COVID-19 vaccines: Safety, side effects –– and coincidence – Harvard Health Blog

As the pandemic rages on, it is increasingly clear that widespread vaccination is essential to help contain it. Physical distancing, universal face coverings, and frequent hand washing are effective, but not foolproof. And of course, these metrics don’t work if they’re not followed.

So the rapid development of mRNA vaccines and other vaccines to prevent COVID-19 is welcome – some say miraculous – news. But while many people are scrambling to get vaccinated, others are hesitant.

Start here: Are these vaccines safe and effective?

It is natural to wonder whether new vaccines against a novel coronavirus, being developed at an unprecedented speed, are effective and safe to take. Let’s go over some of what we know.

Overall efficacy has been reported in a range of 70% to 95%. That’s well above the average effectiveness of the flu shot, for example.

  • A Pfizer / BioNTech vaccine trial involving nearly 44,000 volunteers found the vaccination to be 95% effective. This vaccine is authorized in the United States.
  • A Moderna vaccine trial recruiting more than 30,000 volunteers reported an efficacy of 94%. This vaccine is authorized in the United States.
  • An AstraZeneca / Oxford vaccine trial reported an average efficacy of 70% with full doses, but even better results (up to 90%) with a lower dose. This vaccine is authorized for use in Great Britain, but not in the United States.
  • In a press release, Johnson and Johnson announced an overall effectiveness of 66% in preventing moderate to severe COVID-19. The company has applied for emergency use authorization in the United States.

Not only do these vaccines appear to reduce the risk of developing COVID-19, but they also appear to reduce the risk of serious illness.

What are the most common side effects of the COVID vaccine?

In large clinical trials, most side effects have been minor. When side effects do occur, they usually only last a few days. A side effect or reaction isn’t necessarily all bad, by the way; this may indicate that the body is building protection against the virus.

For the four vaccines listed above, common side effects include

  • pain at the injection site
  • painful and swollen lymph nodes in the arm where the vaccine was injected
  • tired
  • headache
  • muscle or joint pain
  • nausea and vomiting
  • fever or chills.

What else should I know about possible side effects?

  • Severe allergic reactions. In rare cases, a life-threatening reaction called anaphylaxis can occur, most often in people known to have had severe vaccine reactions in the past. CDC estimates suggest that anaphylaxis occurs in 11 cases per million doses in people receiving the Pfizer / BioNTech vaccine. The signs are difficulty in breathing, swelling of the face and throat, rash, and low blood pressure. It usually occurs soon after vaccination and can be treated with epinephrine (like in an EpiPen). That is why people are observed for at least 15 minutes after receiving the vaccine with epinephrine on hand.
  • Unexplained deaths. A recent report of 23 deaths among older people vaccinated in Norway has raised understandable safety concerns about new COVID-19 vaccines. However, further investigation is needed to determine whether these deaths were vaccine-related or represent an expected number of deaths among frail people who may already have limited life expectancies.

Reject two misconceptions about vaccines

It is normal to feel cautious about any new treatment. But two common misconceptions can encourage people to avoid getting the COVID vaccine.

  • Health problems wrongly attributed to the vaccine. When health problems arise soon after vaccination, people tend to blame the vaccine. Yet cancer, strokes, heart attacks, blood disorders and rare diseases happened before the pandemic and of course will continue to happen. Many people are expected to develop such health problems whether or not they are vaccinated. If a thorough investigation shows that certain health problems are occurring at a higher than normal rate, the vaccine could be to blame. Otherwise, it’s more likely to be an unfortunate coincidence that is unrelated to the vaccine.

    For example, rare cases of Bell’s palsy and other neurological diseases have been reported after COVID vaccination. But so far, there is no clear indication that the vaccine has played a role. Likewise, a fatal blood disease suffered by a doctor in Florida two weeks after receiving a COVID-19 vaccine has raised concerns that it was triggered by the vaccine. This condition did not occur among the tens of thousands of subjects in clinical trials, so it could be a complete coincidence. Authorities are investigating this case.

  • Concern that the vaccine could cause COVID-19. This cannot happen because no live SARS-CoV-2 virus is used in vaccines currently available or in development. If a person develops COVID-19 soon after being vaccinated, it is not due to the vaccine. This is either because the vaccine failed (which is rather rare) or because an infection developed before the vaccine had a chance to work. In fact, some people may already be infected with the virus at the time of vaccination.

The bottom line

So far, we know COVID-19 is an unpredictable and potentially fatal disease. And the information we have on the effectiveness and safety of COVID-19 vaccinations is encouraging. Minor side effects should be expected; severe allergic reactions may rarely occur. Side effects of the vaccine are not reasons for most people to avoid vaccination.

As the number of people vaccinated and the number of different vaccines increase, vigilance is called for. What we know today about side effects and safety will not be the last word. Volunteers participating in clinical trials and members of the public who have been vaccinated continue to be monitored and are encouraged to report issues.

There are advantages and disadvantages to any new medical treatment. But remember that there are also pros and cons to in decline treatment. From my reading of the information currently available, the decision to get vaccinated against COVID-19 should be easy.

Follow me on twitter @RobShmerling

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Jothi Venkat

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