Side Effects From mRNA Covid Vaccines Usually Mild And Temporary, Large US Study Finds

For more than 298 million vaccine doses administered between December 2020 and June 2021, 92 per cent of reported adverse events were not serious, according to a new study.

New Delhi: A review of adverse events which take place after vaccination against Covid-19 with mRNA vaccines in the United States confirms that most side effects were mild and decreased substantially after one day, according to a new study published in the The Lancet Infectious Diseases journal. For more than 298 million vaccine doses administered between December 2020 and June 2021, 92 per cent of reported adverse events were not serious, the study suggests. 

What Is v-safe?

Also, less than one per cent of v-safe participants reported seeking any medical care following vaccination. According to the Centers for Disease Control and Prevention (CDC), v-safe provides personalised and confidential health check-ins via text messages and web surveys so that one can quickly and easily share with the CDC how they, or those dependent on them, feel after getting a Covid-19 vaccine. With this information, the CDC can monitor the safety of Covid-19 vaccines in real time. The v-safe system consists of smartphone-based surveys sent daily for the first week after vaccination, and also at longer time intervals in the months following, to monitor adverse reactions.

What Were The Most Commonly Reported Adverse Events?

Pfizer BioNTech and Moderna are two mRNA Covid-19 vaccines which were authorised for emergency use in the US, in December 2020. These vaccines, which involve two primary doses, have shown good safety profiles in clinical trials. Moreover, mild effects such as injection site pain, fatigue, and headache were reported as the most common adverse events. 

What Is VAERS?

People living in the US can report adverse events occurring after vaccination, using the Vaccine Adverse Event Reporting System (VAERS). This is a long-standing reporting system run jointly by the CDC and the US Food and Drug Administration (FDA). Residents of the US, their healthcare providers, or vaccine manufacturers can submit any event experienced following receipt of a vaccination, using VAERS.

Quoting Dr Hannah Rosenblum from the CDC, a statement issued by The Lancet said that vaccines are the most effective tool to prevent serious Covid-19 disease outcomes and the benefits of immunisation in preventing serious illness and death strongly favour vaccination. She further said that Covid-19 vaccine safety monitoring is the most robust in US history and that the two complementary surveillance systems used in this study should bolster confidence that mRNA Covid-19 vaccines are safe. 

The researchers analysed available VAERS and v-safe self-reported data between December 2020 and June 2021 following both doses of either the Pfizer-BioNTech or Moderna mRNA vaccines, according to the study. Over 298 million doses of mRNA vaccines were administered during the study period. These included 132 million doses of Moderna vaccine and 167 million doses of Pfizer vaccine. 

How Many Cases Of Adverse Events Were Reported?

Over 3,40,000 cases of adverse events were reported using VAERS. More than 3,13,000 cases were registered as non-serious. These accounted for 92 per cent of the reports, and included adverse events such as headache, fever, fatigue, chills, and pain, according to the study.

How Many Cases Were Registered As Non-Serious?

More than 22,000 side effects were registered as non-serious, and accounted for 6.6 per cent of the reports. Of these, the most common was shortness of breath. 

As many as 3,40,522 adverse events were reported to VAERS during the study period. Of these, approximately 4,500 were deaths. 

More Than 80% Deaths Reported In Participants Aged 60 & Above

More than 80 per cent of these deaths were reported among people aged 60 years or older, according to the study. Healthcare providers are required to report all deaths following vaccination, regardless of the potential direct association. This is because Covid-19 vaccines have been authorised under emergency use. Also, no unusual patterns were detected in cause of death reports.

Quoting Dr David Shay from the CDC, the statement said that the rapid pace at which Covid-19 vaccines were administered under emergency use, especially among older populations, was unprecedented. He said that due to their age, this group already has a higher baseline mortality rate than the general population. He further said that the researchers’ results follow similar patterns of death rates for people in this age group following other adult vaccinations. 

More Than Half Of v-safe Participants Reported Local & Systemic Reactions Following Vaccination

There were nearly eight million v-safe participants. More than half of these participants reported local and systemic reactions following vaccination, according to the study. Local reaction is one which occurs at the point of stimulation or injection of foreign substances. Meanwhile, a systemic reaction is one which occurs when inflammation spreads from a localised area of one organ, like the skin, to other organ systems in the body. 

As many as 4.6 million v-safe participants reported local reactions, while 3.6 million people reported systemic reactions following vaccination. 

According to the study, side effects were most frequently reported the day after vaccination. They were nearly all mild, with the most common being fatigue, headache and injection site pain. 

Several people reported the inability to work and to perform normal activities after the second dose, using the v-safe system. According to the study, less than one per cent of participants reported seeking medical care after either vaccine dose.

How Are VAERS & v-safe Systems Beneficial?

Dr Tom Shimabukuro, one of the authors of the study, said that VAERS and v-safe are important tools CDC can use when evaluating vaccine safety and to help identify any unexpected or unusual events. He explained that these data are reassuring that reactions to both mRNA vaccines are generally mild and subside after one or two days. 

Limitations To The Study

The authors noted some limitations to the study, including the fact that the VAERS system relies on spontaneous reporting and is not representative of the entire population. The authors said this also means that while the VAERS system can monitor for potential safety signals, it cannot define a causal relationship between vaccination and adverse events. 

According to the authors, this limitation lies with the surveillance system and not the study design. Since smartphone access is needed to participate in v-safe, the populations without access to these devices are excluded. 

The authors concluded that neither VAERS nor v-safe can definitively measure the safety differences between the Pfizer-BioNTech and Moderna mRNA vaccines.