Despite some side effects, vaccines are safe and effective to use, South African Medical Research Council (SAMRC) CEO Professor Glenda Gray has said.

In a briefing by the health department on Friday, Gray said the only way to control the pandemic is through global immunisation.

She said both vaccines currently used in South Africa – Johnson & Johnson (J&J) and Pfizer – are safe to use and effective against the Delta variant of the coronavirus.

Gray added that some side effects of the vaccines include swelling, redness and pain at the injection site, as well as fever, headaches, tiredness, muscle pain, chills and nausea.

She said some rare side effects, which had been recorded internationally, included thrombocytopenia syndrome (TTS), anaphylaxis, myocarditis/pericarditis and Guillain-Barré Syndrome.

TTS linked to the J&J vaccinations have been recorded at three cases for every million vaccinations administered to adults. Also linked to the J&J vaccine has been Guillain-Barré Syndrome, which showed 7.8 cases for every million doses administered.

Myocarditis, linked to the Pfizer vaccine, presented only 3.5 cases for every million doses administered to adults.

In comparison, one-million J&J vaccine doses could prevent more than 3 400 deaths, while one-million Pfizer doses could prevent more than 3-600 deaths, Gray said.

The benefits of vaccines far outweighed the risks, Gray said.

"Serious side effects that could cause a long-term health problem are extremely unlikely following any vaccination, including Covid-19 vaccination," Gray said.

Adverse side effects are most likely to happen within six weeks of receiving the vaccine.

"Millions of people have received Covid-19 vaccines, and no long-term side effects have been detected," she added.

Gray also said 28 deaths following vaccination in South Africa were under investigation to determine the cause of death.

She added that those who experience adverse reactions due to the vaccine should contact their doctor or the health department so that these could be studied to establish the cause.