5 things to know after you’ve had a COVID-19 vaccine
As more and more people get vaccinated against COVID-19, some are worrying about how ‘normal’ their side effects are. Here’s what you need to know.
- 29 March 2021
- 3 min read
- by Priya Joi
1. Influenza-like illness
The WHO Global Advisory Committee on Vaccine Safety investigated reports of a influenza-like illness following COVID-19 vaccination, included symptoms such as headache, fatigue, muscle aches, feverishness and chills. In their report on 8 March, they found that most symptoms were mild to moderate and resolved within a few days. They also noted that these were expected side effects from this type of vaccine, and that these symptoms are more common in people younger than 55 compared with older people. The committee emphasised that the benefits of the vaccines outweighed any risks, and that even people who had influenza-like illness should still get their second dose.
2. Women are more likely to have side effects
In a study last month, researchers at the US Centers for Disease Control and Prevention (CDC) analysed data collected after the first 13.7 million COVID-19 vaccine doses were given in the USA. They found that 79.1 percent of reported mild side effects came from women, even though women had been given only 61.2 percent of the vaccines. This seems consistent with previous findings that women are more likely to have mild side effects from vaccines. The same study reported that no serious safety problems were reported.
The risk-benefit ratio is critical for any vaccine, and because COVID-19 transmission is still dangerously high in much of the world, these relatively minor side-effects are still far outweighed by the benefits of taking the vaccine.
3. Women are also likely to have a stronger immune response
Heightened side effects in women seems to correlate with the development of greater levels of antibodies (potentially twice as many than men) after vaccines for flu, MMR, yellow fever, and hepatitis A and B. One reason could be that that sex hormones including estrogen, progesterone and testosterone can bind to immune cells and affect how they work. Estrogen can boost antibody levels, whereas testosterone can be suppressive.
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4. Countries will keep monitoring side effects
The WHO recommends that all countries should continue to monitor vaccine safety and data on suspected adverse events. This should be reviewed continuously at national, regional and global levels as COVID-19 vaccines are rolled out worldwide to ensure they are continuing to provide a positive benefit-risk balance.
5. Protection against disease, and potentially against transmission
The risk-benefit ratio is critical for any vaccine and, because COVID-19 transmission is still dangerously high in much of the world, these relatively minor side-effects are still far outweighed by the benefits of taking the vaccine. Now, it looks like the vaccines could also reduce transmission of at least some variants of SARS-CoV-2, the virus that causes Covid-19. For example, a recent study from the UK reported that the Pfizer/BioNTech vaccine seems to cut transmission by 86-90% seven days after the second dose, and just one dose of the Moderna vaccine could reduce transmission by 61%.