 million Britons have received their first dose of a two-dose COVID-19 vaccine.

The United States has authorized the vaccines from Moderna and Pfizer-BioNTech, while the United Kingdom has authorized the vaccine from Pfizer as well as the one manufactured by AstraZeneca and the University of Oxford. The United States has also cleared Johnson & Johnson’s vaccine, which is a single dose.

The UK is delaying the second dose of vaccine for up to 12 weeks to prioritize the first injection. In the United States, the Centers for Disease Control and Prevention has recommended giving second doses of Pfizer vaccine 21 days after the first and 28 days after the first for Moderna, with an interval of up to six weeks in ” inevitable ”.

The data on how well vaccines work after a dose is unclear – it depends on what you are measuring and when you are measuring it. Stephen Evans, professor of medical statistics at the London School of Hygiene & Tropical Medicine and a former member of the Medicines Safety Committee at the European Medicines Agency, helped Insider break down the data.

Evans said the Food and Drug Administration’s submission of data from the late-stage trials was the best available data. This is the protection offered by one injection of each vaccine, based on this data.

Pfizer-BioNTech: at least 80%

Pfizer’s injection was 52.4% effective in protecting against COVID-19 with symptoms between the first and second dose, according to FDA documents. But the 52.4% figure includes the 11 days before protection starts after the first dose, so the actual percentage may well be higher.

The true value is between 29.5% and 84.5%, according to FDA documents. There was a wide range as not many people got COVID-19 from testing during that time.

Professor Stephen Evans

The Pfizer injection was 100% effective in protecting against hospitalization and death. This was based on a small number however – only four people had severe COVID-19 in the trial after receiving a placebo rather than the vaccine.

Evans said there was “pretty clear evidence” that you get at least 80% protection – and “probably” better than 90% – for Pfizer’s COVID-19 vaccine with symptoms after just one dose. He said you couldn’t be absolutely sure what happened after 21 days because it hadn’t been fully tested.

Evans said this was based on his overall reading of the test data used by the FDA in their pre-clearance brief.

Moderna: at least 80%

Moderna’s vaccine was 69.5% effective at preventing COVID-19 with symptoms between the first and second dose, with an actual value between 43.5% and 84.5%. The range was quite wide as the number of people who contracted COVID-19 from the test during this time was small.

The 69.5% figure includes the 13 days before coverage begins, so the actual percentage may be higher.

There were a small number of people in the Moderna trial – around 7% – who did not receive their second dose for unknown reasons. In this group, the vaccine was 50.8% effective at preventing COVID-19 with symptoms for up to 14 days after the first dose and 92.1% after 14 days.

It is not known how well an injection of the vaccine protects against hospitalization and death, as few people have contracted severe COVID-19 – two in the vaccine group and four in the placebo group.

Evans said you have at least 80% – and probably better than 90% – protection for Moderna’s COVID-19 vaccine with symptoms after a single dose for 28 days. After 28 days it was not clear as he had not been tested. Again, this was based on his overall reading of FDA data, he said.

AstraZeneca: over 70%

Evans said it was more difficult to come up with a figure for AstraZeneca’s vaccine because the late-stage trials used different study designs and a large US study was underway.

The FDA has also not yet presented the data for the vaccine in the same way it has for other vaccines.

A single dose of AstraZeneca injection was 76% effective in protecting against COVID-19 with symptoms for at least 90 days, according to data from advanced stage trials published in The Lancet on February 19. % protection from hospitalization, but the numbers were low.

Based on his reading of existing studies, Evans said the single-dose effectiveness of AstraZeneca’s vaccine was likely at least 70% against COVID-19 with symptoms for the first 90 days. After this period, it is not clear, he said.

Johnson and Johnson: 66%

J&J has looked at protection against moderate to severe COVID-19 in trials, rather than symptomatic COVID-19, like Pfizer, Moderna and AstraZeneca.

Protection started at 14 days and was 66.1% effective at 28 days. The vaccine’s effectiveness varied depending on the country in which it was used – it was 72% effective in the United States but 64% and 68% in South Africa and Brazil, respectively. These countries both have circulating coronavirus variants that could partially escape antibodies.

What does the percentage of efficiency mean?

Vaccine efficacy percentage refers to the proportion of people who are fully protected after a vaccine. With an efficiency of 80%, 80% of people benefit from full protection and 20% do not.

For those who get full protection the first time around, the second hit improves the quality of the immune response and its durability.

For people who do not get full protection with the first injection, some will get full protection after the second dose. Some people will never get full protection from a vaccine because their immune system does not respond at all.