Adverse effects of mRNA Covid-19 booster shots similar to those of first two doses: HSA

Overall, more than 9.9 million doses of mRNA vaccines were given as at Oct 31, 2021.
Overall, more than 9.9 million doses of mRNA vaccines were given as at Oct 31, 2021.ST PHOTO: KEVIN LIM

SINGAPORE - The adverse effects associated with mRNA Covid-19 booster shots are similar to those of the first two doses of such vaccines, and there is no increase in the frequency of such effects, the Health Sciences Authority (HSA) said in its Nov 16 report on the safety of Covid-19 vaccines.

HSA said there were 200 adverse events reported after 854,268 people received the mRNA booster doses as at end-October. This amounted to 0.02 per cent of the doses administered.

Singapore rolled out its booster vaccination programme on Sept 15, with the use of the Pfizer-BioNTech/Comirnaty or Moderna/Spikevax vaccine as a booster dose.

The commonly reported adverse events include rash, angioedema - or the swelling of the eyelids, face and lips - chest discomfort, palpitation, shortness of breath, fever, generalised weakness and dizziness, HSA said.

As for the rare cases of heart inflammatory conditions in young people after vaccination, HSA said there was a higher incidence of myocarditis (inflammation of the heart muscle) reported with the use of Moderna compared with the Pfizer vaccine here.

For every 100,000 doses given to those aged 18 and above, the myocarditis incidence rate for Moderna vaccine was 1.29, while the rate for Pfizer vaccine was lower at 0.62. The incidences were reported after the first or the second dose.

As the number of reports received locally is small given Singapore's small population, the HSA said it could not confirm that there is an increased risk associated with the Moderna vaccine compared with the Pfizer vaccine.

It noted that some countries such as Canada, Sweden, Norway and Finland have reported an increased risk associated with the Moderna vaccine, but "this observation is not consistently reported globally".

Pericarditis, or inflammation of the outer lining of the heart, has also been associated with mRNA Covid-19 vaccines.

The typical symptoms of the two conditions are chest pain, shortness of breath and fast heartbeat. HSA said that in most cases, the inflammation is mild, and most people who develop them respond well to treatment and recover. The risk is observed to be highest in males aged 30 years and below.

Overall, after more than 9.9 million doses of mRNA vaccines were given as at Oct 31, the HSA received 13,334 reports of suspected adverse events. Among them were 634 reports of serious events, including anaphylaxis and chest pain, and 86 reports of myocarditis and pericarditis.

HSA said that 206,722 doses of the Sinovac inactivated vaccine had been administered as at end-October and there were 171 reports of adverse events. This worked out to be 0.08 per cent of the doses administered. The commonly reported effects were rash, angioedema, shortness of breath, chest discomfort and dizziness.

Fourteen of the reports described Bell's Palsy, blood clots, numbness, muscle spasm, vertigo with tinnitus (ringing of the ears) and serious allergic reactions including anaphylaxis, HSA said. Bells' Palsy is facial muscle weakness caused by inflammation of the facial nerve.

Singapore included the three-dose Sinovac vaccine in the national vaccination programme at the end of October. The Sinovac vaccines arrived here on Feb 23, and were made available around mid-June at private healthcare providers under the Special Access Route to enhance overall vaccination coverage.

Sinopharm, rolled out on Aug 30, is the other inactivated vaccine that is available here, though it is not under the national vaccination programme.

As of Oct 31, 48,697 doses of Sinopharm had been given and 17 suspected adverse events were reported. This amounted to 0.03 per cent of the doses administered. The non-serious effects included rash, angioedema, shortness of breath, chest discomfort and tinnitus while there was one serious adverse event of low platelet count.