Side effects similar after third Covid-19 vaccine dose


Side effects from mRNA vaccine booster doses appear to be similar to those the recipients experience after their second dose. — AFP

Most side effects after a third dose of a Covid-19 vaccine are mild or moderate, and occur about as often as after shot two.

These findings by an American study on Sept 28 (2021) were expected, but nonetheless reassuring.

The report by the US Centers for Disease Control and Prevention (CDC) came from more than 22,000 people who signed up to a vaccine safety smartphone app and who had received a booster shot between Aug 12 and Sept 19 (2021).

During this time, third doses were authorised for people who are immunocompromised, but not the wider population.

“The frequency and type of side effects were similar to those seen after the second vaccine doses, and were mostly mild or moderate, and short-lived,” US CDC director Rochelle Walensky said at a press briefing.

Frequently reported side effects included injection site pain (71% of study participants), fatigue (56%) and headache (43%).

Some 28% reported being unable to perform normal daily activities, usually the next day.

Medical care was sought by around 2% of participants, and 0.1% (13 people) were hospitalised.

A subset of almost 21,700 who received the same mRNA (messenger ribonucleic acid) vaccine (Moderna or Pfizer/BioNTech) for all three of their doses was further analysed.

Among those who received the Moderna vaccine, localised reactions, such as arm pain, were reported to be slightly more common after the third dose, compared to the second.

Systemic reactions – meaning those that occurred outside the injection site – were slightly less frequent after the third dose, compared to the second.

The same pattern occurred for the Pfizer/BioNTech vaccine.

For both vaccines, the first shots resulted in significantly less frequent side effects, especially systemic, compared to shots two and three.

On Sept 22 (2021), US health agencies expanded authorisation of Pfizer/BioNTech booster doses to those aged over 65, those aged 18 to 64 with an underlying medical condition such as diabetes or obesity, and those who are especially exposed to the virus because of their work or where they live.

The US CDC cautioned that there were certain limitations to its report.

These include the fact that signing up to the smartphone app called “v-safe” was voluntary and the participants skewed more heavily white than the US population.

During the study period, some non-immunocompromised individuals may have also received a booster outside of recommendations because they were worried about waning immunity.

Therefore, the findings cannot be reliably linked to immunocompromised people only. – AFP Relaxnews

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