How Protected Are You After Getting Your First Vaccine?

Around the world, millions of people have had one shot of two-dose COVID-19 vaccines. In America, more than 147 million Americans have received their first dose. Moreover, in the UK, more than 34 million Britons have gotten their first dose.

The FDA in the US has approved the use of Moderna and Pfizer-BioNTech vaccines. On the other hand, the UK has authorized Pfizer’s shot and another one made by AstraZeneca and Oxford University. Moreover, Johnson & Johnson’s vaccine is also allowed in the US. It is a single-dose vaccine.

The main question is; how much protection does one get from these vaccines? Let’s find out.

Science alert, in a recent post, discusses the power of vaccines.

Vaccine Dose

The UK has decided to delay the second dose of coronavirus vaccines. Between the first and second dose, there is an interval of up to 12 weeks. This strategy prioritizes giving people their first shot.

The Centers for Disease Control and Prevention has made recommendations for giving second vaccine doses in the US. After the first dose of Pfizer’s vaccine, people should receive their second one after 21 days. 

Also, 28 days after the first dose of Moderna, people should receive the second one.

Best Data

When it comes to the performance of the first dose of the vaccine, the data is not always clear-cut. It all depends on when you measure and what you are measuring.

Stephen Evans helped break down the data. Evans works at the London School of Hygiene & Tropical Medicine. He is a professor of medical statistics Additionally, he was a drug-safety committee member at the European Medicines Agency.

He said that the best data available was in the presentation of the Food and Drug Administration. They gathered the data from late-stage trials of each vaccine. It tells us how much protection one shot of each vaccine gives us.


At protecting against COVID-19, Pfizer’s shot was 52.4 percent effective. According to the FDA documents, with symptoms between the first and second dose. However, this figure includes the 11 days following the first dose, after which the protection kicks in.

It means that the actual percentage could be higher. According to the FDA documents, the true value lies between 29.5 percent and 84.5 percent. It is a wide range because not many people in the trial during this period caught COVID-19.

Clear Evidence

At protecting against hospitalization and death, Pfizer’s shot was 100 percent effective. This conclusion was based on a small number because only four people got severe COVID-19 in the trial. It happened after they received a placebo rather than the vaccine.

According to Evans, there was clear evidence that the protection you get is at least 80 percent. Also, it is seemingly better than 90 percent for Pfizer’s vaccine against symptomatic COVID-19 after one dose.


At preventing COVID-19 with symptoms between the first and second dose, Moderna’s vaccine was 69.5 percent effective. According to the documents, the true value lies between 43.5 percent and 84.5 percent.

During this period in the trial, the number of people that caught COVID-19 was low. The actual percentage could be higher because this figure includes the 13 days before protection starts.

Experimental Group

For unknown reasons, a small number of people- about 7 percent did not get their second dose. The shot was 50.8 percent effective at preventing COVID-19 in this group for up to 14 days. Also, after 14 days, it was 92.1 percent effective.

The protecting power of one-shot of the vaccine against hospitalization and death is unclear. In this group, not many people got severe COVID-19. Only two people in the vaccine group and four in the placebo got affected.


According to Evans, for AstraZeneca’s vaccine, it was harder to determine a figure. In the late-stage trials, the researchers used different study designs. Also, a large US study was ongoing.

Furthermore, in the past, the FDA has exhibited information for vaccines. However, for this shot, the data is yet to be presented.

The Efficiency

For at least 90 days at protecting against COVID-19 with symptoms, AstraZeneca’s shot was 76 percent effective. On February 19 in The Lancet, the late-stage trial data got published.

Moreover, the study authors reported that against hospitalization, one dose provided 100 percent protection. However, the numbers were small.

Evan said that the efficiency of the AstraZeneca vaccine’s single dose was probably at least 70 percent for the first 90 days. It is unclear after this period, he said.

Johnson & Johnson

Rather than looking at symptomatic COVID-19, J&J looked at protection against moderate to severe COVID-19 in trials.

At 14 days, the protection kicked in. Also, at 28 days, it was 66.1 percent effective. Also, the effectiveness of the vaccine varied according to the country. For instance, in the US, it was 72 percent effective. However, in South Africa and Brazil, it was 64 percent and 68 percent effective, respectively.

Both of these countries have coronavirus variants circulating. They could evade antibodies partially.

Newest Information

Public-health authority in England on May 23 published new data. According to it, Pfizer and AstraZeneca vaccines worked better when two doses were given rather than one.

Against symptomatic COVID-19 caused by the variants, both vaccines were 30 percent effective. Three weeks after the first dose, it got identified in India.

Two weeks after the second dose, the effectiveness increased between 60 percent and 88 percent. Three weeks after the first dose, the two vaccines were 50 percent effective against symptomatic COVID-19 against the variant first found in the UK.

Two weeks after the second dose, it increased to between 66 percent and 93 percent.

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Millions of people around the world have received one shot of two-dose COVID-19 vaccines. There are several vaccines out there. However, the US has approved vaccines from Moderna and Pfizer-BioNTech. Also, the UK has authorized Pfizer’s shot and one made by AstraZeneca and Oxford University.

Moreover, the UK also approved Johnson & Johnson’s vaccine, which is a single dose. The effectiveness of these vaccines differs from each other.

Against symptomatic COVID-19 after one dose, the Pfizer and Moderna vaccines are likely 80% effective. Also, at preventing symptomatic COVID-19, a single AstraZeneca shot is probably at least 70% effective. Moreover, the Johnson & Johnson vaccine is at least 66% effective.

According to data, one dose significantly reduces infections and transmission. Also, the second dose provides better protection against variants.

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