Incidence rate for Novavax's adverse reactions higher than other COVID vaccines: HSA data

As at 31 May, four cases of adverse reactions were reported out of the 2,792 doses of Nuvaxovid administered here, at a 0.14% incidence rate.
As at 31 May, four cases of adverse reactions were reported out of the 2,792 doses of Nuvaxovid administered here, at a 0.14% incidence rate. (Reuter file photo)

SINGAPORE — The incidence rate of suspected cases of adverse reactions from Novavax COVID-19 vaccine doses given in Singapore is higher than those of the other three vaccines under the national vaccination programme, according to a Health Sciences Authority (HSA) report.

As at 31 May, four cases of adverse reactions were reported out of the 2,792 doses of Nuvaxovid administered here, at a 0.14 per cent incidence rate, the report published on Monday (27 June) shows.

All four were not serious and had reported experiencing rash, chest pain, dizziness, and vasculitis (blood vessel inflammation). "These are largely consistent with what was reported in the clinical studies and are known adverse effects associated with vaccines," HSA said.

An adverse event is classified as serious when it results in hospitalisation, a significant reduction in functioning level, a life-threatening illness, or death.

Apart from Novavax's protein-based Nuvaxovid, the other vaccines under the national vaccination programme are Sinovac's inactivated CoronaVac, and one each of the mRNA vaccines developed by Pfizer-BioNTech and Moderna.

Of the 11,168,800 Pfizer doses administered, 14,236 cases reported adverse reactions, at a 0.13 per cent incidence rate, 841 of which were serious. In comparison, of the 3,261,656 Moderna doses, 3,077 cases reported adverse reactions, at a 0.09 per cent incidence rate, 191 of which were serious.

There was no comparative data for the CoronaVac vaccine in the latest HSA report, its 12th on the roll-out of COVID-19 vaccines in Singapore.

The incidence rate of adverse events with the CoronaVac vaccine was about 0.08 per cent, or 312, of 392,122 doses administered, according to a previous HSA report in March. Of these events, 24 were serious.

No reports of myocarditis

While there have been no local reports of myocarditis – or inflammation of heart muscles – arising from Nuvaxovid doses, a small number of such cases have been observed from ongoing global clinical trials, said HSA.

As such, HSA will be monitoring the incidence rate of pericarditis – or inflammation of the outer lining of the heart – and myocarditis.

"HSA’s assessment is that although the potential risk of myocarditis with Nuvaxovid COVID-19 vaccine cannot be excluded, the benefits of the vaccine continue to outweigh the risks in the Singapore context," it said.

COVID-19 infection is also known to be associated with myocarditis, with 40 extra myocarditis events per million persons observed among those infected with the virus based on published data, according to HSA.

As a precaution, those who have been vaccinated with Nuvaxovid should avoid strenuous physical activity or exercise for two weeks after the dose to mitigate the risk of myocarditis such as running, weightlifting, and competitive sports.

The incidence rates of adverse events such as anaphylaxis, myocarditis, pericarditis, and cerebral venous thrombosis – blood clotting in the brain – with the mRNA vaccines have stabilised, HSA said.

But 21 cases of appendicitis – inflammation of the appendix – have been reported among the over 11 million Pfizer doses administered here, HSA added. All of the cases with appendicitis were discharged after hospitalisation.

A small rise in incidents of appendicitis – two additional cases per 100,000 administered doses – were observed occurring within 21 days after the primary vaccination series of the Pfizer vaccine, mainly in those aged 12 to 17.

No increased incidence of appendicitis has been observed with the booster dose of the vaccine, according to HSA.

The background incidence of appendicitis is estimated to be about 100 per 100,000 people per year. Rare cases of appendicitis have been reported following vaccination with COVID-19 vaccines globally.

As of Sunday, 92 per cent of Singapore's total population have completed their full COVID-19 vaccine regimen, while 78 per cent have received their booster shots.

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