Vaccines: What does X percent effective mean?

The effectiveness that the manufacturers claim for their vaccines have a wide range and some may protect better than the numbers suggest. So what is the story behind these numbers?

95% effectiveness, 80% effectiveness or just 60% effectiveness? The information about the newly developed coronavirus vaccines makes many people aware that vaccinations have different effects – and that no vaccination offers 100% protection.

In the case of immunisations against flu, measles or polio, little thought has been given to this topic so far – usually only one vaccine is available for this anyway. On the other hand, the efficacies that are certified for the various coronavirus vaccines are now being discussed.

Initial groups getting the shots prefer not to be vaccinated with the “less effective” vaccines from AstraZeneca or later Johnson & Johnson, but is the difference really as big as the numbers suggest?

covid-19 vaccine effective

Efficacy against disease

To test the effectiveness of a vaccine, large phase III studies compare how many participants get the disease without and how many despite the vaccine. The sick include anyone who developed symptoms, even if it is just a temporary cough.

With the new coronavirus vaccines, for example, it looked like this: of 100 test subjects who developed symptoms, only 5 or 6 were in the vaccination group for the mRNA vaccines from BioNTech and Moderna, the remaining 95 and 94 in the vaccine group study, who became infected, were not vaccinated (so 95% and 94 % effectiveness).

With the AstraZeneca vector vaccine, these values ​​were closer together: of the participants who developed symptoms, 40% were vaccinated and 60% were not vaccinated (so 60% percent effectiveness). With the vector-based vaccine from Johnson & Johnson, the ratio should be slightly better at 34 versus 66 (so 66% effectiveness).

Compared to the mRNA vaccines, the vector virus vaccines appear to be less effective. But you have to know that it has already been determined in advance that 50% effectiveness is to be rated as a success.

Above all, in all studies on the vaccines approved so far, there was no person who was seriously ill among the vaccinated. And that is the real good news. Even the less effective vaccines are still extremely effective at protecting against severe disease. And that was initially the main goal of the vaccinations against Sars-CoV-2.

Effectiveness against infection

Another form of effectiveness describes how well a vaccine protects not only against the onset of a disease, but also against infection. Doctors call this “sterile immunity”. If this is guaranteed, it means that as a vaccinated person you cannot infect anyone else.

This is the case, for example, with the combination vaccine against mumps, measles and rubella (MMR). It effectively protects not only the vaccinated person, but also those around them and thus increases herd immunity.

With the coronavirus vaccines, however, at this point it is still unclear. Experts suspect that the vaccines may not completely prevent infection, but could significantly reduce the likelihood of passing the virus on. That too would make a major contribution to containing the pandemic.

Effectiveness against mutants

All viruses mutate continuously – with the flu virus, for example, it happens so quickly and extensively that manufacturers have to mix up a new vaccine every year. This then protects against the most common of the currently circulating flu virus types, but not all, but this is not a problem. All previous infections with previous flu viruses ensure the body a kind of basic immunity against the diverse pathogens.

For this reason, adults and older children are much less likely to develop influenza than younger children. Because you have come into contact with flu viruses many times in your life. Your immune memory therefore also reacts to new flu viruses, albeit less than to “old friends”.

Sars-CoV-2 is also constantly changing – albeit much more slowly than flu viruses. In addition, most mutations play no role in the infection or the vaccine effect – they change gene segments of the virus that the vaccine does not target.

However, some vaccines against current or future mutations could actually lose their effectiveness. At least the AstraZeneca vaccine in South Africa, where variant B.1.351 has spread widely, seems to be less protective.

But that does not mean that the vaccine has no protective effect against the mutant. For example, it could at least prevent severe disease progression. Whether this is actually the case and how well the vaccines works against the various mutations is still open.

This also applies to the mRNA vaccines from BionTech / Pfizer and Moderna. However, these initial studies seem to work unabated against the British mutation.

What’s the best Covid-19 Vaccine?

There is huge demand for vaccines from the planet’s 7.8 billion inhabitants. So, if a vaccine requires two doses, that is a lot of vials that need to be produced, preserved and delivered. Even so, more vaccines may be needed, as some will inevitably spoil during transport or handling. For now, there are a few key questions on everyone’s mind: Which is the best COVID-19 vaccine? What is available now? Fortunately, there are numerous options at humanity’s disposal.

What vaccine efficacy rate would you accept for yourself? The World Health Organisation (WHO) and most health regulators agree on this: a 50% efficacy rate for a new vaccine is the “acceptable” threshold and the good news is that by this reckoning many trials that have been conducted around the world have posted incredibly high success. Moreover, new ways of developing vaccines (such as mRNA) have been found. The utility of tried-and-tested platforms (inactivated/attenuated vaccines) had been re-affirmed. In the United Arab Emirates (UAE), there are currently four approved vaccines: Sinopharm (December 9, 2020), Pfizer-BioNTech (December 23, 2020), Sputnik V vaccine (January 21, 2021), and AstraZeneca (approved in Dubai on February 2, 2021).

Whether you have the most expensive private health insurance or are reliant on the free vaccines being provided by most governments, choices are limited. There are currently not enough to go round and most people, if they can get access to a vaccine, will not be able to choose which one. So with so many vaccines out there and with such a range of reported efficacy figures is one better than another? Should we wait for a specific one? Or will they all help sufficiently such that we should take whichever one is made available to use. The following list shows a number of vaccines against SARS-CoV-2 that all took less than 12 months to be made available to the public.

  1. Pfizer-BioNTech – It is an mRNA vaccine that codes for the virus’s spike protein and is encapsulated in a lipid nanoparticle. Once injected, the cells churn out the spike protein, triggering the body’s immune system to recognise the virus. In Phase III trials, it demonstrated 95% efficacy. The Pfizer-BioNTech vaccine requires storage at about -94 degrees F, which requires specialised freezers.
  • Type: mRNA
  • Doses: 2, 21 days apart.
  • Efficacy: About 95%
  • Variants: Lab data suggest “quite effective” against the UK variant as well as the South African and Latin American variants.
  1. Moderna – Like the Pfizer-BioNTech vaccine, it is an mRNA vaccine. Unlike that vaccine, however, the Moderna vaccine is stable at 36 to 46 degrees F, about the temperature of a standard home or medical refrigerator, for up to 30 days and can be stored for up to six months at -4 degrees F.
  • Type: mRNA
  • Doses: 2, 28 days apart.
  • Efficacy: About 95%
  • Variants: Lab data suggest “quite effective” against the UK variant as well as the South African and Latin American variants.
  1. AstraZeneca – University of Oxford – The AstraZeneca and University of Oxford’s vaccine uses technology from an Oxford spinout company, Vaccitech. It deploys a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees. It contains the genetic materials of the spike protein. After vaccination, the cells produce the spike protein, stimulating the immune system to attack the SARS-CoV-2 virus. The AstraZeneca vaccine can be stored, transported and handled at normal refrigerated conditions, about 36-46 degrees F for at least six months and administered within existing healthcare settings.
  • Type: Adenovirus-based
  • Doses: 2, 28 days apart.
  • Efficacy: Currently about 70% overall
  • Variants: At least one study finds it has little effect against the South African variant, but appears effective against UK and Brazilian variants.
  1. Johnson & Johnson – The vaccine uses the company’s AdVac technology platform, which it used to develop its approved Ebola vaccine and its Zika, RSV and HIV investigational vaccine candidates. It revolves around the use of an inactivated common cold virus, similar to what the AstraZeneca-University of Oxford program utilises. All of the other three vaccine candidates require two doses about 28 days apart, the J&J vaccine only requires a single dose.
  • Type: Adenovirus-based
  • Doses: 1
  • Efficacy: Currently about 66% overall
  • Variants: Based on clinical studies in Africa, UK and Latin America, there is evidence the vaccine is effective against the variants, although less so against the South African and Latin American strains.
  1. Russia’s Sputnik V Vaccine – The Sputnik vaccine works in a similar way to the Oxford/AstraZeneca jab developed in the UK, and the Janssen vaccine developed in Belgium. It uses a cold-type virus, engineered to be harmless, as a carrier to deliver a small fragment of the coronavirus to the body. Safely exposing the body to part of the virus’s genetic code in this way allows it to recognise the threat and learn to fight it off, without risking becoming ill. After being vaccinated, the body starts to produce antibodies specially tailored to the coronavirus. This means the immune system is primed to fight coronavirus when if it encounters it for real.
  • Type: Adenovirus-based
  • Doses: 2
  • Efficacy: 91.4%
  • Variants: Unknown. Clinical trial data was largely conducted in Russia prior to the emergence of major variants.
  1. Sinovac Biotech – China-based Sinovac Biotech reported that its COVID-19 vaccine had a 50.4% efficacy in late-stage clinical trials in Brazil. The company’s clinical trials are demonstrating dramatically varying efficacy rates. In Indonesia, a local trial demonstrated an efficacy rate of 65%, but the trial had only 1,620 participants. Turkey reported an efficacy rate of 91.2% in December 2020. Another trial in Brazil run by a local partner, Butantan Institute, reported a 78% efficacy rate in mild cases while 100% against severe and moderate infections. It is an inactivated vaccine that uses inactivated SARS-CoV-2 viruses.
  • Type: Inactivated SARS-CoV-2 virus
  • Doses: 2
  • Efficacy: 50.4% to 91.2%, depending on the clinical trial
  • Variants: Unknown, although a study in Brazil demonstrated 50.4% efficacy at preventing symptomatic infections.
  1. Novavax – The vaccine is a protein-based COVID-19 vaccine candidate. The vaccine contains a full-length, prefusion spike protein made using the company’s recombinant nanoparticle technology and its proprietary saponin-based Matrix-M adjuvant. It is stable at 2 to 8 degrees C and shipped in a ready-to-use liquid formulation.
  • Type: Protein-based vaccine
  • Doses: 2
  • Efficacy: 89.3%
  • Variants: Effective against UK and South African
  1. Sinopharm – China-based Beijing Institute of Biological Products Co. Ltd was first tested outside China in the United Arab Emirates from where it was reported to have 86% efficacy. The UAE authorities have later gone on to state that the vaccine is 100% effective at prevent severe illness in infected people. Although one of the most available and used vaccines in the world, and one that has been approved for use in a growing number of countries, data has reportedly not been as forth coming for international peer review and consequently international approval as it has for other products. Hungary is currently the only western country to have approved its use. It is an inactivated vaccine that uses inactivated SARS-CoV-2 viruses.
  • Type: Inactivated SARS-CoV-2 virus
  • Doses: 2
  • Efficacy: 86% as per the UAE clinical trial
  • Variants: Unknown, as there is no publicly available data to review although it is expected to retain a degree of effectiveness like other vaccines.