How do the three Covid 19 vaccines compare?

The increasing Covid 19 vaccine supply

The Johnson and Johnson Covid 19 vaccine is finally available.

I have been receiving questions about how safe and effective it is compared to the Pfizer and Moderna vaccines. So here is a succinct summary that I hope will be helpful to you.

Number of Vaccine Shots Required

  • Pfizer vaccine – 2 shots – 21 days apart (although they can be up to 42 days apart if the vaccine is hard to get)
  • Moderna vaccine – 2 shots – 28 days apart
  • J&J vaccine – 1 shot only (J&J is currently testing the effect of a booster shot on antibody levels)

Efficacy of the Covid 19 vaccine shots

  • Pfizer vaccine – after the required 2 doses – prevents 95% of symptomatic Covid infections across age groups and racial and ethnic groups (tested 7 days after last dose)
  • Moderna vaccine – after the required 2 doses – is 94% effective at preventing symptomatic Covid infections (tested 14 days after last dose)
  • J&J vaccine – after the single required dose – is 85% protective against severe Covid illness. A severe Covid illness is defined by J&J as a combination of a positive test and at least one symptom such as shortness of breath. (This was tested for both 14 and 28 days after dose). It is between 66%-72% protective against moderate/severe infections (tested 28 days after dose)

Note – It is important to remember that most viral vaccines are considered acceptable if effective over 50%. For reference purposes the flu vaccine is around 60% effective.

Genetic Vaccine Components

  • Pfizer and Moderna vaccines- use mRNA single strand genetic instructions. This means the vaccine content doesn’t have to enter the nucleus of a cell to be turned into the needed viral ‘spike’ protein. The vaccine material never mixes with our own DNA. It is carried to the cell inside a nano-sized membrane sphere (not alive), and released to the protein factories in the cytoplasm
  • J & J vaccine – uses double stranded DNA genetic instructions, which are carried into the cells by an often-used-in-medical-labs adeno virus. The DNA is injected into the cell by the carrier virus and then must first enter the nucleus (amongst our own DNA). There it is turned into the single strand mRNA, and sent outside the nucleus to the protein factories in the cell.

Note – No Covid infection is possible from any of the vaccines!

Note – No adenovirus infections occur with the J & J vaccine. They have been stripped of their ability to reproduce.

Safety of the Covid 19 Vaccines

The Pfizer and Moderna vaccines mainly have mild local and body effects with the first dose. With the second dose, up to 15% of people may have more noticeable body effects, like headaches, muscle aches, fever lasting several days. This can be uncomfortable in a flu-like way, but it is a good sign that the immune system is developing well. In fact younger people are more likely to notice these effects because their immune systems are stronger than those of older people.

Allergic reactions are low because these mRNA vaccines do not contain the egg or latex allergens. See this Moderna Fact sheet for details of what they do contain.

Anaphylaxis (a severe immune response) is possible with both vaccines, but is very uncommon. It occurs in only 4 out of 1 million doses for Pfizer, and about 2 out of 1 million doses for Moderna. They usually occur within the first 15-30 minutes after a shot, which is why all receivers of the vaccine are kept under observation for 15 minutes before being allowed to leave. They occur more often in people who have severe allergies or have had anaphylactic reactions before.

The J&J vaccine may provide both local and systemic effects in the day or so following the one dose (it is a larger dose than the individual doses of the other two vaccines), but also seems very safe. So far only one recorded anaphylaxis reaction has been noted. See this J&J Fact sheet for details of what is contained in the vaccine.

Storage of Vaccines

The mRNA vaccines (Pfizer and Moderna) require careful cold storage which has been a definite limiting factor in vaccination procedures.

  • Pfizer has recently announced that its vaccines can be shipped and stored (for a 2 week period) in normal pharmacy freezers (-13 to 5 degrees F), which is a big improvement.
  • Moderna’s must be shipped and stored at -4 degrees F (within regular refrigerator freezer temperatures).
  • On the other hand, J&J’s vaccine can be stored at least 3 months at regular refrigerator temperatures, and 12 hours at room temperature. This makes it by far the easiest vaccine to distribute.

Durability of Vaccine Protection

How long our protective antibodies will last, and when/if we’ll have to get boosters is currently unknown for each of the three vaccines. All vaccine producers are working on boosters.

Vaccine Protection from Virus Transmission

Although the vaccines all protect us from severe symptoms of the Covid 19 illness, it is not known how well any of the vaccines prevent us having asymptomatic infections and transmitting the virus to others. This is why vaccinated people should keep wearing masks and social distancing until further studies give us the answers we need.

Vaccine Protection against Variants of the Covid 19 Virus

Variants of the original vaccine arise because the SARS-CoV-2 virus (Covid 19) is an RNA virus. These viruses change much more rapidly than the common DNA viruses. Every time they make a copy of their genes they make one or a few mistakes. And they copy themselves many, many times in every sick body!

These mistakes are called mutations, and sooner or later a mutation helps the virus in some way. Perhaps they can link up to the host’s cells more strongly. Perhaps they can invade the cells more quickly. Or perhaps they are better at hiding from the immune cells. With such an advantage they can reproduce more quickly than the other virus cells, and soon a ‘new variant’ appears.

The effectiveness of the 3 vaccines has not been particularly challenged by the U.K. variant but they have all noted some drop of effectiveness against the S. African variant, with the J&J vaccine dropping the lowest. However so far they all maintain good protection against severe disease.

The vaccine-producing companies are continually monitoring the type of Covid 19 found in new infections with an eye to modifying the vaccines if new mutations extend past the vaccine’s effectiveness. Moderna is already considering changes to the second dose.

Use in pregnant women

The American College of Obstetricians and Gynecologists (ACOG) and the CDC both recommend making any of the three vaccines available to pregnant and lactating women who fit within the risk category currently being vaccinated. At the same time they encourage them to talk with their health provider. Meantime Pfizer and Johnson&Johnson are currently conducting trials involving pregnant women.

Note – Neither previous animal testing, nor pregnancies occurring within vaccination trials indicate raised risks.

Use in children

At this time, the Pfizer-BioNTech vaccine is authorized for ages 16 and up, and the Moderna and Johnson & Johnson vaccines are authorized for ages 18 and up. There are no immunizations available from any of the companies at present for children under 16.

Trials have been going on since December in both Moderna and Pfizer involving adolescents ages 12- 18, and vaccines for that age group may be available sometime in the summer. Whether they will be widely available before the fall is uncertain.

Younger children – “The CDC’s Advisory Committee on Immunization Practices (ACIP) meets regularly to provide updates on a variety of vaccine-related issues, but for months now, there has been a call for the need for pediatric COVID-19 vaccine trials. Moderna has begun testing its vaccine in children ranging from 6 months of age to 12 years old. Pfizer-BioNTech also has vaccine trials that are currently being performed in adolescents. Johnson & Johnson is expected to follow suit, and trial investigators have already begun with the Oxford-AstraZeneca vaccine in children 6 years and older“. HCP Live

However it is likely that no younger children’s vaccines will be available for the Fall 2021 semester. The body weight and immune system in a child 6 months old varies enormously from that of a 5 year old, which in turn varies a lot from that of a 12 year old. All of which means that the dosage safety testing will take longer in children than it did in both adolescent and adult groups, who are much more similar to each other.

Vaccine makers usually work from the oldest children down to the youngest, so vaccines will probably be available in the 10-12 age range first.

Were any of the vaccines produced using embryonic stem cells?

See my answer in this post

The bottom line?

The three vaccines are similarly safe, and protective against severe Covid 19 disease. They also share the same currently unknown features. I will keep you updated about those features as more becomes known

So while vaccines are still in short supply I would encourage you to take the first one that becomes available to you.

Let me know if you have further questions.


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